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CLA pot?
check if defective and replace pot?

J

Hi, I own a TDS694C which has a similar power supply. Worked fine but after
sitting on the shelf for a long time died on the first power up.It produced
modulated high pitch sound on standby power, and died completely on
attempt to turn main power on by the front button.

The first thing I found was a dried and blown 1000uf EC in the power
supply, s main line, C124 in TDS520B schematics. After replacement nothing
good - no standby power. Measured conductivity of integrated PWM (U12)
output transistor - open in both source-drain directions, not good. It was
TOP200YAI Replaced with a newer and more powerful TOP204YAI. Still nothing,
no input voltage on standby PWM. High voltage Zeners were ok (tested with
curve tracer, you can also do that with auto transformer and rectifier on a
breadboard, but be careful with high voltage!).
Walking along the supply line I have found a non-conducting current
limiting 1W resistor, R176. It was 2.4Ohm in my PS and *fused* 27Ohm in
TDS520B. It just cracked when the integrated PWM was blown by the voltage
spikes. Very thin crack, visible under microscope only. So it is fused in
TDS520 for a reason. Replaced with a new one and the problem was solved - I
immediately got standby power and good main power after.

Best,
-Andrei

Hey everyone, I’ve got a Tek 7704a where the readout that SHOULD be at the top and bottom is offset and near the center.

Adjusting the vertical separation pot didn’t fix it, it won’t adjust enough

Any tips?

FS: Tektronix Type 1101 accessory power supply
LEMO connectors (4) on front panel.
+15VDC -15VDC +5VDC
TESTED, Works as it should.
Serial # B042132
$150 by PayPal or Zelle
Ships from Dallas, USA
Free shipping for US 48 states, other please ask for quote.
PM me off list with inquiries.

Ron

Those work well and I've used them in a couple of Tek scope power supplies. The thing I don't much like about them, at least for this application, is once you solder them in place, then if you ever had to replace the cap, it's necessary to remove the adapter which is more risk of heat damage to the circuit board. If, though, you have really nice desoldering tools then that might not be as much of a concern.

Thanks,
Barry - N4BUQ

Strange, I emailed a reply and it never showed up.

On Ebay, search for Tektronix capacitor adapter. Somebody is selling a set for the 465 for $10 or best offer. I don't know the seller but they've sold a couple hundred.

Hi George,
I just bought a Tek 2232 with GPIB option. I see that you intentionally installed this option on your 2232 a couple years ago. Maybe for transferring data to a computer? It seems the original plot options require vintage plotters. Do you know of any modern scheme to emulate such a device and generate a bitmap or jpg file of the CRT display? Or should I rig up a cellphone holder in front of the CRT for this?
Cheers
Halden

On Fri, Nov 15, 2024 at 1:04?PM rafael suarez via groups.io <rafik69pe=
[email protected]> wrote:

I’m afraid I don’t have a curve tracer. Perhaps there’s another way to
test them?

The TVSes should measure open in both directions, until you reach somewhere
beyond their threshold voltage. This is 220/250V respectively, which is why
they're challenging to test. If you can somehow provide a current limited
(1mA will do) ~300V DC, you can simply measure the voltage drop across them
in both directions. It should be roughly 250/220V respectively.
If you can't, perhaps best to leave them alone.
If they've failed open, your switching transistor will fail, though it may
take it a while. If it comes to that you'll want to change both TVSen and
the transistor. I seem to remember replacing a BU508, which is easy enough
to source.

On another note, I’ve found a few solid SMD capacitors in bad condition on
the large board visible as soon as you open the scope.

That would be the CPU board. Also look at the acquisition board, the front
panel board and whichever other boards you have in the scope. If the
electrolytic caps are the same make and vintage, the odds are that they've
failed or are going to fail.
There are many threads in this forum about how to clean boards that have
suffered electrolyte leakage. The problem is that traces may have rotted
away, and if they haven't yet, they may still rot away if the electrolyte
isn't cleaned and/or neutralized.
I believe in North America the recommendation used to be to wash thoroughly
with; Simple Green, distilled water, IPA and then leave the boards to dry,
or "bake" them at a very low temperature. Getting under components where
electrolyte may have pooled can be difficult.
There are many stories of people who managed to find and repair broken
traces and probably as many, of people who gave up. My TDS684B(? I forget)
has never yet worked, even though I cleaned it and changed the
electrolytics :/.

Good luck,
these are very capable scopes and well worth putting some time into.

Hello everyone,

Thank you for your quick responses. I will follow your suggestions as soon as I return from work. I’m afraid I don’t have a curve tracer. Perhaps there’s another way to test them?

On another note, I’ve found a few solid SMD capacitors in bad condition on the large board visible as soon as you open the scope. I’ll follow your advice and let you know what I find.

Best regards.

Hello everyone,

Thank you for your quick responses. I will follow your suggestions as soon as I return from work. I’m afraid I don’t have a curve tracer. Perhaps there’s another way to test them?

On another note, I’ve found a few solid SMD capacitors in bad condition on the large board visible as soon as you open the scope. I’ll follow your advice and let you know what I find.

Best regards.

