Topics

475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?


stan_katz
 

I know I've let this thread go cold, but I assure members it wasn't out of neglect. For one thing, I was advised to read the manual, and I have been doing so. In the meantime, I had been monitoring the trigger diodes by clipping scope probes on their anodes. I intended on recording waveforms with my digital camera. Alas, I found the camera was fried. Nevertheless, I decided to do some more examination of the Trigger A circuits. I took hold of one of the probes attached to a tunnel diode, intending to disengage it. The instrument was powered on. The probe came off the board, WITH THE TUNNEL DIODE STILL ATTACHED to the probe! The diode had no sign of being soldered in. I turned off the instrument, and pulled on the other tunnel diode, and it came out. No solder. Now it sunk in. Those phosphor/bronze stakes weren't hiding solder pads underneath, they were all sockets! I must have missed that in some FAQ or manual addendum. The only semiconductors soldered in my 475 are small signal diodes. Who knows if my probes were intermittently yanking out the anode ends of the TDs. I certainly wasn't going to waste members' time by trying to diagnose TD damage. I bit my lip, and purchased two NOS tunnel diodes for $OUCH.00. As least this message would start with good tunnel diodes.

Following David's advise to do a modified 5-40 trigger A calibration from just Channel 1 input lead me nowhere. The scope wouldn't trigger on the 12mv p-p 350khz sine wave I was using to obtain a .32 division height on the CRT. Adjusting R565 had no effect. Lowering the attenuator and filling the screen with the signal also had no effect. I then returned the trigger level to full + ( clockwise ), attenuator down to 50mv, and with the waveform filling the screen, I got trigger lock. I did note, that during the modified 5-40 calibration attempt, there was no sign of the trigger signal with TRIG VIEW depressed. However, with the intentional misadjustments reported above, I could just see some light at the top of the screen in TRIG VIEW. Although I was advised not to start messing with anything but R565, I adjusted R534 in the "misadjusted" state using TRIG VIEW. The waveform came into view, and I could center it. With this set of adjustments, I could now trigger on the 12mv waveform with the attenuator turned up to .1v so that I could meet the .32 divisions performance called out in 5-40. I thought I was on to something regarding the trigger centering. I esr'ed all the electrolytics in the triggering section. All checked out. A separate check with a VOM didn't show shorted electrolytics. I thought there may be a fault with U520, and given both it, and U720 were both socketed, I swapped them. No change. I haven't been able to find any shorted bypass caps..yet. I replaced Q532, and two resistors that were more than 50% out of spec. No go. One thing that bothers me is that, on the schematic, the emitter of Q532, is pulled up through R535 to +8.2v. I only measure +5.0v. I can't find any errata that verifies my measurement. The 8.2v source is functioning as it is available everywhere else noted on partial A8 schematic with trigger circuit. Trigger level at pin 14 of U520 varies from 1.7v (full + level) to 200mv (full - level). Is this OK? TP526 has a copy of the 12mv waveform as expected. I'm fixated on the centering circuit, but can go no further. With HORIZ DISPLAY on A LOCK, there shouldn't be any interaction with TRIG B? Right? I suppose trimmer 534 could be bad, but checking that out requires flipping A8. Yeesh! I haven't messed with R673 yet, as my troubleshooting has been with AC coupling only. Should I go there?

Stan

--- In TekScopes@..., "stan_katz" <stan_katz@...> wrote:

Dave,

I got it now.

Thanks,

Stan



--- In TekScopes@..., David wrote:

That is why I said in an earlier post, "Do not let the equipment
requirements or setup dissuade you as you can certainly complete it if
you can generate sine or triangle waveforms from 0.35 to 2 divisions."

All you need to do is connect the signal or function generator to the
channel 1 or channel 2 input with a short BNC patch cable and produce
a 50 kHz to 350 kHz sine or triangle wave with a CRT deflection of
0.35 divisions to 2 or 3 divisions. The vertical volts/div settings
are relatively unimportant because the internal trigger circuits see
exactly what is displayed on the CRT.

I would not worry about the external trigger calibration until you
verify that the internal trigger is working correctly and even then,
all that is really needed is a BNC T-connector to use as a splitter
and maybe an attenuator.

On Thu, 31 Jan 2013 00:23:28 -0000, "stan_katz"
wrote:

I can study the manual. What I can't do is figure out what cabling and interface devices I need. What's a 50ohm 5ns GR cable (GR stands for General Radio?). What's a 50ohm signal pickoff unit, GR to BNC adapter, X10 attenuator (a standalone cabled inline attenuator??). Sorry I'm so dense here, but I need help to cobble together whatever is alluded to here. All I have is a signal generator, and a bunch of 50ohm cables. I have a feeling if I were a ham radio guy, the above stuff would be obvious. Maybe someone can post Ebay links to whatever it is I should order. In the meantime, I'll continue to do my homework reading the manual.

Stan

--- In TekScopes@..., "Max Mazza" wrote:

If you finally have a good and decent copy of the manual, you can finally do the work in a right manner.
The page relevant to you should be 5-40 and followings.
However I recommend to pause and read carefully the manual first, then proceed calmly.

The best sensitivity when adjusting R565 should be checked with the trigger level position to 0, not full clockwise, anyway. Fully clockwise implies that you raises the trigger level very above 0 V. The level spans from -8V to +5.2V. In normal operation the trigger level should be near 0. You can vary trigger level only if you knows what you are doing.... for instance, when there are noisy signals, they can generate spurious or false triggering; in that case it's obvious to raise the trigger level just above 0 level, up to the point where a stable waveform can be displayed.

Moreover, if you have touched R534 (A trig centering), it's easy that you have altered the 0 level for the trigger level knob....

