Re: Tektronix 532 LV rail shorted


Rajesh VS
 

Hey Randy,

Glad to know it was just the fuse. I am a bit confused about the +89V AC,
do you mean DC ?
I would ask what the the reference for this measurement - ie where is the
negative lead of the meter connected while taking this measurement.
If you suspect that some other power rail is shorted to -150, there are
many ways to confirm if there is a short, you can try measuring the
resistance from output of each rail to -150V out.
Or remove all rectifier tubes - except for the -150V rail - and also
disconnect terminal 14 from the transformer (for 100V) and then power up.
This will disconnect all rails except -150. Then you can try connecting the
rails one by one back to find out which rail is causing the short. Follow
the sequence of +100, +225 and +350 while reconnecting, as they are stacked
in that order.

All the best.
Rajesh

On Fri, Jan 17, 2020 at 7:40 AM <randolphbeebe@gmail.com> wrote:

Rajesh,

I have not had time to look at it again yet. Hopefully this weekend. One
spot of good news is that I just checked the fuse and it was blown. That
would sure account for no voltage at C640!

One thing that is curious however, upon reviewing the schematics of the LV
power supply I read my notes and recalled that when I measured the voltage
at pin 16 on the transformer it measured +89V AC. I do not expect to see
the voltage near the correct numerical value on the crippled circuit but
POSITIVE voltage? Would that account for the symptoms as well since both
C640 and C110 are installed positive to ground?

Can that positive voltage be coming from one of the other supply rails
perhaps, the +350, +225 or the +100? Or a fault in the transformer. It
gives me something to think about when I read about the circuit description.

Your time distribution method is excellent, I am trying to get away from
the neophyte's instinct to just shotgun parts to "see if it works now".

Randy



--
/Rajesh

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