Date   

Re: 485 super weak brightness control

Ozan
 

This is exactly what I observed on A gate and A sweep, I haven't checked
the B sweep connector
I attached expected waveform here:
https://groups.io/g/TekScopes/photo/262059/0?p=Created,,,20,2,0,0
If it looks similar then B gate delay is OK, if B gate is delayed issue is around U910/Q902.

In the last paragraph you mentioned 2x multiplier but what we observe is
10x, does it still make sense to look in this part of the circuit?
You are right. However, I can't think of a simple reason why 0.2us-10us range could be 10x slower in B sweep while 1ns-0.1us is OK (please confirm this range is OK). K1242 switches at 0.2us step. Perhaps time to look at that relay and measure cap C1443.

Are you sure B sweep shaft is not rotated out of alignment? You can look at J1 (relay signal) and check it switches at .1us/.2us boundary.

If the gate signal matches the waveform I sent and you still see trace shifted right, checking B18,B20, B22 can tell if anything is wrong with B sweep horizontal shift circuit. These switches should make contact in 1/2/5n so if they are dirty you could see horizontal shift issues.

Ozan


7A16A high frequency compensation.

unclebanjoman
 

Hi all,

I've recently purchased a 7A16A, working, looks new, S/N B138015.

Probably the previous owner has tried to calibrate the HF response in a badly manner: risetime was 3 ns with very rounded front corners.
Suspecting a strong misadjustment of HF compensation, I did a full calibration procedure.

Problem: I'm unable to obtain a decent compromise between risetime and flat-top and square corner.

I'm using a PG506, a Type 111 and 7854 mainframe. 7A16A in the left compartment, no extender.

Following the procedure as per manual, I spent 4 hours trying to calibrate the best, but the various settings interacts with each other and I'm unable to obtain a decent rising edge.
Sometimes the rising edge is distorted in the middle of the front. Other time there is an auto-oscillation. Touch one trim and the waveform gets better. I touch another one and the waveform gets worse.
I heard that the calibration procedure was tricky, but I have never encountered a difficulty like that.
All resistive and capacitive trimmers are O.K, perfectly functional.

Does anyone know a better procedure than the (fairly simplistic) one outlined in the manual?
Moreover, in the manual there is not even a photograph of some typical waveform that can be used as a reference. Does anyone know where to find a screenshot of a typical 7A16A step response?

Cheers,
Max


Re: TDS544A with strange display #photo-notice

durechenew@...
 

Some news, but not what you may expect.
As there were some doubts (and I agree, for good reasons), I opened the display area again; soldered two wires to shutter connections - totally random, I have no idea for which colors and I believe it's not relevant. Shutter connector in normal place, put everything back and started the scope. Here is the moment to say, for Siggi, that drivers for the shutter are indeed powerful, initially designed to drive (servo) motors at 20kHz, max 0.5A DC.
OK, see pictures 5 to 8 in the album.
Synchro signal on Ch1, frame, as I said before, around 17 ms (by signal I mean waveform).
Picture 5: on Ch2 (should be green but, at low light, camera doesn't make much of a difference between colors) is signal from output of driver for one of the shutter's colors.
Picture 6: same signals, different timing.
Picture 7: same as 6 but signal is displayed on Ch4, not Ch2. Some vertical vectors are obviously of different color (naked eye sees clear red). If Ch4 light is OFF (pressing Ch1, for example) signal is all blue (no red vectors).
Picture 8: Same as Picture 6, different shutter channel ( different driver output/color).
Conclusions:
1. Shutter works fine; period of signal, roughly 370uS or so (just to have an idea how often the shutter refreshes the colors - definitely not line frequency). As I don't have the pair signal for the same color I cannot say if they are really opposite; it may be that some time they are not (and that color is not ON), depends how the control signals come from the memory.
2. Some waveform information for Ch4 is incorrectly displayed when a different color (driver output for red) is ON (and on condition that light of Ch4 is also ON). This back the same conclusion it was suggested before: Between the point(s) of split from VGA the signal path toward Video for CRT is corrupted. Still to be discovered where and how...
TT


Re: How to troubleshoot a faulty 7B92A?

Harvey White
 

The horizontal line is generated, of course, by the 7B53.  That the line is in the middle or can be adjusted so suggests that the position control and circuitry into the frame is working.  Now what doesn't work in the vertical compartment would be blanking, which would make no sense to have.