Conclusion: study carefully the manual first, then resume the process on your 475. The calibration procedures are somewhat complicated in some cases, and they require a lot of patience and calm.
No problem if you want to contact me directly, but I think that it's better that you post your questions here, since "many brains are better tha one :-)

Don't rely strong on my suggestion to read +80mV, it's an extreme simplification to help you to make your scope functioning with the instrumentation in your possess. Read the manual first, then ask with no problem!

Max

--- In TekScopes@..., "stan_katz" wrote:

I've finally downloaded REAL Tek 457 manual. MUCH better manual. Thanks Dave. Max, I think I've fiddled with R565 to get the best sensitivity possible. That is + trigger slope cranked fully clockwise, and max attenuation possible of .5v/div. I'll keep on trying to do better. I might try to upload sketches of the waveforms I now have to Archive 2. It would be easier to just email. Can I get permission to email direct?..Max?..Dave? As for detecting +80mv on my little D51, that's a stretch. Do my best tho.

Stan

Stan

Stan



------------------------------------

Yahoo! Groups Links



 

If those low profile socket elements are the ones I am thinking of,
they are called Miniserts. I have had at least two incidents now
where a Minisert was open and reseating the lead at least temporarily
fixed the problem.

There is a datasheet for them in the files area:

http://f1.grp.yahoofs.com/v1/5EskUWIwdScdLDCLRHNKBOlgfv-EbF0Km21vDCqeT_vx9Vh_SFUazvNofOxE469fMyGLxa74BOyQSCw8uTjrptaMWNJNuWVtKXJ4M4LBses/Minisert.pdf

Q532 (and Q526) are operating as emitter followers. The emitter
voltages for each are low impedance and should be about 0.6 volts
higher than their base voltages at all times. They are just used as
simple voltage buffers.

Trigger B is completely independent from trigger A and is only used if
a sweep mode other than A internal is selected.

From your description I suspect everything is working but that the A
trigger circuit needs to be calibrated:

R534 is used to center the trigger point vertically on the CRT when
R530 is in the middle of its rotation.

R673 adjusts the trigger view vertical positioning on the CRT.

R547 adjusts the trigger level so that it does not change when the
slope is changed.

R565 adjusts the tunnel diode threshold for maximum sensitivity.

On Wed, 20 Feb 2013 02:17:18 -0000, "stan_katz" <stan_katz@...>
wrote:

I know I've let this thread go cold, but I assure members it wasn't out of neglect. For one thing, I was advised to read the manual, and I have been doing so. In the meantime, I had been monitoring the trigger diodes by clipping scope probes on their anodes. I intended on recording waveforms with my digital camera. Alas, I found the camera was fried. Nevertheless, I decided to do some more examination of the Trigger A circuits. I took hold of one of the probes attached to a tunnel diode, intending to disengage it. The instrument was powered on. The probe came off the board, WITH THE TUNNEL DIODE STILL ATTACHED to the probe! The diode had no sign of being soldered in. I turned off the instrument, and pulled on the other tunnel diode, and it came out. No solder. Now it sunk in. Those phosphor/bronze stakes weren't hiding solder pads underneath, they were all sockets! I must have missed that in some FAQ or manual addendum. The only semiconductors soldered in my 475 are small signal
diodes. Who knows if my probes were intermittently yanking out the anode ends of the TDs. I certainly wasn't going to waste members' time by trying to diagnose TD damage. I bit my lip, and purchased two NOS tunnel diodes for $OUCH.00. As least this message would start with good tunnel diodes.

Following David's advise to do a modified 5-40 trigger A calibration from just Channel 1 input lead me nowhere. The scope wouldn't trigger on the 12mv p-p 350khz sine wave I was using to obtain a .32 division height on the CRT. Adjusting R565 had no effect. Lowering the attenuator and filling the screen with the signal also had no effect. I then returned the trigger level to full + ( clockwise ), attenuator down to 50mv, and with the waveform filling the screen, I got trigger lock. I did note, that during the modified 5-40 calibration attempt, there was no sign of the trigger signal with TRIG VIEW depressed. However, with the intentional misadjustments reported above, I could just see some light at the top of the screen in TRIG VIEW. Although I was advised not to start messing with anything but R565, I adjusted R534 in the "misadjusted" state using TRIG VIEW. The waveform came into view, and I could center it. With this set of adjustments, I could now trigger on the 12mv waveform
with the attenuator turned up to .1v so that I could meet the .32 divisions performance called out in 5-40. I thought I was on to something regarding the trigger centering. I esr'ed all the electrolytics in the triggering section. All checked out. A separate check with a VOM didn't show shorted electrolytics. I thought there may be a fault with U520, and given both it, and U720 were both socketed, I swapped them. No change. I haven't been able to find any shorted bypass caps..yet. I replaced Q532, and two resistors that were more than 50% out of spec. No go. One thing that bothers me is that, on the schematic, the emitter of Q532, is pulled up through R535 to +8.2v. I only measure +5.0v. I can't find any errata that verifies my measurement. The 8.2v source is functioning as it is available everywhere else noted on partial A8 schematic with trigger circuit. Trigger level at pin 14 of U520 varies from 1.7v (full + level) to 200mv (full - level). Is this OK? TP526 has a copy of the 12mv
waveform as expected. I'm fixated on the centering circuit, but can go no further. With HORIZ DISPLAY on A LOCK, there shouldn't be any interaction with TRIG B? Right? I suppose trimmer 534 could be bad, but checking that out requires flipping A8. Yeesh! I haven't messed with R673 yet, as my troubleshooting has been with AC coupling only. Should I go there?


raymonddompfrank <r.domp.frank@...>
 

I haven't followed this thread but noticed that you purchased new TD's and as David says, your adjustments seem to be (quite far) off.
Did you purchase the right TD's? They're not all the same!
Peak currents vary from 1mA to more than 10mA. They need appropriate biase adjustments!

