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Mark yes Nichicon are high quality caps.

My 7904 backplane had a 9 mF lytic, axial, not tant.

I think the end seals failed.

Indeed on a 50V bus, replaced with 100V axial.

Very common failure on 7xxx scopes,

Jon


Jon

I was recently in a discussion about an HP scope that suddenly developed a ghost/reflection on the CRT that followed the beam image. The pictures of the effect showed exactly the same sort of thing that I have seen on my recently acquired 485, and which I have heard about (but not observed, except at high beam intensity) on the 475. The interesting part was that the ghost image suddenly appeared during his "soak test" of the scope. Here is the description:

Help please. HP 1725a, ebay purchase.
Received with broken knobs and some badly remounted y amplifier PCB.
Dismantled and cleaned the timebase switches, reassembled with all working OK.
Left to soak test, just noticed a sudden brightening from the CRT in my peripheral
vision. Since then I have a ghost around the CRT beam. This effect is most easily
seen in x y mode.
All LV voltages are within spec with no ripple. 20V unregulated is at 23 VDC with
some ripple as to be expected. Additional capacitance added to this line has no
effect on CRT display. -3kV supply is present and correct.
Focus, astigmatism and pattern work as expected.

The accompanying images look exactly like the ghost image that I see on my 485.

After verifying that the 1725A did, in fact, use a CRT with an expansion mesh, and further investigation it was determined that the mesh bias voltage had no effect: if the mesh bias was disconnected the ghost image remained. If an external mesh voltage was applied, the ghost remained, and changing the mesh bias voltage up or down did not affect the ghost in any way. The conclusion (which may be premature) was the the expansion mesh was "open" inside the tube (I think that there's still a chance that it's disconnected outside the tube, but that has not been verified).

I had been led to believe that this ghosting was just an unavoidable feature of the expansion mesh, but this suggests that, at least in some cases, the cause may be pathological, and might be remediable. I'm planning to make a similar investigation on my 485, and will report back my findings.

-- Jeff Dutky

Steve
I have available 2ea 366-1338-00, 1ea 366-1385-01
These are not in original Tektronix packaging but we’re originally purchased as NOS parts.
If you are interested contact me offline with request.

Craig

I have a AMI S68A08P in my 2465 and it is not socketed. I'm pretty sure no one has worked on it prior to me owning it.

One thing that can affect the "E" output (pin 37) is MR (memory ready, pin 3). If MR is low, the processor will stretch E and keep it high. The MR signal comes from the buffer and option boards, but even if you don't have any options it would be good to check the logic level of MR.

-mark

Jon,

Thank you for replying to my question. For 2/, the ULD 47 mfd I use is a low ESR type to replace the 6,8-15mfd tantalums. So far the ULD types have worked well, if not better.

The 5/ looks like many of the 7000 series. The tantalums are on the 50V and some of the other supplies. The supplies, I use UHE types with a higher capacitance and voltage on the 50V supplies. The UHE is also a low ESR type. The 7000 types I have now have them on the back plane and work fine. I used 100V types on the 50V supplies. The two types are made by Nichicon in case you want to look up the series.

Mark

I made this video for a PG506 knob, but I had previously made the mold to cast a volts/div knob for a 485, since the grey part and the aluminum insert are identical:

--
Bob Haas

Steve,

If you could get a measurement of the diameter of the inner aluminum core of the VOLTS/DIV knob I can try making a casting from one of the knobs on my 485. If that goes even passably well I can send you the resulting plastic shell which you could use to mend your shattered plastic. I expect that the casting will not fit flush against the metal core, but that can be remedied with some needle files and manual effort.

I have done something similar to repair the VOLTS/DIV knobs on a 475A, but I used the remains of another knob. I've been working on my casting techniques because I would like to be able to repair such broken knobs without reducing the overall supply.

-- Jeff Dutky

Jeff-
when we we did silicone molds for wafer handling we put the assembly in a vacuum chamber to remove all bubbles/voids during cure.
might work with epoxy? seems to be about the same consistency, no way can you use the fast set epoxy though.
another possibility is put the casting on a vibrator for a while to settle the contents.
搁别苍é别

The VOLTS/DIV knobs are part number 366-1338-00. They were also only used on the 485, so again, hard to find spares lying around (but maybe not impossibly, as twice as many VOLTS/DIV knobs were produced as were TIME/DIV knobs).

