Date   

Re: 465/475 Volts/Div range LED swap problem.

Dave Peterson
 

Yep, just found the horizontal amp you sent. Too perfect. This is exactly what I was working toward:

I have the 465 Wes Bolin was working on for his friend in the garage. I'm going to try my hand at resuscitating it, and having a simulation to get to know the circuit will be a huge help. Starting with a simple circuit like the Probe Indicator was a perfect introduction.

Wes did a single PS cap fix, but I have a left over set of adapters and caps from doing a PS cap update on another parts scope. So I think first I'm going to do the full swap on it first. It'll be a bit before I can share the goings on with the horizontal amp. But I will when I get there.

Dave

On Saturday, February 20, 2021, 03:09:56 PM PST, Ozan <ozan_g@erdogan.us> wrote:

Hi Dave,
I look at the messages between tasks and usually on a small screen so my replies are usually on the short side. I hope it doesn't come out as terse. I like these puzzles, keep them coming.

Wouldn't the low R win over the LED and keep it weak/off?
The bulb must be consuming >50mA and your LED is probably consuming ~ 20mA so we can burn another 10mA without overloading the Darlington. On the other hand R has to be small enough to keep the LED off. Exact value is not critical but 470-ohm would work.

I spent a good amount of time yesterday and this morning coming up to speed on
LTSpice. For example, I needed to figure out how to add a Darlington pair for
I remember sending you an example LTspice schematic. Looks like you find it useful too, it is a great free tool.

Ozan


Re: 2467B TEST 04 FAIL 02

Thomas Voshell
 

Thanks Jon & Chuck,

I have made some progress: Now I am passing my cals. It helps a lot to have marker signals of an appropriate amplitude for the routines to sample.
Now I have another issue that was waiting for me all along. I am getting a “CT TEST 81 FAIL 03” . I believe CT means Confidence Test but I am not sure. Regardless, I am not finding the meaning of 81 with 03.

Does anyone have an idea about this one?

I cannot seem to find any info about 80 series CT tests.


Thanks,
-TomV


Re: 3T77 tunnel diodes (again)

Tom Lee
 

That 2N1516 is almost certainly afflicted with the tin whisker problem, as are basically all devices in a TO-7 (and others whose cans are substantially of tin). The case is likely showing a short to one or more of the terminals. It's often temporarily fixable with a capacitive discharge, but just for grins and giggles, not as a repair.

From a quick glance at the circuit, it looks like a garden-variety silicon PNP should get the job done. Try a 2N3906 if you have one handy.

Look forward to hearing how that works out.

--Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 2/20/2021 16:56, Charles wrote:
I did some more digging in my junkbox and discovered a Tek-numbered bag also labeled "10 ma tunnel diode" :) so I won't have to wait two months for the Russian TDs. It has wire leads (the tiny "top hat" case), but that will certainly work for now - I can make them quite short for a permanent install later. I tested it and it switches at 8.9 ma.

Then I played with the resistor values in the D42 trigger regen circuit. Doubling R43 (300 ohm) didn't give me enough range to get to 8-9 ma on R44 (200 ohm pot). Ended up with 150 ohms in series with R43. I next increased R41 from 5.1 ohm to 10 ohm, adjusted R44 and a nice trigger output appeared at the front panel jack! Good pulses also coming out of Q94 which provides the staircase advance pulse and sampling drive to the 3S2.

I next removed the BSM connector (trigger out) from the 3S2 front panel and replaced it with a solderable SMA. I ran a cable from there to the ext trig input on the 3T77A. At this point I had sampling dots appearing on the screen - but no sweep (i.e. a messy vertical line). It moves horizontally with the position control and adjustments so the output stages are working. Tracked the pulse train down through Q124 ok, but it disappears at the base of Q135 completely, and of course nothing on Q135 collector. It's not shorted to a simple diode-function check B-E or B-C on my Fluke 73, nor is D134 (reverse-bias protection from B-E). But when I pull Q135 from its socket, the signal comes back there...

Now I need to dig out a PNP Ge switching transistor that can withstand at least 25 volts Vce to substitute for this 2N1516... I tried a handy 2N414 but it didn't work. Turns out its Vce of 15v is lower than the -20v power supply... oops. Also it's slower (7 MHz vs. 35 which may not be needed). I think a silicon PNP will also work there, which greatly increases the choices - I will just have to experiment.