Raymond

--- In TekScopes@..., David <davidwhess@...> wrote:

If those low profile socket elements are the ones I am thinking of,
they are called Miniserts. I have had at least two incidents now
where a Minisert was open and reseating the lead at least temporarily
fixed the problem.

There is a datasheet for them in the files area:

http://f1.grp.yahoofs.com/v1/5EskUWIwdScdLDCLRHNKBOlgfv-EbF0Km21vDCqeT_vx9Vh_SFUazvNofOxE469fMyGLxa74BOyQSCw8uTjrptaMWNJNuWVtKXJ4M4LBses/Minisert.pdf

Q532 (and Q526) are operating as emitter followers. The emitter
voltages for each are low impedance and should be about 0.6 volts
higher than their base voltages at all times. They are just used as
simple voltage buffers.

Trigger B is completely independent from trigger A and is only used if
a sweep mode other than A internal is selected.

From your description I suspect everything is working but that the A
trigger circuit needs to be calibrated:

R534 is used to center the trigger point vertically on the CRT when
R530 is in the middle of its rotation.

R673 adjusts the trigger view vertical positioning on the CRT.

R547 adjusts the trigger level so that it does not change when the
slope is changed.

R565 adjusts the tunnel diode threshold for maximum sensitivity.

On Wed, 20 Feb 2013 02:17:18 -0000, "stan_katz" <stan_katz@...>
wrote:

I know I've let this thread go cold, but I assure members it wasn't out of neglect. For one thing, I was advised to read the manual, and I have been doing so. In the meantime, I had been monitoring the trigger diodes by clipping scope probes on their anodes. I intended on recording waveforms with my digital camera. Alas, I found the camera was fried. Nevertheless, I decided to do some more examination of the Trigger A circuits. I took hold of one of the probes attached to a tunnel diode, intending to disengage it. The instrument was powered on. The probe came off the board, WITH THE TUNNEL DIODE STILL ATTACHED to the probe! The diode had no sign of being soldered in. I turned off the instrument, and pulled on the other tunnel diode, and it came out. No solder. Now it sunk in. Those phosphor/bronze stakes weren't hiding solder pads underneath, they were all sockets! I must have missed that in some FAQ or manual addendum. The only semiconductors soldered in my 475 are small signal
diodes. Who knows if my probes were intermittently yanking out the anode ends of the TDs. I certainly wasn't going to waste members' time by trying to diagnose TD damage. I bit my lip, and purchased two NOS tunnel diodes for $OUCH.00. As least this message would start with good tunnel diodes.

Following David's advise to do a modified 5-40 trigger A calibration from just Channel 1 input lead me nowhere. The scope wouldn't trigger on the 12mv p-p 350khz sine wave I was using to obtain a .32 division height on the CRT. Adjusting R565 had no effect. Lowering the attenuator and filling the screen with the signal also had no effect. I then returned the trigger level to full + ( clockwise ), attenuator down to 50mv, and with the waveform filling the screen, I got trigger lock. I did note, that during the modified 5-40 calibration attempt, there was no sign of the trigger signal with TRIG VIEW depressed. However, with the intentional misadjustments reported above, I could just see some light at the top of the screen in TRIG VIEW. Although I was advised not to start messing with anything but R565, I adjusted R534 in the "misadjusted" state using TRIG VIEW. The waveform came into view, and I could center it. With this set of adjustments, I could now trigger on the 12mv waveform
with the attenuator turned up to .1v so that I could meet the .32 divisions performance called out in 5-40. I thought I was on to something regarding the trigger centering. I esr'ed all the electrolytics in the triggering section. All checked out. A separate check with a VOM didn't show shorted electrolytics. I thought there may be a fault with U520, and given both it, and U720 were both socketed, I swapped them. No change. I haven't been able to find any shorted bypass caps..yet. I replaced Q532, and two resistors that were more than 50% out of spec. No go. One thing that bothers me is that, on the schematic, the emitter of Q532, is pulled up through R535 to +8.2v. I only measure +5.0v. I can't find any errata that verifies my measurement. The 8.2v source is functioning as it is available everywhere else noted on partial A8 schematic with trigger circuit. Trigger level at pin 14 of U520 varies from 1.7v (full + level) to 200mv (full - level). Is this OK? TP526 has a copy of the 12mv
waveform as expected. I'm fixated on the centering circuit, but can go no further. With HORIZ DISPLAY on A LOCK, there shouldn't be any interaction with TRIG B? Right? I suppose trimmer 534 could be bad, but checking that out requires flipping A8. Yeesh! I haven't messed with R673 yet, as my troubleshooting has been with AC coupling only. Should I go there?


stan_katz
 

I purchased original NOS Tektronix p/n tunnel diodes listed in the 475 manual.

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@...> wrote:

I haven't followed this thread but noticed that you purchased new TD's and as David says, your adjustments seem to be (quite far) off.
Did you purchase the right TD's? They're not all the same!
Peak currents vary from 1mA to more than 10mA. They need appropriate biase adjustments!

Raymond

--- In TekScopes@..., David <davidwhess@> wrote:

If those low profile socket elements are the ones I am thinking of,
they are called Miniserts. I have had at least two incidents now
where a Minisert was open and reseating the lead at least temporarily
fixed the problem.

There is a datasheet for them in the files area:

http://f1.grp.yahoofs.com/v1/5EskUWIwdScdLDCLRHNKBOlgfv-EbF0Km21vDCqeT_vx9Vh_SFUazvNofOxE469fMyGLxa74BOyQSCw8uTjrptaMWNJNuWVtKXJ4M4LBses/Minisert.pdf

Q532 (and Q526) are operating as emitter followers. The emitter
voltages for each are low impedance and should be about 0.6 volts
higher than their base voltages at all times. They are just used as
simple voltage buffers.

Trigger B is completely independent from trigger A and is only used if
a sweep mode other than A internal is selected.

