Re: Tektronix 2235 Oscilloscope Troubles

Jim,

If you're ever in the Chicagoland area - I owe you a cold one. I pulled the
caps from the power supply and replaced them with brand new NTE
replacements, and some NOS HV caps I had left over from a laser power supply
project. I also replaced all of the 510K 1/2W resistors near the HV output
stage since they looked like they were overheating and the epoxy coating was
flaking off.

I turned the unit on, and after a suspenseful second or two of silence, the
unit powered up, the LEDs stayed lit, and I got a trace on the screen!

I'm going to leave the unit on for a few hours to burn it in and see if it
remains stable, but it appears you hit the bull's eye on this unit. Sometime
this week, my Sencore LC75 analyzer should arrive in the mail from Florida,
and I'll be able to determine exactly which part or parts were faulty.

Thanks again!!

-Tony

"Jim Yanik" <jyanik@xxxxxxxxxx> wrote in message
news:Xns963ECB41B8899jyanikkuanet@xxxxxxxxxxxxxxxxx
> "Tony" <mrdevlin@xxxxxxxxxxxxx> wrote in
> news:f_2dnYpdHK0LTfvfRVn-rw@xxxxxxxxxxxxxxxx:
>
> > Hello, and thank you for reading my post.
> >
> > I've recently acquired a used Tek 2235 at a local auction.
> > Cosmetically, the unit looked brand new like it was hardly ever used.
> > The reason why may be that there is a slight problem with the unit,
> > possibly somewhere in the power supply section. When power is applied,
> > the unit exhibits something similar to the 12kHz "chirp" symptom, in
> > that once every second or two, the power LEDs flicker and an audible
> > chirp noise can be heard coming from the transformer.
> >
> > I've tried some basic troubleshooting steps as follows:
> >
> > - Visually inspected the circuit boards for obvious component failures
> > - Tested all diodes and capacitors of the power supply out-of-circuit
> > to make sure they were still OK
>
> did you check the PS filter caps for good ESR? Switchers (and 2200 series
> scopes)are prone to bad electrolytics WRT ESR. Don't forget the electolyti
c
> cap for the housekeeping supply for the TL594 IC. (100uf,IIRC)
>
> (I don't have 2235 schematics or manual,so I can't go into specific part
> numbers,my memory just isn't that good.;-) )
>
> You could have a problem with a HV cap breaking down,perhaps in the -2KV
> cathode supply.
>
>
> --
> Jim Yanik
> jyanik
> at
> kua.net


.

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