What I suspect is that the sweep is never triggering, remains in a holdoff state.  That would blank the display, which I think you see.

I'd be looking at the sweep.

Harvey

On 3/19/2021 4:56 PM, Thierry Delaitre via groups.io wrote:
thanks both

I've tried putting the 7B92A into the left vertical slot

I can see a horizontal line which I can move up and down using the position button of the 7B92A

There is no sweep coming up. the line remains horizontal

Thanks

Thierry





Re: 485 super weak brightness control

Ondrej Pavelka
 

In the last paragraph you mentioned 2x multiplier but what we observe is
10x, does it still make sense to look in this part of the circuit?

On Fri, 19 Mar 2021, 22:47 Ondrej Pavelka, <info@vintageaudiorepairs.eu>
wrote:



On Fri, 19 Mar 2021, 22:18 Ozan, <ozan_g@erdogan.us> wrote:

I noticed when I move the picture all the way to the left in 521 mode
there
is something on the screen but it's all crooked
I can think of two possibilities: B sweep delay is not reset to zero in
5/2/1n mode (there is a circuit to do that), or there is a little circuit
that shifts the screen left in B sweep mode (Q1331 in <11>) that is not
working
Great feedback, I will check this out on Monday


Delay not set to zero:
In 5/2/1n mode B timebase is used but delay is set to zero. It could be
that the delay is applied still because of some issue. On <7> switch A9
opens in 5/2/1n mode to set time delay zero independent of delay knob. It
is possible the delay pot is dirty and not making a good contact. What
voltages do you see at pin 3 of U910 and base of Q902B in 5/2/1n mode?

I don't think pot is dirty because I can smoothly and without any jumping
adjust delay on the presets where I can see both A and B sweeps



B sweep shift:
B18, B22, B1-4, control left shift of trace in B sweep. You can check B18
and B22 by measuring voltages at J3 and J5 on sheet <11>

Great suggestion, I will check that on Monday


I looked at A sweep, A gate, and B gate signals on my 485. A sweep and A
gate signals stay same as 10ns setting when you are in 5/2/1n. When in A
sweep B gate is not there until you hit 5/2/1n, then B gate starts at the
same time as A gate (zero delay).
This is exactly what I observed on A gate and A sweep, I haven't checked
the B sweep connector


I remember you didn’t see A gate in 5/2/1n. Could you re-measure again
between 10ns and 5ns settings? May be "B ends A" is active although 5/2/1n
should turn it off. On front panel you will see “B ends A” next to the
hold-off knob. Does it make any difference if it is not in “B ends A”? If
it does A2 switch on <9> is dirty.
That is not correct, I was able to see the gate signals but they only
haven't changed. Same as you described above


B sweep in the positions 10us to 0.2us is showing it 10x wrong
I read as B sweep runs slower.

Correct



So 100ns is shown as 1us
Is 0.1us also 10x slower? Above statement was for 10us to 0.2us.
I used bad example time, I wanted to make sure we know in which direction
slower / faster


How is 2ms, is it also 10x slower?
I can't see it so I can't tell you, long times are not showing me anything
then I have a set of times which are shown as slow then I get correct times
but truncated


You may want to check relay K1241, caps C1443, C1442.

Switch B18 turns on a 2x multiplier, if it is not working you will get 2x
slower.

Good one I'll check that



Ozan






Re: 485 super weak brightness control

Ondrej Pavelka
 

On Fri, 19 Mar 2021, 22:18 Ozan, <ozan_g@erdogan.us> wrote:

I noticed when I move the picture all the way to the left in 521 mode
there
is something on the screen but it's all crooked
I can think of two possibilities: B sweep delay is not reset to zero in
5/2/1n mode (there is a circuit to do that), or there is a little circuit
that shifts the screen left in B sweep mode (Q1331 in <11>) that is not
working
Great feedback, I will check this out on Monday


Delay not set to zero:
In 5/2/1n mode B timebase is used but delay is set to zero. It could be
that the delay is applied still because of some issue. On <7> switch A9
opens in 5/2/1n mode to set time delay zero independent of delay knob. It
is possible the delay pot is dirty and not making a good contact. What
voltages do you see at pin 3 of U910 and base of Q902B in 5/2/1n mode?