From your description I suspect everything is working but that the A
trigger circuit needs to be calibrated:

R534 is used to center the trigger point vertically on the CRT when
R530 is in the middle of its rotation.

R673 adjusts the trigger view vertical positioning on the CRT.

R547 adjusts the trigger level so that it does not change when the
slope is changed.

R565 adjusts the tunnel diode threshold for maximum sensitivity.

On Wed, 20 Feb 2013 02:17:18 -0000, "stan_katz" <stan_katz@>
wrote:

I know I've let this thread go cold, but I assure members it wasn't out of neglect. For one thing, I was advised to read the manual, and I have been doing so. In the meantime, I had been monitoring the trigger diodes by clipping scope probes on their anodes. I intended on recording waveforms with my digital camera. Alas, I found the camera was fried. Nevertheless, I decided to do some more examination of the Trigger A circuits. I took hold of one of the probes attached to a tunnel diode, intending to disengage it. The instrument was powered on. The probe came off the board, WITH THE TUNNEL DIODE STILL ATTACHED to the probe! The diode had no sign of being soldered in. I turned off the instrument, and pulled on the other tunnel diode, and it came out. No solder. Now it sunk in. Those phosphor/bronze stakes weren't hiding solder pads underneath, they were all sockets! I must have missed that in some FAQ or manual addendum. The only semiconductors soldered in my 475 are small signal
diodes. Who knows if my probes were intermittently yanking out the anode ends of the TDs. I certainly wasn't going to waste members' time by trying to diagnose TD damage. I bit my lip, and purchased two NOS tunnel diodes for $OUCH.00. As least this message would start with good tunnel diodes.

Following David's advise to do a modified 5-40 trigger A calibration from just Channel 1 input lead me nowhere. The scope wouldn't trigger on the 12mv p-p 350khz sine wave I was using to obtain a .32 division height on the CRT. Adjusting R565 had no effect. Lowering the attenuator and filling the screen with the signal also had no effect. I then returned the trigger level to full + ( clockwise ), attenuator down to 50mv, and with the waveform filling the screen, I got trigger lock. I did note, that during the modified 5-40 calibration attempt, there was no sign of the trigger signal with TRIG VIEW depressed. However, with the intentional misadjustments reported above, I could just see some light at the top of the screen in TRIG VIEW. Although I was advised not to start messing with anything but R565, I adjusted R534 in the "misadjusted" state using TRIG VIEW. The waveform came into view, and I could center it. With this set of adjustments, I could now trigger on the 12mv waveform
with the attenuator turned up to .1v so that I could meet the .32 divisions performance called out in 5-40. I thought I was on to something regarding the trigger centering. I esr'ed all the electrolytics in the triggering section. All checked out. A separate check with a VOM didn't show shorted electrolytics. I thought there may be a fault with U520, and given both it, and U720 were both socketed, I swapped them. No change. I haven't been able to find any shorted bypass caps..yet. I replaced Q532, and two resistors that were more than 50% out of spec. No go. One thing that bothers me is that, on the schematic, the emitter of Q532, is pulled up through R535 to +8.2v. I only measure +5.0v. I can't find any errata that verifies my measurement. The 8.2v source is functioning as it is available everywhere else noted on partial A8 schematic with trigger circuit. Trigger level at pin 14 of U520 varies from 1.7v (full + level) to 200mv (full - level). Is this OK? TP526 has a copy of the 12mv
waveform as expected. I'm fixated on the centering circuit, but can go no further. With HORIZ DISPLAY on A LOCK, there shouldn't be any interaction with TRIG B? Right? I suppose trimmer 534 could be bad, but checking that out requires flipping A8. Yeesh! I haven't messed with R673 yet, as my troubleshooting has been with AC coupling only. Should I go there?


raymonddompfrank <r.domp.frank@...>
 

OK, glad to hear that!

Raymond

--- In TekScopes@..., "stan_katz" <stan_katz@...> wrote:

I purchased original NOS Tektronix p/n tunnel diodes listed in the 475 manual.

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

I haven't followed this thread but noticed that you purchased new TD's and as David says, your adjustments seem to be (quite far) off.
Did you purchase the right TD's? They're not all the same!
Peak currents vary from 1mA to more than 10mA. They need appropriate biase adjustments!

Raymond

--- In TekScopes@..., David <davidwhess@> wrote:

If those low profile socket elements are the ones I am thinking of,
they are called Miniserts. I have had at least two incidents now
where a Minisert was open and reseating the lead at least temporarily
fixed the problem.

There is a datasheet for them in the files area:

http://f1.grp.yahoofs.com/v1/5EskUWIwdScdLDCLRHNKBOlgfv-EbF0Km21vDCqeT_vx9Vh_SFUazvNofOxE469fMyGLxa74BOyQSCw8uTjrptaMWNJNuWVtKXJ4M4LBses/Minisert.pdf

Q532 (and Q526) are operating as emitter followers. The emitter
voltages for each are low impedance and should be about 0.6 volts
higher than their base voltages at all times. They are just used as
simple voltage buffers.

Trigger B is completely independent from trigger A and is only used if
a sweep mode other than A internal is selected.

From your description I suspect everything is working but that the A
trigger circuit needs to be calibrated:

R534 is used to center the trigger point vertically on the CRT when
R530 is in the middle of its rotation.

R673 adjusts the trigger view vertical positioning on the CRT.

R547 adjusts the trigger level so that it does not change when the
slope is changed.

R565 adjusts the tunnel diode threshold for maximum sensitivity.