Depending on how much of the plastic remains on the knob you have you may still be able to make a casting from which a patch could be constructed.

My current method uses plasticine modeling clay as the mold, and common JB Weld epoxy to make the casting. I have a lot of trouble with bubbles and narrow-walled parts, but if I had a VOLTS/DIV knob that was cracked in half I think that I could do a fair job of casting the half-shell. Once you have the plastic part you can file it down to fit in the gaps of the original knob.

-- Jeff Dutky

Whoops, I misread your request as the TIME/DIV knob. The VOLTS/DIV knobs are another matter.

-- Jeff Dutky

The knob is actually several parts: 366-1385-00 (or 366-1385-01+366-0293-01 for SN B090000-B142149) is the outer grey knob, and 354-0413-00 is the transparent skirt. So it makes a difference what the serial number of your instrument is.

Sadly, according to the RPR-knobs&pushbuttons, these were only used on the 485, which makes finding a spare one unlikely.

How much of the knob plastic remains on your knob? (not to ask an indelicate question)

It might be possible to make a mold from the existing plastic and fashion a patch from the casting. This is something that I have been experimenting with, though I have not yet struck upon a method that produces perfect results.

-- Jeff Dutky

"No, because a dimmer would work there either way round"
I'm sorry... No, what?

I wasn't actually suggesting using a light dimmer, just illustrating a soft start ;)
Also it would take a hefty one due to the high surge current for the first second when the inverter starts (around 40 amps RMS on my clamp-on).

My 485 works fine but knob plastic cracked. Anyone have a spare?

Forgot to add a 4th item:
The 0.8 Amp Circuit Breaker for the Collector supply.

Thanks,
Charlie

Thanks Keith for the info, had seen those autotransformers on ebay as well, will check them out.

311-1702-00 is the one I am actually looking for. R1070 on the Timing Board. It is the pot controlled by the red VAR knob in the middle of the A and B TIME/DIV and Delay Time control knobs.
I will definitely reach out to the VintageTEK people to see what they have.
This is by far the most complex restoration I have ever done. I have fixed up some old musical instrument amps and stereo systems, but that was limited to replacing caps and cleaning pots. This is a monster compared to those. Fortunately I have a friendly shop close by that repairs electronics and I think they can teach me how to calibrate it when I am done.

Hi Charlie,

re: rear fan filter frame. Here's one that might work.



This is from MercedesMan aka "Tubehunter". He will have a lot of 5 series Tek parts from time to time. I've bought from him before.

re: 575 auto-transformer. Just agreeing with your suspicion that the generic Powerstat 10B could work. I have a 575 and I also happened to have a couple generic 10B's that I bought off eBay. They looked identical, right down to the label, with what is in my circa 1962 575...so I tend to agree with your idea that a generic 10B will work.

Sadly, I blew up both of those powerstats several years ago in a failed experiment. But good news is that I easily found them on eBay for a very cheap price, so there is hope.

To that end, here's a couple eBay powerstats that look like mine (working from memory here, but pretty sure this is it)



and here's another



Hope this helps a little.

Looking for 3 parts for my Tek 575:
1) The Collector Supply Auto Transformer. The 576 used the same one up to s/n 326319. Its a Powerstat 10B-1218, but it looks like any Powerstat 10B would work.
2) The rear fan filter frame. The one from my 547 fits, but has the corner indentations for the power cord. So in a pinch I could use on of those.
3) Feet. My unit is a very late ('69) build, has (had) plastic feet with 2 mounting screws each.
I'm in the US, Milwaukee WI area.
Thanks,
Charlie

Mark....2/ unsure of ULD. Beware

ESR of a tant may be much lower than an equivalent size or capacity electrolytic.

5/ the backplane of 7904 had some axial caps and at least one had failed, but perhaps not a tant.

the voltage of the Tektronix cap was very close to the power bus bypassed.

Jon

I've just replaced the TekWiki PDF () with a 600dpi grayscale scan from an original chart so things like the polarity switch labelling are no longer blacked out.