I don't think pot is dirty because I can smoothly and without any jumping
adjust delay on the presets where I can see both A and B sweeps



B sweep shift:
B18, B22, B1-4, control left shift of trace in B sweep. You can check B18
and B22 by measuring voltages at J3 and J5 on sheet <11>

Great suggestion, I will check that on Monday


I looked at A sweep, A gate, and B gate signals on my 485. A sweep and A
gate signals stay same as 10ns setting when you are in 5/2/1n. When in A
sweep B gate is not there until you hit 5/2/1n, then B gate starts at the
same time as A gate (zero delay).
This is exactly what I observed on A gate and A sweep, I haven't checked
the B sweep connector


I remember you didn’t see A gate in 5/2/1n. Could you re-measure again
between 10ns and 5ns settings? May be "B ends A" is active although 5/2/1n
should turn it off. On front panel you will see “B ends A” next to the
hold-off knob. Does it make any difference if it is not in “B ends A”? If
it does A2 switch on <9> is dirty.
That is not correct, I was able to see the gate signals but they only
haven't changed. Same as you described above


B sweep in the positions 10us to 0.2us is showing it 10x wrong
I read as B sweep runs slower.

Correct



So 100ns is shown as 1us
Is 0.1us also 10x slower? Above statement was for 10us to 0.2us.
I used bad example time, I wanted to make sure we know in which direction
slower / faster


How is 2ms, is it also 10x slower?
I can't see it so I can't tell you, long times are not showing me anything
then I have a set of times which are shown as slow then I get correct times
but truncated


You may want to check relay K1241, caps C1443, C1442.

Switch B18 turns on a 2x multiplier, if it is not working you will get 2x
slower.

Good one I'll check that



Ozan






Re: 485 super weak brightness control

Ozan
 

I noticed when I move the picture all the way to the left in 521 mode there
is something on the screen but it's all crooked
I can think of two possibilities: B sweep delay is not reset to zero in 5/2/1n mode (there is a circuit to do that), or there is a little circuit that shifts the screen left in B sweep mode (Q1331 in <11>) that is not working.

Delay not set to zero:
In 5/2/1n mode B timebase is used but delay is set to zero. It could be that the delay is applied still because of some issue. On <7> switch A9 opens in 5/2/1n mode to set time delay zero independent of delay knob. It is possible the delay pot is dirty and not making a good contact. What voltages do you see at pin 3 of U910 and base of Q902B in 5/2/1n mode?

B sweep shift:
B18, B22, B1-4, control left shift of trace in B sweep. You can check B18 and B22 by measuring voltages at J3 and J5 on sheet <11>

I looked at A sweep, A gate, and B gate signals on my 485. A sweep and A gate signals stay same as 10ns setting when you are in 5/2/1n. When in A sweep B gate is not there until you hit 5/2/1n, then B gate starts at the same time as A gate (zero delay).

I remember you didn’t see A gate in 5/2/1n. Could you re-measure again between 10ns and 5ns settings? May be "B ends A" is active although 5/2/1n should turn it off. On front panel you will see “B ends A” next to the hold-off knob. Does it make any difference if it is not in “B ends A”? If it does A2 switch on <9> is dirty.

B sweep in the positions 10us to 0.2us is showing it 10x wrong
I read as B sweep runs slower.

So 100ns is shown as 1us
Is 0.1us also 10x slower? Above statement was for 10us to 0.2us.

How is 2ms, is it also 10x slower?

You may want to check relay K1241, caps C1443, C1442.

Switch B18 turns on a 2x multiplier, if it is not working you will get 2x slower.

Ozan


Re: How to troubleshoot a faulty 7B92A?

Thierry Delaitre
 

thanks both

I've tried putting the 7B92A into the left vertical slot

I can see a horizontal line which I can move up and down using the position button of the 7B92A

There is no sweep coming up. the line remains horizontal

Thanks

Thierry


Re: 485 super weak brightness control

Tom Lee
 

I agree, Ondrej. Although other things could be at fault in the abstract, an exact factor of 10 is much more likely to be due to a switching-related problem.

-- 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 3/19/2021 13:02, Ondrej Pavelka wrote:
Hi Mark,

It quite possible the behaviour at the higher frequencies with the picture
hiding to the side could be leaky transistors but the fact the time is
exactly 10x wrong looks more like some relay ot bad contact.