On Wed, 20 Feb 2013 02:17:18 -0000, "stan_katz" <stan_katz@>
wrote:

I know I've let this thread go cold, but I assure members it wasn't out of neglect. For one thing, I was advised to read the manual, and I have been doing so. In the meantime, I had been monitoring the trigger diodes by clipping scope probes on their anodes. I intended on recording waveforms with my digital camera. Alas, I found the camera was fried. Nevertheless, I decided to do some more examination of the Trigger A circuits. I took hold of one of the probes attached to a tunnel diode, intending to disengage it. The instrument was powered on. The probe came off the board, WITH THE TUNNEL DIODE STILL ATTACHED to the probe! The diode had no sign of being soldered in. I turned off the instrument, and pulled on the other tunnel diode, and it came out. No solder. Now it sunk in. Those phosphor/bronze stakes weren't hiding solder pads underneath, they were all sockets! I must have missed that in some FAQ or manual addendum. The only semiconductors soldered in my 475 are small signal
diodes. Who knows if my probes were intermittently yanking out the anode ends of the TDs. I certainly wasn't going to waste members' time by trying to diagnose TD damage. I bit my lip, and purchased two NOS tunnel diodes for $OUCH.00. As least this message would start with good tunnel diodes.

Following David's advise to do a modified 5-40 trigger A calibration from just Channel 1 input lead me nowhere. The scope wouldn't trigger on the 12mv p-p 350khz sine wave I was using to obtain a .32 division height on the CRT. Adjusting R565 had no effect. Lowering the attenuator and filling the screen with the signal also had no effect. I then returned the trigger level to full + ( clockwise ), attenuator down to 50mv, and with the waveform filling the screen, I got trigger lock. I did note, that during the modified 5-40 calibration attempt, there was no sign of the trigger signal with TRIG VIEW depressed. However, with the intentional misadjustments reported above, I could just see some light at the top of the screen in TRIG VIEW. Although I was advised not to start messing with anything but R565, I adjusted R534 in the "misadjusted" state using TRIG VIEW. The waveform came into view, and I could center it. With this set of adjustments, I could now trigger on the 12mv waveform
with the attenuator turned up to .1v so that I could meet the .32 divisions performance called out in 5-40. I thought I was on to something regarding the trigger centering. I esr'ed all the electrolytics in the triggering section. All checked out. A separate check with a VOM didn't show shorted electrolytics. I thought there may be a fault with U520, and given both it, and U720 were both socketed, I swapped them. No change. I haven't been able to find any shorted bypass caps..yet. I replaced Q532, and two resistors that were more than 50% out of spec. No go. One thing that bothers me is that, on the schematic, the emitter of Q532, is pulled up through R535 to +8.2v. I only measure +5.0v. I can't find any errata that verifies my measurement. The 8.2v source is functioning as it is available everywhere else noted on partial A8 schematic with trigger circuit. Trigger level at pin 14 of U520 varies from 1.7v (full + level) to 200mv (full - level). Is this OK? TP526 has a copy of the 12mv
waveform as expected. I'm fixated on the centering circuit, but can go no further. With HORIZ DISPLAY on A LOCK, there shouldn't be any interaction with TRIG B? Right? I suppose trimmer 534 could be bad, but checking that out requires flipping A8. Yeesh! I haven't messed with R673 yet, as my troubleshooting has been with AC coupling only. Should I go there?


stan_katz
 

SOLVED...while pin 3 of U520 had a good copy of the waveform being triggered on, the DC voltage on pin 3 was 1.6v. I found the U520 pin voltages posted by Tom Miller and noted that proper voltage for pin 3 should be .7v. In addition, the base of Q526 had almost 1 volt on it. Not right! I don't have a curve tracer but a simple DMM probing of the diff amp JFETS proved Q522 was blown. Ordered another matched pair and my 475 is back on the air. Now...with all my troubleshooting cal. tweaks behind me, this scope can really use a good calibration. Whew!

Thanks - Tom, David, Max, Albert, et.al
Stan

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@...> wrote:

OK, glad to hear that!

Raymond

--- In TekScopes@..., "stan_katz" <stan_katz@> wrote:

I purchased original NOS Tektronix p/n tunnel diodes listed in the 475 manual.

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

I haven't followed this thread but noticed that you purchased new TD's and as David says, your adjustments seem to be (quite far) off.
Did you purchase the right TD's? They're not all the same!
Peak currents vary from 1mA to more than 10mA. They need appropriate biase adjustments!

Raymond

--- In TekScopes@..., David <davidwhess@> wrote:

If those low profile socket elements are the ones I am thinking of,
they are called Miniserts. I have had at least two incidents now
where a Minisert was open and reseating the lead at least temporarily
fixed the problem.

There is a datasheet for them in the files area:

http://f1.grp.yahoofs.com/v1/5EskUWIwdScdLDCLRHNKBOlgfv-EbF0Km21vDCqeT_vx9Vh_SFUazvNofOxE469fMyGLxa74BOyQSCw8uTjrptaMWNJNuWVtKXJ4M4LBses/Minisert.pdf

Q532 (and Q526) are operating as emitter followers. The emitter
voltages for each are low impedance and should be about 0.6 volts
higher than their base voltages at all times. They are just used as
simple voltage buffers.

Trigger B is completely independent from trigger A and is only used if
a sweep mode other than A internal is selected.

From your description I suspect everything is working but that the A
trigger circuit needs to be calibrated:

R534 is used to center the trigger point vertically on the CRT when
R530 is in the middle of its rotation.

R673 adjusts the trigger view vertical positioning on the CRT.

R547 adjusts the trigger level so that it does not change when the
slope is changed.

R565 adjusts the tunnel diode threshold for maximum sensitivity.

