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On Fri, Apr 29, 2022 at 03:11 PM, Jim Adney wrote:

But did you measure the ripple? It's EASY to do with your DVM: Just switch to
ACV

So, check the voltage with the DVM set to DCV, then switch to ACV and you've
got the ripple.

Your DVM probably won't give good ripple measurements if this is a switching
PS, but if it's running off anything from 25-400 Hz, the numbers will be
useful.

I tried to do that but I couldn't get anything that made any sense. Currently I am getting almost just a dot in Ext Horiz mode, when I set B Source to EXT. So now I can get a very usable X-Y plot that has just a little bit of faint noise at the far ends of the sweep but it's 95% of the way there now - it's in focus and looks pretty good. It's light years better than it was! Curiously, it is when I use INT on the B source switch is when it looks out of focus, and I have the dot with an 1/8" line extending both directions with no input. So it would seem that the noise is coming from maybe the Trigger Preamp or maybe Channel 1 vertical section? I will revisit those two areas when I get a chance and see what I can find.

Talking about PS503

mine is working BUT one of the pots is mechanically broken. I tried to repair, in vain. Couldn't find a replacement neither.
See here: /g/TekScopes/album?id=261839

If there is someone willing to part one of these I would be very happy!

cheers
Martin

David,
Adding resisters in to the collector path on a 576 will disturb the measurement and will cause the unit to be all over the map. The way the knobs are set up there is a range of resisters the can be use as current limiting resistors in the collector supply. These are NOT all available on ALL ranges. I have made a similar mistake in trying to measure the current through a tunnel diode and I put an Amp meter in the with the C->E supply with the TD. Well it turns out this was a horrible idea and it totally skewed the measurement. I was lucky I did not take out the TD because it was a D180 for a 284. $250.00 diode. The R of the meter dominated the measurement but when the TD starts switching it made the trace go wild on the 576.

This is why I mentioned qualitative vs quantitative measurements. You can easily do wave form comparisons with this method however the measured data is meaningless. Especially when changing scales. The 576 at its lowest end has a 2nA/div range. This means full scale you are measuring 20na. Any resistance and parasitic capacitance will show up and mess with the measurement.

The 576 had a catalog price in 1990 of $18,040 and many were sold at that price. This unit can out perform most of the units out there today under the $40,000 Price point. A modern equivalent of the 576 Starts at $40,000 and goes well in to the $100,000 range. I am referencing here a Keithley 4200A-SCS Parameter Analyzer. This unit uses a computer and 4 SMU units to do the analysis.

One of my wishes to preserve these instruments there is nothing on the market today that can be had for a reasonable sum especially if you need the upper voltage ranges.

Zen

I just had a look at one of mine. The incandescents are easy to replace: the connector lead is socketed, and you can wiggle the lamp out with a pair of forceps. I have definitely done this.

I blew two of these to smithereens some years ago, as I did not then appreciate that they are still on when off as long as they are powered up, even with the front panel switch off: in this mode they are just voltage-limiting to zero instead of to whatever the set voltage is. So I powered the DUT up from the mains with the PS503s still connected. Most entertaining. They had a brief altercation with the utility company, arguing abvut the voltage, which they lost. Bits of op-amps all over the room, several diodes, the current-limiting LEDs, and a few other bits and pieces.

One thing I learned then was that the current-limit display LEDs are part of the circuit, and they have a specific Vf which is important to correct calibration of the current limit pots. So you need to get the right parts, which I did from QService. Got them both back working in the end: it wasn't too difficult really.

EJP

About the non-recognition of hi/lo power slot I had a module with the same fault. Turned out it was the switch itself. It was desperately in need of cycling and eventually cleaning...

cheers
Martin

It all depends on the particular connector's state. The "adding mechanical support" approach will only work if the contacts are in place and not bent, and the covers are just not "springy" enough anymore to stay in place but are not entirely crumbling - the external supports only cover the part of the side covers that remain exposed when the plug-in is seated, i.e. they mainly just hold the covers in place.

