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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

I have uploaded the Gerber files for the PCB I designed to replace the electrolytic cans with snap-in caps in the 465B (not sure if it is compatible with the 465 but I'm thinking it probably is).

This is the link to the folder where the Gerbers are and a PDF of how to implement the PCB. Note that that pictures in the PDF are of the older board and the Gerbers are for the newer version.

If anyone spots anything amiss about this, please let me know. It's been a few years since I did this and I'm pretty sure the Gerbers are of the last, correct version.

/g/TekScopes/files/PCB%20for%20465B%20Electrolytic%20Replacement

Thanks,
Barry - N4BUQ

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.

Update: I found C962, filter capacitor for the +8.6 V supply was shorted. Once replaced (original 840 uF, 12V replacement 1000 uF 10V), the power supply makes just one chirp, and the instrument starts working...kindof. I suppose the short on the secondary was causing extra current to flow in the primary, preventing the primary oscillator from reaching 43V at which point the oscillator's duty cycle would have changed such that it would be able to power itself.
Now I have jitter in the horizontal deflection. The B sweep delay pot seems to be able to calm it down, but it comes back. Intensity, focus, position up/down and right/left work. I suppose I'll figure out how to access the front of that pot to inject deOxit and if the problem persists, then start tracing the horizontal deflection signal back to the sweep generator.
Halden VE7UTS

Looking at it again, I believe these Gerbers are from the final version so no traces have to be modified.

Barry

Jon,

Actually, I didn't realize I had this but I have a previous version of the Gerber files of it that I think can be easily modified. IIRC, one of the traces needs to be removed and I can identify that. I think that may be the only issue with it. Do you want me to send the zip file to you?

Thanks,
Barry - N4BUQ (ex WB4MXR, ex WN4MXR)

I _might_ have an earlier version that had a mistake or two on it. The basic outlay would probably be the same. I'll check and get back with you.

Barry - N4BUQ (ex WB4MXR, ex WN4MXR)

OK, Barry. Thanks for the reply.

I can fabricate my own board. Do you have a photo of it? Any information about it would be very much appreciated.

Jon -- WA0ANA

Those things are easy enough to make. I made up some designs using a paint
program and printed them on pnp blue.

There's also somebody on ebay selling them. Do a search for "Tektronix
capacitor adapter". I see a set for the 465 for $10 or best offer.

I don't know the seller, but they sold a couple hundred of them.

Paul

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Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Linux/Unix - We don't do windows