This thing is absolutely stuffed with tunnel diodes... sure hope the rest are ok.




Re: 3T77 tunnel diodes (again)

 

I did some more digging in my junkbox and discovered a Tek-numbered bag also labeled "10 ma tunnel diode" :) so I won't have to wait two months for the Russian TDs. It has wire leads (the tiny "top hat" case), but that will certainly work for now - I can make them quite short for a permanent install later. I tested it and it switches at 8.9 ma.

Then I played with the resistor values in the D42 trigger regen circuit. Doubling R43 (300 ohm) didn't give me enough range to get to 8-9 ma on R44 (200 ohm pot). Ended up with 150 ohms in series with R43. I next increased R41 from 5.1 ohm to 10 ohm, adjusted R44 and a nice trigger output appeared at the front panel jack! Good pulses also coming out of Q94 which provides the staircase advance pulse and sampling drive to the 3S2.

I next removed the BSM connector (trigger out) from the 3S2 front panel and replaced it with a solderable SMA. I ran a cable from there to the ext trig input on the 3T77A. At this point I had sampling dots appearing on the screen - but no sweep (i.e. a messy vertical line). It moves horizontally with the position control and adjustments so the output stages are working. Tracked the pulse train down through Q124 ok, but it disappears at the base of Q135 completely, and of course nothing on Q135 collector. It's not shorted to a simple diode-function check B-E or B-C on my Fluke 73, nor is D134 (reverse-bias protection from B-E). But when I pull Q135 from its socket, the signal comes back there...

Now I need to dig out a PNP Ge switching transistor that can withstand at least 25 volts Vce to substitute for this 2N1516... I tried a handy 2N414 but it didn't work. Turns out its Vce of 15v is lower than the -20v power supply... oops. Also it's slower (7 MHz vs. 35 which may not be needed). I think a silicon PNP will also work there, which greatly increases the choices - I will just have to experiment.

This thing is absolutely stuffed with tunnel diodes... sure hope the rest are ok.


Re: TM500 Mainframe Tester construction master thread.

Dave Seiter
 

I finished my unit and then discovered that the +15V didn't work.  Took about 2 minutes of head scratching before I realized I hadn't soldered the connections for that binding post, the scope output and one of the phase LEDs....


Re: TM500 Mainframe Tester construction master thread.

Dave Seiter
 

I ran across number 2 also, but the knob I decided to use had two set screws, so I tightened the one on the round portion first, then the one on the flat section.  It's not bullet proof, but it will work. 
-Dave

On Saturday, February 20, 2021, 11:13:34 AM PST, Andy Warner <andyw@pobox.com> wrote:

So far, I have one observation, and one question:
1. observation - digikey BOM has a typo in the reference designators for the 1N4007 diodes. "CR11" should read "CR101".
2. question - if I insert the stops in S3 where the manual suggests on page 2, the index on the knob does not align with the front panel when using the flat on the shaft with the grub screw.
              I plan on buzzing the switch out to see what the correct location is, but I thought I would ping the list about the inconsistency as well.

--
Andy


Re: P6021 Noise Problem?

Chappy
 

No but I do live next to a military base, and I am about 4000ft away from an air traffic control surveillance radar. You may be on to something there. Is it possible that the high frequency FET and transistors are picking this up? It has not been giving me a problem with my lower frequency probes.

I will try to get some screen shots posted later.

Thanks for the help so far.

Sincerely,
Steve


Re: 465/475 Volts/Div range LED swap problem.

Dave Peterson
 

Ozan,

Ah, you're who sent the LTSpice reference. Yeah, thanks so much. It's simplistic, but does everything it needs to do. I can live with rotate-mirror-rotate vs. vertical-flip. BFD. I love simple.

It also correlates with measured very well.

I have not mastered concise. I admire terse that gets the message across. Your input is always spot-on. Keep it coming!

Dave

On Saturday, February 20, 2021, 03:09:56 PM PST, Ozan <ozan_g@erdogan.us> wrote:

Hi Dave,
I look at the messages between tasks and usually on a small screen so my replies are usually on the short side. I hope it doesn't come out as terse. I like these puzzles, keep them coming.