On Wed, 20 Feb 2013 02:17:18 -0000, "stan_katz" <stan_katz@>
wrote:

I know I've let this thread go cold, but I assure members it wasn't out of neglect. For one thing, I was advised to read the manual, and I have been doing so. In the meantime, I had been monitoring the trigger diodes by clipping scope probes on their anodes. I intended on recording waveforms with my digital camera. Alas, I found the camera was fried. Nevertheless, I decided to do some more examination of the Trigger A circuits. I took hold of one of the probes attached to a tunnel diode, intending to disengage it. The instrument was powered on. The probe came off the board, WITH THE TUNNEL DIODE STILL ATTACHED to the probe! The diode had no sign of being soldered in. I turned off the instrument, and pulled on the other tunnel diode, and it came out. No solder. Now it sunk in. Those phosphor/bronze stakes weren't hiding solder pads underneath, they were all sockets! I must have missed that in some FAQ or manual addendum. The only semiconductors soldered in my 475 are small signal
diodes. Who knows if my probes were intermittently yanking out the anode ends of the TDs. I certainly wasn't going to waste members' time by trying to diagnose TD damage. I bit my lip, and purchased two NOS tunnel diodes for $OUCH.00. As least this message would start with good tunnel diodes.

Following David's advise to do a modified 5-40 trigger A calibration from just Channel 1 input lead me nowhere. The scope wouldn't trigger on the 12mv p-p 350khz sine wave I was using to obtain a .32 division height on the CRT. Adjusting R565 had no effect. Lowering the attenuator and filling the screen with the signal also had no effect. I then returned the trigger level to full + ( clockwise ), attenuator down to 50mv, and with the waveform filling the screen, I got trigger lock. I did note, that during the modified 5-40 calibration attempt, there was no sign of the trigger signal with TRIG VIEW depressed. However, with the intentional misadjustments reported above, I could just see some light at the top of the screen in TRIG VIEW. Although I was advised not to start messing with anything but R565, I adjusted R534 in the "misadjusted" state using TRIG VIEW. The waveform came into view, and I could center it. With this set of adjustments, I could now trigger on the 12mv waveform
with the attenuator turned up to .1v so that I could meet the .32 divisions performance called out in 5-40. I thought I was on to something regarding the trigger centering. I esr'ed all the electrolytics in the triggering section. All checked out. A separate check with a VOM didn't show shorted electrolytics. I thought there may be a fault with U520, and given both it, and U720 were both socketed, I swapped them. No change. I haven't been able to find any shorted bypass caps..yet. I replaced Q532, and two resistors that were more than 50% out of spec. No go. One thing that bothers me is that, on the schematic, the emitter of Q532, is pulled up through R535 to +8.2v. I only measure +5.0v. I can't find any errata that verifies my measurement. The 8.2v source is functioning as it is available everywhere else noted on partial A8 schematic with trigger circuit. Trigger level at pin 14 of U520 varies from 1.7v (full + level) to 200mv (full - level). Is this OK? TP526 has a copy of the 12mv
waveform as expected. I'm fixated on the centering circuit, but can go no further. With HORIZ DISPLAY on A LOCK, there shouldn't be any interaction with TRIG B? Right? I suppose trimmer 534 could be bad, but checking that out requires flipping A8. Yeesh! I haven't messed with R673 yet, as my troubleshooting has been with AC coupling only. Should I go there?


 

Good job Stan. Thanks for sharing your results as I am sure someone in the future will benefit from your work.
 
Regards,
Tom
 

----- Original Message -----
From: stan_katz
Sent: Sunday, February 24, 2013 8:21 PM
Subject: [TekScopes] Re: 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?

 


SOLVED...while pin 3 of U520 had a good copy of the waveform being triggered on, the DC voltage on pin 3 was 1.6v. I found the U520 pin voltages posted by Tom Miller and noted that proper voltage for pin 3 should be .7v. In addition, the base of Q526 had almost 1 volt on it. Not right! I don't have a curve tracer but a simple DMM probing of the diff amp JFETS proved Q522 was blown. Ordered another matched pair and my 475 is back on the air. Now...with all my troubleshooting cal. tweaks behind me, this scope can really use a good calibration. Whew!