The transplant approach which I have documented on ("obscure"?) TekWiki was necessary in an extender that I had and in an early instrument (a 7503), where a number of contact fingers were beyond salvage, and some of the covers were cracked too much to create contact pressure even if held in place. It's a lot of work and the modern connector has much higher friction and insertion force (not designed for frequent insertions I guess), but it does conclusively fix contact problems. The contacts de-solder very easily and without danger to the multi-layer PCB, because the holes are relatively wide (I suspect they were slightly oversized by design to help assembly). You may be able to salvage covers and contacts to fix one of the remaining sockets like in my case where both V slots needed replacement but I was able to fix the H slot.

BTW, at least once the contact fingers are off, you won't feel sorry about cutting up the remaining connector skeleton to hold the new connector.

Great Job!!!

Take gold star for the forehead out of petty cash.

Ross

David,

What kind of sample rate did you use for the plots?

All I have for comparison is a 7CT1N, but it's "sweep rate" is pretty slow: if you try to display more than a few curves in a family you can see the sweep with the naked eye. It really helps to have a storage scope.

It should be able to be accurately reproduced with a pretty slow ADC: maybe as low as a couple kSps; maybe 20 kSps at most? You should be able to get a good reproduction using stereo audio input to any computer.

-- Jeff Dutky

Hi,

Has anyone here repaired a failure in the 50 ohm termination on a TDS3054B (or TDS3000B series)?
I have a fairly nice unit in which CH 2 does not turn on the 50 ohm terminator.
I'm assuming the resistor is shot, but could be the relay also. I do hear the relay clicking but the actual contacts could be bad.

Thanks for any advice.
--Victor

I took a look at my notes for the non-A version from long ago (repaired a batch of these rescued from ewaste), and there's nothing in there about dificulties with lamp access, so just go slow.

I routinely replace incandescents with LEDs whenever I have to open 'em up for service. Here I used T-1s and changed R48 and R148 to around 15k-18k from 1.2k. A 1/4W rating is fine. I did not change R55 or R155, so the max LED current is a little on the high side, but that hasn't caused any problems.

These are nice little power supplies. The voltage-dependent glow is a more useful feature than I'd initially expected.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

How about an interface from 576 ( I have one ) and Raspberry Pi?

gwerl,

Check VR24 and VR30. If either or both are bad, use BZX85B9V1 as the replacement. The previous owner could have set the internal adjustments to what he wanted as the maximum. Readjust to see if that cures the output voltage problem.

Mark

This is my point exactly about feature creep on these threads, haha

Guys, it really shouldn't be that hard. As a little proof of concept yesterday (the post hadn't been approved yet and I was itchy to find a solution) I rigged up the worlds simplest curve digitiser with a super basic transistor curve tracer I got at an estate sale a while back (my 576 still hasn't arrived).

Literally all I did was add a 1 ohm sense resistor to the emitter connection and then probed across that for current and the collector for voltage into a DSO. Saved as CSV and opened as a graph without issue, looked exactly like the trace on the screen at the time and included scale. Tried the same thing with a current probe instead of a sense resistor, result looked just as good. You can take these basic ideas and optimise them a thousand ways from there, but to be honest the results were good enough that I didn't see much point digging any deeper because I had clean curves saved for later recall, which was the goal.

Based on that I ordered one of those little ICP12 boards I'd heard about on here, if it produces reasonable results I'll just stick one in each text fixture I make with a few resistors to scale voltage etc and the problem should be solved.