On Fri, 19 Mar 2021, 17:22 Mark Vincent, <orangeglowaudio@gmail.com> wrote:

Ondrej,

Note where the pots R863, R1226 and R1228 are and turn them back and
forth. One or more may have a open due to not ever being moved and turning
it restores contact. Check for B+ at places that got to a supply voltage,
e.g. H3 and H4. Some other contacts short/go to to ground, e.g. G1 on <7>.
See if those are going to ground. The relay mentioned earlier could have
dirty contacts in it. Another part that can give problems are 151-0367-00
(selected from 3571TP). These usually are leaky from C to E. Later ones
that have a blue face are alright. Black face ones are very likely leaky. I
have replaced them in scopes and 7B time bases with KSB10U. The pinout is
different for these, BEC. The leakage was a problem, for me, at the higher
sweep speeds and was right after I replaced the transistors.

Mark







Re: 485 super weak brightness control

Ondrej Pavelka
 

Hi Mark,

It quite possible the behaviour at the higher frequencies with the picture
hiding to the side could be leaky transistors but the fact the time is
exactly 10x wrong looks more like some relay ot bad contact.

On Fri, 19 Mar 2021, 17:22 Mark Vincent, <orangeglowaudio@gmail.com> wrote:

Ondrej,

Note where the pots R863, R1226 and R1228 are and turn them back and
forth. One or more may have a open due to not ever being moved and turning
it restores contact. Check for B+ at places that got to a supply voltage,
e.g. H3 and H4. Some other contacts short/go to to ground, e.g. G1 on <7>.
See if those are going to ground. The relay mentioned earlier could have
dirty contacts in it. Another part that can give problems are 151-0367-00
(selected from 3571TP). These usually are leaky from C to E. Later ones
that have a blue face are alright. Black face ones are very likely leaky. I
have replaced them in scopes and 7B time bases with KSB10U. The pinout is
different for these, BEC. The leakage was a problem, for me, at the higher
sweep speeds and was right after I replaced the transistors.

Mark






Re: Changing out GR874 connectors +Printact relays

snapdiode
 

The 1A5 uses a Printact. At least mine does.


Re: TM500 Tester Board Sets Delivered!

Dave Seiter
 

Larry,
Thank you once again for your effort!  
-Dave

On Friday, March 19, 2021, 12:20:01 PM PDT, Larry McDavid <lmcdavid@lmceng.com> wrote:

The final shipment of TM500 tester circuit board sets was delivered to
UK a few days ago. Tracking showed one delivery to Spain still pending
but upon inquiry it turns out that package was delivered more than two
weeks ago but Spain did not update the tracking data.

So, that completes the TekScopes and Tek500 group purchase of these
circuit boards. I have residual boards for all but the main circuit
board. Jared Cabot is working to set up an independent order record at
PCBWay so that interested individuals can order the main board; PCBWay
will have a minimum order of five boards and we don't yet know the price
for such a small quantity of those circuit boards. I'll report that when
I hear from Jared or he may announce it himself here.

Well, it has been an experience! I did not anticipate such a large
response when I innocently inquired here if anyone was interested in a
group purchase of boards! And, we have learned that international
shipment delays are unpredictable now.

I wish all the tester builders well and remind you that support
information will come from Jared Cabot. I am just a messenger!

--
Best wishes,

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


TM500 Tester Board Sets Delivered!

Larry McDavid
 

The final shipment of TM500 tester circuit board sets was delivered to UK a few days ago. Tracking showed one delivery to Spain still pending but upon inquiry it turns out that package was delivered more than two weeks ago but Spain did not update the tracking data.

So, that completes the TekScopes and Tek500 group purchase of these circuit boards. I have residual boards for all but the main circuit board. Jared Cabot is working to set up an independent order record at PCBWay so that interested individuals can order the main board; PCBWay will have a minimum order of five boards and we don't yet know the price for such a small quantity of those circuit boards. I'll report that when I hear from Jared or he may announce it himself here.

Well, it has been an experience! I did not anticipate such a large response when I innocently inquired here if anyone was interested in a group purchase of boards! And, we have learned that international shipment delays are unpredictable now.

I wish all the tester builders well and remind you that support information will come from Jared Cabot. I am just a messenger!

--
Best wishes,

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


Re: 7D15 internal trigger not working

Mark Vincent
 

Steve,

Check the 151-0402-00 transistors. These are the same number as the 151-0367-00 3571TP. These are likely leaky. I had a triggering problem with mine and these transistors were bad from C to E. These check as a diode that way. I put in KSP10BU as replacements. You should see the leakage in-circuit. A VTVM or VOM on R X1 will have about mid-scale deflection on the leaky ones.