Thanks - Tom, David, Max, Albert, et.al
Stan

--- In TekScopes@..., "raymonddompfrank" wrote:
>
> OK, glad to hear that!
>
> Raymond
>
> --- In TekScopes@..., "stan_katz" wrote:
> >
> > I purchased original NOS Tektronix p/n tunnel diodes listed in the 475 manual.
> >
> > --- In TekScopes@..., "raymonddompfrank" wrote:
> > >
> > > I haven't followed this thread but noticed that you purchased new TD's and as David says, your adjustments seem to be (quite far) off.
> > > Did you purchase the right TD's? They're not all the same!
> > > Peak currents vary from 1mA to more than 10mA. They need appropriate biase adjustments!
> > >
> > > Raymond
> > >
> > > --- In TekScopes@..., David wrote:
> > > >
> > > > If those low profile socket elements are the ones I am thinking of,
> > > > they are called Miniserts. I have had at least two incidents now
> > > > where a Minisert was open and reseating the lead at least temporarily
> > > > fixed the problem.
> > > >
> > > > There is a datasheet for them in the files area:
> > > >
> > > > http://f1.grp.yahoofs.com/v1/5EskUWIwdScdLDCLRHNKBOlgfv-EbF0Km21vDCqeT_vx9Vh_SFUazvNofOxE469fMyGLxa74BOyQSCw8uTjrptaMWNJNuWVtKXJ4M4LBses/Minisert.pdf
> > > >
> > > > Q532 (and Q526) are operating as emitter followers. The emitter
> > > > voltages for each are low impedance and should be about 0.6 volts
> > > > higher than their base voltages at all times. They are just used as
> > > > simple voltage buffers.
> > > >
> > > > Trigger B is completely independent from trigger A and is only used if
> > > > a sweep mode other than A internal is selected.
> > > >
> > > > From your description I suspect everything is working but that the A
> > > > trigger circuit needs to be calibrated:
> > > >
> > > > R534 is used to center the trigger point vertically on the CRT when
> > > > R530 is in the middle of its rotation.
> > > >
> > > > R673 adjusts the trigger view vertical positioning on the CRT.
> > > >
> > > > R547 adjusts the trigger level so that it does not change when the
> > > > slope is changed.
> > > >
> > > > R565 adjusts the tunnel diode threshold for maximum sensitivity.
> > > >
> > > > On Wed, 20 Feb 2013 02:17:18 -0000, "stan_katz"
> > > > wrote:
> > > >
> > > > >I know I've let this thread go cold, but I assure members it wasn't out of neglect. For one thing, I was advised to read the manual, and I have been doing so. In the meantime, I had been monitoring the trigger diodes by clipping scope probes on their anodes. I intended on recording waveforms with my digital camera. Alas, I found the camera was fried. Nevertheless, I decided to do some more examination of the Trigger A circuits. I took hold of one of the probes attached to a tunnel diode, intending to disengage it. The instrument was powered on. The probe came off the board, WITH THE TUNNEL DIODE STILL ATTACHED to the probe! The diode had no sign of being soldered in. I turned off the instrument, and pulled on the other tunnel diode, and it came out. No solder. Now it sunk in. Those phosphor/bronze stakes weren't hiding solder pads underneath, they were all sockets! I must have missed that in some FAQ or manual addendum. The only semiconductors soldered in my 475 are small signal
> > > > >diodes. Who knows if my probes were intermittently yanking out the anode ends of the TDs. I certainly wasn't going to waste members' time by trying to diagnose TD damage. I bit my lip, and purchased two NOS tunnel diodes for $OUCH.00. As least this message would start with good tunnel diodes.
> > > > >
> > > > >Following David's advise to do a modified 5-40 trigger A calibration from just Channel 1 input lead me nowhere. The scope wouldn't trigger on the 12mv p-p 350khz sine wave I was using to obtain a .32 division height on the CRT. Adjusting R565 had no effect. Lowering the attenuator and filling the screen with the signal also had no effect. I then returned the trigger level to full + ( clockwise ), attenuator down to 50mv, and with the waveform filling the screen, I got trigger lock. I did note, that during the modified 5-40 calibration attempt, there was no sign of the trigger signal with TRIG VIEW depressed. However, with the intentional misadjustments reported above, I could just see some light at the top of the screen in TRIG VIEW. Although I was advised not to start messing with anything but R565, I adjusted R534 in the "misadjusted" state using TRIG VIEW. The waveform came into view, and I could center it. With this set of adjustments, I could now trigger on the 12mv waveform
> > > > >with the attenuator turned up to .1v so that I could meet the .32 divisions performance called out in 5-40. I thought I was on to something regarding the trigger centering. I esr'ed all the electrolytics in the triggering section. All checked out. A separate check with a VOM didn't show shorted electrolytics. I thought there may be a fault with U520, and given both it, and U720 were both socketed, I swapped them. No change. I haven't been able to find any shorted bypass caps..yet. I replaced Q532, and two resistors that were more than 50% out of spec. No go. One thing that bothers me is that, on the schematic, the emitter of Q532, is pulled up through R535 to +8.2v. I only measure +5.0v. I can't find any errata that verifies my measurement. The 8.2v source is functioning as it is available everywhere else noted on partial A8 schematic with trigger circuit. Trigger level at pin 14 of U520 varies from 1.7v (full + level) to 200mv (full - level). Is this OK? TP526 has a copy of the 12mv
> > > > >waveform as expected. I'm fixated on the centering circuit, but can go no further. With HORIZ DISPLAY on A LOCK, there shouldn't be any interaction with TRIG B? Right? I suppose trimmer 534 could be bad, but checking that out requires flipping A8. Yeesh! I haven't messed with R673 yet, as my troubleshooting has been with AC coupling only. Should I go there?
> > > >
> > >
> >
>


 

I am a little surprised that the A trigger centering adjustment could
not calibrated that offset out but with Q522 bad, the trigger
sensitivity could have been screwed up anyway.

Do you have any idea if the tunnel diodes you replaced were bad as
well? I have an idea for how to replace the tunnel diodes used in the
465/475 trigger circuits with 3 transistors each but will need to pick
up a broken oscilloscope to try it out.

I have a nice copy now of the 475 schematics in my notebook. I just
need to find some 465 schematics I can clean up. I noticed that the
465 schematics have more diagnostic notations like voltages and
waveforms than the 475 schematics.

On Mon, 25 Feb 2013 01:21:44 -0000, "stan_katz" <stan_katz@...>
wrote:


SOLVED...while pin 3 of U520 had a good copy of the waveform being triggered on, the DC voltage on pin 3 was 1.6v. I found the U520 pin voltages posted by Tom Miller and noted that proper voltage for pin 3 should be .7v. In addition, the base of Q526 had almost 1 volt on it. Not right! I don't have a curve tracer but a simple DMM probing of the diff amp JFETS proved Q522 was blown. Ordered another matched pair and my 475 is back on the air. Now...with all my troubleshooting cal. tweaks behind me, this scope can really use a good calibration. Whew!

Thanks - Tom, David, Max, Albert, et.al
Stan

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@...> wrote:

OK, glad to hear that!

Raymond

--- In TekScopes@..., "stan_katz" <stan_katz@> wrote:

I purchased original NOS Tektronix p/n tunnel diodes listed in the 475 manual.

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

I haven't followed this thread but noticed that you purchased new TD's and as David says, your adjustments seem to be (quite far) off.
Did you purchase the right TD's? They're not all the same!
Peak currents vary from 1mA to more than 10mA. They need appropriate biase adjustments!

Raymond

--- In TekScopes@..., David <davidwhess@> wrote:

If those low profile socket elements are the ones I am thinking of,
they are called Miniserts. I have had at least two incidents now
where a Minisert was open and reseating the lead at least temporarily
fixed the problem.