Hey Rafael,

I second Jared's advice; you'll probably want to have another look at the
PSU. The standby supply in these scopes is notorious for giving up, leading
to dead or hiccuping supply. AFAIK there are two main versions of the
standby supply, the earlier "discrete" one and the later "integrated" one.
You'll find schematics for the "discrete" one here:
(PS).pdf (thanks
H?kan). The later version has an all-in-one switching regulator, which
you'll find in the TDS520B component service manual. This is available from
Tek (as well as from TekWiki, I believe).
The regulation loop in the "discrete" standalone supply is non-obvious (to
me) so I simulated it, and found that a high-ESR C17 wrecks it, though I
don't remember the details beyond that. ISTR that the TVS diodes VR4/VR5
and Q2 get stressed when C17 is high-ESR, so you may want to replace or
check the TVS diodes at least. If they fail open, Q2 will die after a short
while. I should note that without e.g. a curve tracer that goes to >250V,
it's not easy to test the TVS diodes, but maybe you have a suitable curve
tracer at hand - you wouldn't be the only member of this group so equipped
:).

I think you'll also want to look for leaking electrolytic SMD capacitors
elsewhere in the scope. I don't know whether the capacitor plague affects
the TDS744A in particular, but it's wrecked many otherwise good TDS scopes.

Siggi

On Thu, Nov 14, 2024 at 7:57?PM rafael suarez via groups.io <rafik69pe=
[email protected]> wrote:

Good afternoon, I am a humble electronics hobbyist with some knowledge. I
have repaired various household devices, but this time I decided to take on
repairing my TDS744A. I bought this scope online from Japan. When I first
turned it on, there was no image on the screen, though it did display
through the VGA output. A few days later, I turned it on again, and only
the front panel LEDs flickered.

I have recapped the entire CRT board following all recommendations, and I
also replaced the RIFA capacitors in the power supply. Unfortunately, the
issue persists. I don’t want to go any further on my own and am reaching
out to you for assistance. It would be very helpful if you could advise me
on where to look to resolve this issue.

I would be very grateful for any suggestions. I’m attaching a video
showing the issue. Thank you very much in advance.

I turned on my TDS380 yesterday and the CRT flashed some garbage and the front panel LEDs all came on and stayed on but that's it. I'll pull it apart this weekend and start looking for obvious failed components on the PSU and also check the capacitors for ESR and capacitance, but thought I'd check here to see if anyone has had a similar issue with their TDS3xx scope. The SM has a power troubleshooting section that has you disconnect the boards one at a time which I'll also run through . . . . Thanks in advance for any input.

Rich

7904 psu service is a nightmare. I had to do a full recap and hated it. Instead of disturbing the custom transformers, I clipped the leads and soldered to them. Still love the 7904 for it's calibrator, fanless operation and the control illumination switch on the front. Also, there's very few custom ICs, which is nice.

7904 lacks pulsed display mode if that is important to you.

It looks like the PSU is hiccuping. First up, I'd try unplugging the grey ribbon cable to the CRT board to isolate it from power to check it's not still bad somehow.

Have you replaced C17 in the PSU with a new low ESR cap? These are *always* in need of replacement, and can take out a few other parts if left alone..
Check a few other parts as per this image to make sure the standby power is ok:

There are a few known problems with old capacitors in these PSU's, and being an A model, it will be older and the capacitors nearer the end of their life... I have personally found a couple PSU's needing a complete set of replacement capacitors in older scopes.

Are you located in Japan? I have a bunch of spare parts for these scopes including working PSU's and CRT boards, so it wouldn't be difficult or expensive to figure out a trade etc.



Jared

In particular, the ability to raise the upper half of the later models onto the integrated "kickstand" in order to more easily access the controls and components in the lower half of the 'scope makes working on those much more pleasant.

I had worked on a 7904A, a 7104, a 7934 and a 7854 before tackling a then-new-to-me 7904. I was unpleasantly surprised to find that the 7904 did NOT have the "kickstand" feature. I repaired that 'scope and sold it.

DaveD

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Hi all,

I have P6042 current probe that works well but the thumb button has popped off the slide assembly. The probe is still perfectly usable by manually sliding the head open and closed. The thumb button has 2 plastic protrusions that are intended to fit into two holes in the slider assembly but when I hold it on with finger pressure the slide can't be opened fully. It seems that something has given way or snapped off the plastic. I would be grateful for any advice abut how to fix this or failing that, I'd be happy to pay for a non functioning probe head that I can use for parts. I'm in Melbourne, Australia.

73,

Morris

Barry
That's very useful - thanks!
Menahem

Barry,

I read that I should see a link to your full email address. However, I don't see one. I'd like to purchase a cap replacement board. Please email me at jonwoellhaf@....

Thanks!

Jon - WA0ANA

For the A6302 probe, you are correct, the AC signal is generated by the coil, while the DC signal is created by the hall-effect sensor. Might be a broken wire inside the probe, or possibly inside the cable, but worst case it's the hall sensor itself that's damaged. Dropping the probe could crack the sensor (silicon, i.e. a glass plate). I haven't seen any replacements available anywhere for these, and mechanically I get the impression that this would be nearly impossible to replace, even if you could find one (but I could be wrong).

Excellent!

Please send an email to <jonwoellhaf@...>, and we'll work out payment and shipping.

And -- duh -- I just noticed the link in your first post in this thread that has a plethora of photos. Great!

Jon