Hello Specialists,

Maybe you could give me some advice how to "debug" my broken TEK 475.

It had worked the hour before and I switched it off.
Realized that I might need it later, I repowered it again, but the Fan started and stopped immediately and the graticule lighting was off. No trace.

I have the ARTEK manuals and the Repair manuals of the US Military. (I have not opened the scope yet).
I concluded that at least the +15V Power Supply has failed but I understand (from the SM manual P172/240), that there is a "hierachy" of power supplies and that, if a PS "higher" in the hierarchy fails, it will influence the lower ones.
Apparently to protect circuits from unbalanced voltages. (is this correct?).

Questions;
1) I understand that I should start with checking the +50V (UNREG) and then 50V (REG)\, next the+ 110V, +15V, and then +5V, -8V and finally -15V.

Is this correct?.

3) Are the composed PS Buffer electrolytic capacitors still available as New Old Stock?
4) I understand that TEK used a way too low margin in Voltage rating for the Tantum capacitors on power rails.
- Are there any which particularly have a bad reputation and should ALWAYS be replaced?.
or
5) Should I eventually replace ALL those tantalum caps on the various power rails with 105 deg. C electrolytic capacitors?
- or are there "solid aluminum" alternatives to the tantalums used in that era (mid 1970's - mid 1980 's ?

Appreciate your advice, before I will be embarking on a repair attempt.

NB.
I have a HAMEG HM-605 (60 MHz) which I had to repair (broken Bridge rectifier (1 diode interrupted) in a -12V supply rail) , before I could trying to repair the TEK.
The HAMEG suits me well, but the TEK 475 has a much higher bandwidth (200 MHz).

So I like to resurrect the TEK 475.

On 2021-10-17 11:12 p.m., toby@... wrote:

Hi,

Was testing my Tek 606 yesterday, and after power on and the next few
minutes it made about five "snap" discharge sounds with fluctuations
in brightness. After the last one, I lost trace permanently.

Checked LV rails and all are spot on except for the +30 and +120
unregulated, which are off the HV transformer secondary. Before I go
any farther, does anyone have a good idea of what the discharges
might mean? At the moment I would plan to check the rectifiers CR756,
CR760 on those secondary taps and their smoothing capacitors C756,
C758 and C760.

Hoping the transformer itself isn't toast...

I eventually realised that my HV board is modified from the manual.
There is a manual update page at the back of the manual that describes
a similar change to the Z amplifier board, but not the cluster of
components on the HV board that look like a similar rail splitting
circuit. I wonder if there is a later HV board change? My SN is B0116xx.


Pics: https://imgur.com/a/njNQwj4

-- I've included the manual change even though it's for a different
board, just to illustrate the similarity to the circled change in the
HV board ...  even down to the 1µF tantalum(?)
-- I've overlaid the schematic plan on the actual board to show the
substantial changes, not limited to the circled area, that are not in
my SM.


I'm still hoping that the two low rails do not involve the
transformer. The transistor pictured seems to be open circuit.

If anyone reads this who's worked on a 606, any hints might be good. I
can probably just go ahead and replace the transistor although the
markings are not very googleable (and not in Tek Xref that I can see).

Markings appear to be:
  F01
  9000
  740


--Toby

Thanks for any hints.

--Toby

Nobody figured this out yet?

It was just a dirty explosion shield. The shield was stuck to the CRT glass and I originally thought that it was the CRT.