There is a datasheet for them in the files area:

http://f1.grp.yahoofs.com/v1/5EskUWIwdScdLDCLRHNKBOlgfv-EbF0Km21vDCqeT_vx9Vh_SFUazvNofOxE469fMyGLxa74BOyQSCw8uTjrptaMWNJNuWVtKXJ4M4LBses/Minisert.pdf

Q532 (and Q526) are operating as emitter followers. The emitter
voltages for each are low impedance and should be about 0.6 volts
higher than their base voltages at all times. They are just used as
simple voltage buffers.

Trigger B is completely independent from trigger A and is only used if
a sweep mode other than A internal is selected.

From your description I suspect everything is working but that the A
trigger circuit needs to be calibrated:

R534 is used to center the trigger point vertically on the CRT when
R530 is in the middle of its rotation.

R673 adjusts the trigger view vertical positioning on the CRT.

R547 adjusts the trigger level so that it does not change when the
slope is changed.

R565 adjusts the tunnel diode threshold for maximum sensitivity.


stan_katz
 

David,

I suspect the tunnel diodes were ok, since replacing them didn't change any symptoms or offsettings needed to compensate. I really don't want to put the originals back in to find out since this 475 is lousy with sockets for semis including the tunnel diodes. Every insert, and removal brings a socket (aka minisert as you call them) closer to its end-of-life. I'll leave well enough alone for now.

Stan

--- In TekScopes@..., David <davidwhess@...> wrote:

I am a little surprised that the A trigger centering adjustment could
not calibrated that offset out but with Q522 bad, the trigger
sensitivity could have been screwed up anyway.

Do you have any idea if the tunnel diodes you replaced were bad as
well? I have an idea for how to replace the tunnel diodes used in the
465/475 trigger circuits with 3 transistors each but will need to pick
up a broken oscilloscope to try it out.

I have a nice copy now of the 475 schematics in my notebook. I just
need to find some 465 schematics I can clean up. I noticed that the
465 schematics have more diagnostic notations like voltages and
waveforms than the 475 schematics.

On Mon, 25 Feb 2013 01:21:44 -0000, "stan_katz" <stan_katz@...>
wrote:


SOLVED...while pin 3 of U520 had a good copy of the waveform being triggered on, the DC voltage on pin 3 was 1.6v. I found the U520 pin voltages posted by Tom Miller and noted that proper voltage for pin 3 should be .7v. In addition, the base of Q526 had almost 1 volt on it. Not right! I don't have a curve tracer but a simple DMM probing of the diff amp JFETS proved Q522 was blown. Ordered another matched pair and my 475 is back on the air. Now...with all my troubleshooting cal. tweaks behind me, this scope can really use a good calibration. Whew!

Thanks - Tom, David, Max, Albert, et.al
Stan

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

OK, glad to hear that!

Raymond

--- In TekScopes@..., "stan_katz" <stan_katz@> wrote:

I purchased original NOS Tektronix p/n tunnel diodes listed in the 475 manual.

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

I haven't followed this thread but noticed that you purchased new TD's and as David says, your adjustments seem to be (quite far) off.
Did you purchase the right TD's? They're not all the same!
Peak currents vary from 1mA to more than 10mA. They need appropriate biase adjustments!

Raymond

--- In TekScopes@..., David <davidwhess@> wrote:

If those low profile socket elements are the ones I am thinking of,
they are called Miniserts. I have had at least two incidents now
where a Minisert was open and reseating the lead at least temporarily
fixed the problem.

There is a datasheet for them in the files area:

http://f1.grp.yahoofs.com/v1/5EskUWIwdScdLDCLRHNKBOlgfv-EbF0Km21vDCqeT_vx9Vh_SFUazvNofOxE469fMyGLxa74BOyQSCw8uTjrptaMWNJNuWVtKXJ4M4LBses/Minisert.pdf

Q532 (and Q526) are operating as emitter followers. The emitter
voltages for each are low impedance and should be about 0.6 volts
higher than their base voltages at all times. They are just used as
simple voltage buffers.

Trigger B is completely independent from trigger A and is only used if
a sweep mode other than A internal is selected.

From your description I suspect everything is working but that the A
trigger circuit needs to be calibrated:

R534 is used to center the trigger point vertically on the CRT when
R530 is in the middle of its rotation.

R673 adjusts the trigger view vertical positioning on the CRT.

R547 adjusts the trigger level so that it does not change when the
slope is changed.

R565 adjusts the tunnel diode threshold for maximum sensitivity.


Brian Carter
 

...and I just stopped by to say: that person is me. {8^>)

I have therefore stopped in and joined the group to say thank you, Stan, for posting all this, and thanks to all of you; to Tom I say: you were right. I couln't believe I found this slightly arcane information. In the process, I've learned *not to touch* those tunnel diodes.

I have a 475, on which the trigger control has been drifting for a few years, requiring a more greater and greater excursion clockwise to obtain a stable trigger. Not a problem for a while, but the most recent time I fired it up, it seemed so far off the mark that I finally decided to have a good sit-down with the manual to see what might be going on. Of course, I first tried the trigger centering pot, but it, too, wound up in a far-clockwise excursion, to little effect.

I traced the problem down to having 1.4-ish volts on pins 3 and 14 of U520, instead of 0.7v as called out in the manual. The "B" trigger works as expected, is just about identical, and it has 0.7v on those pins. How this had happened, and why, was a bit beyond me. I was unsoldering resistors, thinking they'd drifted and left a transistor's bias all wrong. No dice there.

Well, then I found this thread, and here I am, "someone" seven years "in the future", benefitting from Stan's work.

Thanks again guys. My 475 was military surplus and from a pretty late production run (the manual is dated 1977), purchased from eBay for a great price, and the thing is just nearly pristine. I really lucked out. But then I'd been looking for a really nice 465 or 475 for a good while, having bought a 531 from a really nice fella in 1997 or so for $50.

Yes, the 531 still works, and works quite well.

bc