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Has anyone built a tester that would provide all the normal power to a 7000-series plug-in? Would it be worth doing? Maybe a way to do a quick "smoke" test of plug-in not known to be good. Outside of the mainframe, you'd have access to the power rails and test points.

is it worth it as opposed to putting the plug-in into a known good mainframe?

Hi Max,

That must be a relief!
I think the protective function of Q32 is needed immediately after switching the scope to on, when the power supply lines come up (perhaps one after the other). Just a guess, the manual indeed pays no attention to Q32.

Albert

Hi Albert,

Found the culprit.

The function of Q32 is not explained in the manual. Since you pointed toward Q32 and its "strange" function, just for curiosity I pulled it out.
Result: the pulse output is up and stable with positive supply in the range 13.5 - 15.5 V..
So I returned to the pcb. Q32 has a fixed bias established by R34 ((22k) and R35 (9.1k).
Measuring the two resistors, they give me 19k and 11 k respectively. So the bias point is so altered that with +15 V of positive supply Q32 is almost conducting.
Warming up, Q32 starts to conduct and pulls down the "E" signal...

I think the function of Q32 was to some kind of protection against excessive positive voltages. No other explanations are possible.

Max

I now have all the latest 4041 System Controller and 4041 DDU service manuals scans available.

Photos of the front page of all three manuals are in the forum photos - just search for 4041 to find my forum photo album.

Send me a PM if you are interested in either of these manuals.

On Sun, Jun 28, 2020 at 11:22 PM, <Maxsimmonds1337@...> wrote:

So, I guess I had better start replacing some caps, the rifa ones looked
cracked, so I'll start with these. The PSU filtering caps, are they all on
A18?

Did you find the 0.01uF X2 mains filter cap hidden underneath the mains input socket (on the main PCB)? You have to remove the socket to see it clearly and to replace the cap.

Regards,
John

Hi Albert,
thanks for your new photo.
I've added other two photos, which shows clearly that the signal at pin "E" it deads at +15V, and so the TD was killed also.
Measuring the signal on two bases of Q86 and Q88, they are just like you said, with a swing of 1 V approx between ON and OFF state, with same voltage levels you indicated.
I strongly suspect that some carbon resistor are out of tolerances, but it's almost impossible to measure them precisely without pulling them off from the pcb.
Q32 is a strong suspect. I don't have investigated its operation, I will do as soon as possible.

Max

I got a few more requests for additional scope calibration items for Tek, so added them today, along with an unusual 4 channel analog/digital Tek 2216. I bet you haven't seen one of THOSE before...
I think I have another 7K frame standardizer too if anybody needs one.

you can see everything at the stuff day page here:


I have a working Tek 2230 and 2430 still to add, and a 2465, all going very cheaply, just takes a while to shoot everything and post it. It was so much easier to just lay it out on shelves for stuff day in the past...

also added a new category on the page, LED stuff, some amazing things in there, left over from my avionics panel design days. should be useful to somebody.

all the best,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.

Hi Christian,

Rollyn is absolutely right about the 2N3055. The original hometaxial process was switched to an epitaxial process. Unfortunately the side effects of this change were not considered important enough to include in the data sheets.
The most significant changes were the increase in Ft - the transition frequency - from 0.8MHz to 2.5MHz and greater risk from secondary breakdown.
I found this out the hard way when a 2N3055 (they were all hometaxial) used in one channel of the Dynaco Stereo 120 Amplifier I built from a kit in 1968 failed. It failed in the mid-1970s and by then the 2N3055s were epitaxial. A few months after I replaced it I noticed the high frequency hiss (noise from the input transistors in the Dynaco PAT-4 preamp) was gone in that channel. At first I thought this was an improvement. When I investigated further the hiss was still there at the output of the power amplifier on both channels. I didn't hear it because the tweeter was blown out. I got the tweeter repaired and a few weeks later the tweeter blew out again.
The gain of the hometaxial 2N3055s began rolling off around 10KHz which was fine for audio amplifiers. Because the Ft of the epitaxial 2N3055 was 3X greater the small inductor Dynaco used at the output of their Stereo 120 to prevent oscillations was no longer sufficient. That was what blew out my tweeters. I only found this out years later.

There is still one more thing and this may be something you need to be aware of: The Wikipedia article on the 2N3055 at

warns against erroneous readings you may get with a multi-meter when checking the gain of the epitaxial versions of the 2N3055. It says: "[Beta] may be 100 to 200 when testing using a multimeter."

Dennis Tillman W7pF

Looking for a Tek SC-501 scope part of the TM-500 system
Thank you
Jose Orgnero

Tom: Just for reference, you might show that I do have a copy of the Tektronix TS-4353/U Distortion Analyzer manual.
I sold a dozen or so of these sets many years ago while owner of DiLette Sales/DiLette.com
I ran that company on my free time from my job as a Boeing 747 Captain for American Airlines (40+ years).
I am now retired in Florida, and no longer active in the technical electronics market.
However, I am somewhat knowledgeable about the TM-504A, which does not seem to be widely understood.
The TM-504A mainframe is quite different from the standard TM-504.
The TS-4353/U was produced for the military to house the AA501/SG505/WQ and SG-505WR plug-ins.
The 100+ page civilian version TS-4353/U manual explains it's functions quite well.
The backplane of the TM-504A was wired specifically to allow crosstalk between these three plug-ins.
I had one customer that modified a standard TM-504, but he continued to have problems to the extent that he later ended up buying a TM-504A case which eliminated his problems. So, my guess is that it was a complicated conversion.
In any event, I have a ton of old Tek hardware and manuals. At 78, I'm not inclined to spend my future scanning docs, but might be willing to help with specific requests.
Capt. R. A. "Dick" Wilson, retired.

