Re: Again a 7854 power supply beast to be repaired...


Craig Sawyers <c.sawyers@...>
 

Oh dear - the dreaded one pin out problem. We've all done that at some point. I've got away with it
until I did it on my 577 curve tracer and took out most of the silicon. Fixing it is a "work in
progress".

Hopefully there won't be too horrendous damage.

Craog

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of unclebanjoman
Sent: 04 May 2019 17:23
To: TekScopes@groups.io
Subject: Re: [TekScopes] Again a 7854 power supply beast to be repaired...

O.K. I checked power rails and found a short on -15V, pin 7 of P82 connector (sense).
NOTE: some other people was attempted to repair this poor 7854, so...they left behind a disaster
with
no success.

After careful inspection I found the P132 connector on the motherboard mounted wrong, shifted one
pin left!
I pulled out P132 connector and reinsert it in the correct way, carefully matching all the pins.

Power up and... woah! It started! All the lights up!

BUT: now the bad surprise.
On the CRT I see a BIG unfocused and very, very brilliant spot centered on the screen (no plug-ins
are
inserted). The INTENSITY control has no effect (fully counterclockwise).
To avoid damage to the crt I turned it off immediately.
I turned the scope back on, just to perform a quick check on the low voltage regulator board A22:
all
voltages are perfect, all in range.

And now? Z board damaged? :-(
Where to check?

Max

.

Join TekScopes@groups.io to automatically receive all group messages.