Wouldn't the low R win over the LED and keep it weak/off?
The bulb must be consuming >50mA and your LED is probably consuming ~ 20mA so we can burn another 10mA without overloading the Darlington. On the other hand R has to be small enough to keep the LED off. Exact value is not critical but 470-ohm would work.

I spent a good amount of time yesterday and this morning coming up to speed on
LTSpice. For example, I needed to figure out how to add a Darlington pair for
I remember sending you an example LTspice schematic. Looks like you find it useful too, it is a great free tool.

Ozan


Re: P6021 Noise Problem?

Jean-Paul
 

Send scope shots of noise with scale factprs and sketch of entirely setup eg 50 ohm term at scope or1 m?

probe tip open or shorted to grd ring etc.

Check service manual for noise test conditions

Could be bad FET or failed bypass caps.

Jon


Re: 465/475 Volts/Div range LED swap problem.

Ozan
 

Hi Dave,
I look at the messages between tasks and usually on a small screen so my replies are usually on the short side. I hope it doesn't come out as terse. I like these puzzles, keep them coming.

Wouldn't the low R win over the LED and keep it weak/off?
The bulb must be consuming >50mA and your LED is probably consuming ~ 20mA so we can burn another 10mA without overloading the Darlington. On the other hand R has to be small enough to keep the LED off. Exact value is not critical but 470-ohm would work.

I spent a good amount of time yesterday and this morning coming up to speed on
LTSpice. For example, I needed to figure out how to add a Darlington pair for
I remember sending you an example LTspice schematic. Looks like you find it useful too, it is a great free tool.

Ozan


Re: P6021 Noise Problem?

Tom Lee
 

Do you live relatively near to an FM radio station?

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 2/20/2021 13:08, Chappy wrote:
I recently acquired a P6201 active 1X FET probe which appears to have never been used. The inspection tag was still attached, the accessory pack was still sealed, and there was not a single mark on the probe's ground sleeve. All functions of the probe are working but it has a 2mVpp high frequency noise component riding on any signals that I measure.

The manual states a 'Noise Tangental' of 300uV (150uV RMS), a figure well below the noise signal that I am seeing.

I have tried the probe on both my 7403 through a 7A18, and a new Keysight DSOX1102G with the same results. I have tried powering the device with a Tektronix bench power supply, and a home made unit with the same results. Interesting thing is that the noise level riding on the signal is almost non existent when I feed it a supply of +/- 5V. As I increase the supply voltage above this the noise becomes more apparent. Based on this observation I believe that i can rule out noise picked up by the cable between the amplifier and the probe. I have also scoped the power supply rails with negligible abberations on the supply traces on a 2mv/div scale. With the Keysight scope (BW = 70Mhz) a screen capture shows that the lowest component of the noise starts at approx 100MHz.

I am starting to think that there may be components inside either the amp or probe that have degraded over time. Could a degraded or failed electrolytic capacitor contribute to this noise? Or could it be due to a damaged FET or BJT?

If anyone here has one of these I would welcome your input before I go chasing a problem which perhaps is completely normal for this probe. Once again, its physical appearance indicated that it has never (or hardly) been used.

Sincerely,
Steve








TM500 Tester Board Set Deliveries

Larry McDavid
 

I just checked the UPSP tracking info for all the tester board set shipments mailed on 2/11/2021 and find the following on 2/20/2021:

1. All but one USA shipments are delivered

2. One USA shipment to Florida is in Orlando, Florida today, 2/20/21

3. Two shipments to Alberta, Canada were in Seattle, Washington on 2/18/21.

4. One shipment to Quebec, Canada was delivered 2/16/21

5. One shipment to Frankford, Germany was in Frankford on 2/14/21

6. Four shipments to UK were delivered 2/17 and 2/18/21

7. One shipment to Kenilworth, UK is in transit 2/18/21

8. One shipment to Australia was delivered 2/19/21

9. Two shipments to Australia are in transit 2/16 and 2/19/21

10. Two shipments to France are in transit 2/15/21

11. One shipment to Ireland is in Dublin 2/14/21

12. One shipment to Spain is in Madrid 2/15/21

I don't know what the delay in the one shipment to Florida is. Maybe weather... Gosh, there has been a lot of cold and snow out there!