Hi Max,

For comparison I added a photo of the waveform at timing pin E to your album.
Because of both the "+15V" effect and the temperature effect also Q32 might be suspect. As far as I can see Q32 serves only for protection and normally should never conduct. In my unit the base of Q32 is around -4 V with some spikes op to -3.5 V while the emitter is -3 V. When the "+15V" increases the base voltage will also become less negative. When Q32 conducts for some reason timing then pin E is pulled down, causing zeroing the pulse output.

Albert

It's been fifty years so I don't remember what current setting we used on the 575 to check the Hfe of the 0140's. This had to do with the HV osc in the 611 during B Phase in Plant 2 and Building 50.

My experience with the 7603 is limited to one cranky unit (out of a half dozen here) that I repaired.

I still have my stash of graded 0140's from 1970 and I found that low Beta examples in the 7603 cause a HV failure to start and high Beta examples caused it to take on a life of it's own and do silly things.

RP

Hi Max,

The waveform at the point "E" is very critical.
Blowing some compressed air in the zone around R26 / 27 / 30/37 the pulse width at pin "E"
(positive pulse at right of waveform 10) changes noticeably, influencing the width of TD pulse.
I'm reaaaaally puzzled.

At the more negative level Pin E resets the output to true zero in periods 3-6 and 9, by switching the pair Q86/Q88 such that Q86 conducts and Q88 is off. Pin E is the only Timer board output which can force zero output. We saw already that zeroing also occurs at high "+15V". Now zeroing also seems to occur before the official end of the output pulse in period 8 because of temperature effects, likely also via the observed changes at Pin E.
How locally concentrated is your pressed air? The Control board (with the comparator pairs) is probably not much affected, so the cause of your problem might well be in the Timing board. I'd still like to see the base voltages of Q86/Q88 to confirm things.

Albert

I peaked into this HV circuit and its push-pull oscillator. It seems quite simple, primitive,
It appears that before the negative HV appears there is plenty of current to the bases of the two transistors 2N3055 to motivate them to start oscillating.
If HV does not appear, it looks like Q1214 would be saturated, and the two transistors 2N3055 would be conducting plenty and getting hot.
If this is the case, something could be shorting the secondary of the transformer in its load of rectifiers/filters.

It seems strange that the beta of the 2N3055 is so critical. Why would a high value hurt the operation?
And if it is too low, lowering R1214 would inject more base current. A design issue?

Ernesto

On Sat, Jul 4, 2020 at 07:10 PM, unclebanjoman wrote:

Just discovered that R27 on the schematic is 510 ohm: on the board there a 2.0
kohm is mounted instead.
My timing board has the code number 670-1320-02 so I don't have the latest
schematic.

The timing board A1 rolled to revision -01 at s/n B080000,
then to revision -02 at s/n B091450.

R12 changed from 4.3K to 3K at s/n B091450.
R26 changed from 15K to 13K at s/n B080000.
R27 changed from 510 Ohm to 2K at s/n B080000.

On the trigger board, the snap-off diode CR66 changed
to Tek p/n 152-0252-01 (GHZ Devices, Inc. p/n GC-2534-15)
at s/n B080000. C65/R64 probably had to change at the same
time to compensate for different diode characteristics.


dan

Thanks Rollyn for the trick. Will check that. As for your beta range, I suppose it is meant at its specific operation current within the 7603?

Christian

Just discovered that R27 on the schematic is 510 ohm: on the board there a 2.0 kohm is mounted instead.
My timing board has the code number 670-1320-02 so I don't have the latest schematic. I bought mine from Dave's Artekmedia and it references the 670-1320-00 version of the pcb with only two schematic changes/additions (R60 and CR10).
Moreover: the voltages -2.5V and -3V, they vary if the + 15V varies, changing the operating point of BJTs. The -5.1 V is rock- steady.
The waveform at the point "E" is very critical.
Blowing some compressed air in the zone around R26 / 27 / 30/37 the pulse width at pin "E" (positive pulse at right of waveform 10) changes noticeably, influencing the width of TD pulse.
I'm reaaaaally puzzled.

Max

Probably to decrease parasitic inductance on the power and ground pins.? Wirebonds make great inductors, and as the edge speeds increased, ground and power bounce became a problem.? V = L*di/dt.? I assume the power and ground pins went to the center of the package.? Corner pins are the worst possible choice for inductance.Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone

74L series of chips should be checked for pin compatibility with anything else.? Not sure why they did that, but that's been a design problem for any number of years when substituting.

Also, not all 7400 series chips have power and ground at 14/7 or 16/8.? Surprise....

Harvey

That is true for other 74 series.? Should always check pinout.? Example, 74L,LS,W: 95, 85, 78, 72, 74 and maybe others.
Carl Hallberg (W9CJH)