Check the ESR of C27, C40, C127 and C140. If high, replace them. Mine were high and were replaced with film types. See if any other of the 1mfd axial condensers are high in ESR and replace those that are high.

Mark


TDS 684 Scope

Thomas Dodge
 

Hi,
I have several Tektronix scopes. My newest one is a TDS 684A, and I have posted about it before. I found it in a surplus place, and I had been wanting to pick it up for a long time. When I brought it home, and powered it on, all the panel lights came on, but didn't do anything else. I powered it on and off a few times, and it started to work, ran the self test, and everything was cool. I kept it on for a while, and then turned it off. So it is a little tempermental. I am trying to find out if there is anyone in the San Gabriel valley area near Pasadena, who I can work with to fix this scope. It is in excellent condition, and is the best scope I have out the three scopes I have. If anyone can let me know if they know someone in this group, that would be great. Thanks.
Thomas Dodge


Re: Replacing a 7000 MF Rear Interface Connector: IS THIS EVEN POSSIBLE?

Clark Foley
 

After 45 year, I can still her that sound again. No. This is not a translation of Bizet’s Les pêcheurs de perles.
That distinctive crunch was an immediate indictment to all the someone has abused the poor mainframe. If you were lucky, it was a couple if pins accessible from the left or right side of the instrument. There were a couple people on the manufacturing line who were very good at reworking those connectors but you got a scolding first. One “bad dog” lecture taught me the lesson!
If you have a donor, use it. If you are daring (dashing won’t help this time), have infinite patience, a steady hand and some clever fixturing for alignment, you might get most of the pins restored. My experience from long ago was that there was always a pin that looked ok but should have been replaced.
Use the donor and use your spare time to listen to some Bizet.


Re: 7L5 dot frequency reset bug - any clues or a fix?

Richard Steedman
 

Dan, did you ever get round to trying your proposed fix of increasing the C841/R841 time constant? I can confirm that the 7934 mainframe also has the issue. See two photos here of the >1s delay after power-on before TS1 pulses appear. I suspect the issue affects any mainframe using a readout system newer than the original analog ROM board (e.g. microprocessor for the 7854 and EPROM-based board for 79xx). I suppose these days one could also whip up a fix using a PIC to drive TS1 pulses into the serial clock input shortly after power-on and then get out the way to allow option circuitry to take over.


Re: Changing out GR874 connectors +Printact relays

Ed Breya
 

The 576 uses some Printact relays. Ed


Re: 485 super weak brightness control

Mark Vincent
 

Ondrej,

Note where the pots R863, R1226 and R1228 are and turn them back and forth. One or more may have a open due to not ever being moved and turning it restores contact. Check for B+ at places that got to a supply voltage, e.g. H3 and H4. Some other contacts short/go to to ground, e.g. G1 on <7>. See if those are going to ground. The relay mentioned earlier could have dirty contacts in it. Another part that can give problems are 151-0367-00 (selected from 3571TP). These usually are leaky from C to E. Later ones that have a blue face are alright. Black face ones are very likely leaky. I have replaced them in scopes and 7B time bases with KSB10U. The pinout is different for these, BEC. The leakage was a problem, for me, at the higher sweep speeds and was right after I replaced the transistors.

Mark


Re: Q122/222 Jfet J300 subs for 2215A scope ?

charlesterrebonne@...
 

We will have closure to this thread/story now:

I ordered 25 x J300 (NOS?) from BGMicro after previous poster pointed out they had some...hoping these were real/NOS...because no photos of markings on part...ok lets try...if these are real NOS a few J300s can be nice to have around...because this was now just a matter of getting an answer to this story...I have several more recent oscilloscopes...

Parts arrived this morning. Im not fake a semiconductors expert but I have bought & seen a lot (too many) fake semiconductors in last years. The J300s from BGMicro looked ok to me.

I Installed a random J300 jfet from the 25 in ordered (tested quickly with PIC based component tester... didnt test IDSS) in Q222 position (B Channel) of the 2215 Tektronix scope that I had tried so many other jFETs in there to sub a J300 Jfet (read thread for whole story)...and...Works!

Looks like : These scopes were built with J300s Jfets there. Thats what was in the orig working channel. Thats what works. This scope looks like it was a repair attempt of a defective channel with a J210 Jfet (tried several other # Jfets) that doesnt sub for a J300 in that circuit.

Thanks to all who commented and contributed and extra thanks to SCMenasian who pointed me to BGMicro for some J300s...with a coupon code...that worked

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