The USPS tracking of international shipments has little international detail but at least some show delivered so USPS gets some feedback. I don't know if that is true for all countries.

I suggest all who have not yet received the board sets wait until mid next week. If you still don't have the package, send me a private email and I'll provide the tracking number.

The package is 13 x 10 inches in a flat mailer and won't bend in normal handling. Some have reported the postal carrier has rung the doorbell and left the package. So, this package may not fit in a standard mail slot or mail box.

Many have reported successful delivery to me and all have said the boards arrived in good condition.

A comment: Dennis Tillman, based on his experience shipping the many CRT books, suggested I ask for an emailed postal receipt with tracking numbers. That was a great idea! If you ship numerous packages at once, do use the USPS email receipt capability. The tracking numbers on that emailed receipt are actually hyperlinks, making tracking easier. I was unaware of that capability and I expect others are also unaware.

Weather can wreak havoc on all kinds of deliveries. Local COVID vaccination sites have been shut down for days due to non-local weather-induced vaccine deliveries.

One mailer was delivered in one day; many were delivered in two days. I believe we've got a great post office!

--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)


Rather than a TM500 module extender....

 

I just want to mention again that all the issues raised with regard to module extenders are important,
and no matter which route you go, the result is always a bit sub-optimal, and awkward on the bench

The magic answer is just to take a TM502A apart, removing the blue outer shell. What's left is a compact dual connector power supply (complete with power switch + line connector), and total access to the module under test. This is the simplest, easiest, and most trouble free way to work on a TM500 plug in, and takes up the least possible bench space. I highly recommend this path over all others. A similar trick is possible with a TM5003 for the TM5000 modules, but it's certainly bigger.

I should point out that I did not move to this approach until long after I already had many extenders, and it's only this specific frame that yields such good results. In any case, it is a magical fix, full of test bench happiness.

Test plug-ins to validate the frame are still needed, and you may still want to extend a plug in from a specific frame, so that's the best case for an extender.

All the best,
walter (walter2 -at- sphere.bc.ca)


P6021 Noise Problem?

Chappy
 

I recently acquired a P6201 active 1X FET probe which appears to have never been used. The inspection tag was still attached, the accessory pack was still sealed, and there was not a single mark on the probe's ground sleeve. All functions of the probe are working but it has a 2mVpp high frequency noise component riding on any signals that I measure.

The manual states a 'Noise Tangental' of 300uV (150uV RMS), a figure well below the noise signal that I am seeing.

I have tried the probe on both my 7403 through a 7A18, and a new Keysight DSOX1102G with the same results. I have tried powering the device with a Tektronix bench power supply, and a home made unit with the same results. Interesting thing is that the noise level riding on the signal is almost non existent when I feed it a supply of +/- 5V. As I increase the supply voltage above this the noise becomes more apparent. Based on this observation I believe that i can rule out noise picked up by the cable between the amplifier and the probe. I have also scoped the power supply rails with negligible abberations on the supply traces on a 2mv/div scale. With the Keysight scope (BW = 70Mhz) a screen capture shows that the lowest component of the noise starts at approx 100MHz.

I am starting to think that there may be components inside either the amp or probe that have degraded over time. Could a degraded or failed electrolytic capacitor contribute to this noise? Or could it be due to a damaged FET or BJT?

If anyone here has one of these I would welcome your input before I go chasing a problem which perhaps is completely normal for this probe. Once again, its physical appearance indicated that it has never (or hardly) been used.

Sincerely,
Steve


Re: 465/475 Volts/Div range LED swap problem.

Dave Peterson
 

There are many facets to this experience for me:

One is that I want this info in the groups messages in the hope that it might help others in the future. So pardon if this is rudimentary for the more experienced of the group.

Another is that I wanted to reeducate myself in BJT circuits. I haven't dealt with them since school. This has been a great experience.

It was actually the thought of adding a parallel resistor to the 10X led/resistor to provide an alternate current path that led me to using a NPN. I wasn't sure what was going to happen when Q382 tried to drive the 10X LED. Wouldn't the low R win over the LED and keep it weak/off? I didn't have LTSpice setup yet. So I thought, since I'd just gotten this load of NPNs, why not? And down the Rube Goldberg path I went.

