Re: TDS794D, alleged shorted power supply?


Richard Knoppow
 

Do you have or have access to a metered Variac? If you do connect it and start with low voltage and watch the current meter. Be ready on the Variac power switch. Current can come up pretty fast even if there is no short but a short will generally draw a lot of current right away. I would not be too concerned with the seals since this is a "reject".  How do you know the line cord is good under load if you haven't powered it up?
   Either put it on a metered Variac or dim bulb tester or stick it in a display case.
   Of course, I would open it up first and look for any signs of something shorting. Have someone else follow you up, its easy to miss even fairly obvious things.

On 7/28/2020 2:30 PM, Roy Thistle wrote:
I've got this TDS794D in skookum cosmetic shape... that is just daring me to plug it in, and boot it up. Only... the... assumed... "dumpster diver" I got it from claims... "It has a shorted power supply." Further query directed to the dd, did not elucidate significantly.
Fuse has continuity.
Line cord is good, under load.
No toasty smell to it.
I can't see as it has ever been opened (It still has an intact SIMCO, anti-tamper/cal sticker on it... and none of the usual clues a thing has been opened, since SIMCO had it.)
I am kinda chicken to try to power it up... because, I so want it to work... or be an easy fix.
The only explanations... for the "explanation" that it has a shorted power supply...that have crossed my mind... is that that is what SIMCO reported... or documented... if the 794D was indeed sent to them for cal/repair... or even came from them... maybe from an equipment auction?
Another thing that I was thinking it that if the scope boots, at least to error checking, would it report and error indicating a shorted (low?) power supply?
Any suggestions/recommendations, on how to proceed? Any "gotchas" to watch out for?
Anyone got a screen shot of one booting?
The service manual (from the Tektronix Website) has a reasonable service flow chart... so if I dare to plug it in... and it starts to boot... I can work from there. (I don't see anything about error reporting... or explanations/table of error codes.)



--
Richard Knoppow
dickburk@...
WB6KBL

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