I just acquired a PS503a module, very clean. Upon first powerup there are two items. First. the CM7220 incandescent lamp in the positive side appears to be burnt out, resistance checks show about 62 ohms on the negative (good) lamp and over 10K on the positive lamp. Looks like a bear to get at to replace, essentially tearing down most of the front panel. Any words of wisdom here or just be slow and careful.
Second, both the positive and negative side adjust only to +/- 15 volts at full cw rotation. The dual tracking control operates properly as described in the manual. The module recognizes being in a high or low power slot, however the operation is the same. I am wondering if a prior owner may have been working in OpAmps and internally adjusted R45/145 down so as not to inadvertently exceed max supply voltage for these parts. Or there might be a common problem in the reference supply, I have not yet checked any board level voltages. Anyone have any thoughts? I do have an extender cable, to work on the module.
Thanks,
gwerl

After I successfully completed CAL 01-04, I still get a failure on boot-up. This is what it said on the scope:
ALL 00 PASS XX<F77F>

So it passes everything but fails. Huh? I found in the service manual that this happens from a Cycle Error that must be cleared by running Exerciser 03 diagnostic routine (Page 6-16,17 in the service manual). After running that routine the error cleared! Woo Hoo! My 2465 is fixed! Thanks to everyone in this forum who patiently answered my questions and offered suggestions.

On Sat, Apr 30, 2022 at 11:21 PM, si_emi_01 wrote:

Do you have a lot of Overshoot or Undershoot on the waveforms you are
supplying it? On the other scope, what is the Rise and Fall Time? If it is too
fast, since the Impedance is High, it could cause reflections. It says the
Rise/Fall time is less than 10ns.

You are likely been bit by a Signal Integrity issue. The Signal Generator edge
is too fast. With an edge as fast as that is, it needs to be terminated into
the cable Impedance. This isn't possible in your case because the Oscilloscope
Calibration routine expects certain values to be met.

As a test you could use a 50 Ohm in-line Terminator, connect that to the
Oscilloscope Input. Set the Generator for twice the Voltage level (only below
2V to protect your load and Generator), start the test and see if the problem
goes away (as a test only). If it works it is likely caused by Undershoot or
Undershoot. If not, the problem might be somewhere else in the Signal Chain.

I have no overshoot when terminated at 50 Ohms and just a little when at 1 MOhm. So I did the whole vertical calibration using a 50 Ohm terminator plug and then just doubled the voltages from the waveform generator. That worked, although I had to tweak a couple of the voltages to eliminate the dreaded limit error. So I completed the calibration. But more on this below.

On Tue, Apr 26, 2022 at 05:39 PM, <lylejlarson@...> wrote:

1) The board layout is a nightmare. Component placement is scattered, and 90%
of the reference designators are missing in the silkscreen. So locating part
positions
is so slow and tedious, that by the time I locat the part, I've forgotten why
I was looking for it.

The cross reference table listed on 4 pages before the Schematic 9 are for this purpose.
It is pretty easy to locate components on the board and on the schematic this way.
I found the scanning quality for Tek 2467 service manual better for this purpose.
See

2) It's a complex board, conceptually. Easily one of the most challenging that
I've dealt with.

No disagreement here! I am trying to understand it and I hope I am getting getting closer.

Luca

How does current that initially charges C1025 flow? Is it like the following?

T1020 PIN4 -- R1020 -- C1025 -- CR1035 -- R1046 -- T1020 PIN6

This is not the only path, but seems the least resistant one. There is also a path through CR1072 and C1072, but that path will only allow C1025 to be charged to about 10V, because C1072 is about 30 times smaller than C1025.

Luca

On 2022-05-02 5:05 p.m., lpb612 wrote:

Thank you so much Mark.
I have replaced a few capacitors that I can tell or measure to be bad. I have not gone systematically, because of the limited supply. I have order a bunch of more generic ones to replace some other capacitors as needed. I am also ordering a desoldering gun. Without it, it is very hard to put the new capacitor back on, because of the remaining solder.

If your ordinary iron is hot enough to melt it, you can remove just about 100% of the existing solder with desoldering wick.

--Toby

Thanks again - Luca

Thank you so much Mark.

I have replaced a few capacitors that I can tell or measure to be bad. I have not gone systematically, because of the limited supply. I have order a bunch of more generic ones to replace some other capacitors as needed. I am also ordering a desoldering gun. Without it, it is very hard to put the new capacitor back on, because of the remaining solder.

Thanks again - Luca