The NPN does end up with an elevated base voltage when 10X is on and 1X is off. It doesn't effect the 1X diode, but it is dangerously close to turning on.

Now that I have the simulation set up I was able to test the 470 ohm resistor, and sure enough, it works great. See, I knew I was making it more complicated than need be. Simplicity is definitely what I was trying to accomplish.

I spent a good amount of time yesterday and this morning coming up to speed on LTSpice. For example, I needed to figure out how to add a Darlington pair for Q382. As well as the simple things too. In fact I started with two 2N2907's as my Q382 at first. Worked pretty well, and got me up to speed enough to tackle the next level exercise of adding a third party model (and make it portable too).

I'm not very good at learning a new tool in a purely academic way - even if it is very similar to what I've used before. I need something practical to apply it to. This was a perfect circuit to cut my teeth on. Thanks to all who suggested it before. Was that you Michael? It has now also been a good exercise in finding minimal solutions. I also now have a better model to test on than a bread board with too few components.

I don't think I'll ever be up to speed on these scopes and circuits as so many of you. But I am learning, and very much enjoying myself.

Thanks to all who tolerate me and help.
Dave


On Saturday, February 20, 2021, 11:14:07 AM PST, Ozan <ozan_g@erdogan.us> wrote:


decided to wire one parallel to the 10X LED. I was really trying to minimize
the complexity of this solution. This was the best I could come up with.
See my reply https://groups.io/g/TekScopes/message/179044
A 470-ohm from collector of the Darlington to ground (across the LED+current limiting resistor) is all you need. No need for ten LEDs in parallel, and it is not the most robust solution either.

Ozan


Re: 2467B TEST 04 FAIL 02

Jean-Paul
 

Tom V

the steps are divided into sections and each type of CAl is independent of the other sections.

Certain steps near the end require a very precise and symmetric test wave in both amplitude and frequency.

If you dont generate that précise signal, the CAL of that step will fail.

I think Chuck will recall previous discussions, but I forgot which CAL it was, perhaps the HOR.

It was the only step that is is so picky.

Jon


Re: Failed Transistor with Low h(FE)?

Ed Breya
 

Chuck wrote: "No wonder HP only used 1% or better parts"

Haha - I wouldn't be too surprised if there's a hole in the middle of those too, where the 0.1 % tolerance grade parts are "pre-removed" for your convenience. It depends on how far you need to, and can, grade parts from a given process, and on the economic value of doing so.

Ed


Re: 465/475 Volts/Div range LED swap problem.

Ozan
 

decided to wire one parallel to the 10X LED. I was really trying to minimize
the complexity of this solution. This was the best I could come up with.
See my reply https://groups.io/g/TekScopes/message/179044
A 470-ohm from collector of the Darlington to ground (across the LED+current
limiting resistor) is all you need. No need for ten LEDs in parallel, and it
is not the most robust solution either.
I now see the solution, 10x was just the label, not the number of LEDs. No need for extra transistor, 470-ohm is all you need. Sim might have worked OK but in the proposed solution base of the new NPN is not pulled to ground strongly so noise could couple to the base easily.

Ozan


Re: 465/475 Volts/Div range LED swap problem.

Ozan
 

decided to wire one parallel to the 10X LED. I was really trying to minimize
the complexity of this solution. This was the best I could come up with.
See my reply https://groups.io/g/TekScopes/message/179044
A 470-ohm from collector of the Darlington to ground (across the LED+current limiting resistor) is all you need. No need for ten LEDs in parallel, and it is not the most robust solution either.

Ozan


Re: TM500 Mainframe Tester construction master thread.

Andy Warner
 

So far, I have one observation, and one question:
1. observation - digikey BOM has a typo in the reference designators for the 1N4007 diodes. "CR11" should read "CR101".
2. question - if I insert the stops in S3 where the manual suggests on page 2, the index on the knob does not align with the front panel when using the flat on the shaft with the grub screw.
I plan on buzzing the switch out to see what the correct location is, but I thought I would ping the list about the inconsistency as well.

--
Andy

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