Re: Tek 465 no display


Albert Otten
 

That's a LOT of progress Russ!
With some more experience you might have thought already of a shorted C1549 after posts by Harvey and Fabio IIRC. One was that as good as zero output is a significant observation. The other that most tantalum caps have a series resistor so just one failing will not fully pull down the rail to zero. C1549 might be the only one *without* series resistor (I didn't check that).
That -6.4 V at the -8V rail could be due to a heavy load but more likely I think a bad big cap C1562. I would start there. Note that both sides of C1562 might show ripple w.r.t. ground when -8V is out of regulation. Try to measure the difference, so the ripple (and DC) across C1562. If OK then proceed with testing for current limiter activity as explained already in some posts.

Albert

On Fri, Jun 29, 2018 at 10:57 am, musicamex wrote:


One step closer! C1549 looked like it might have been replaced with a mylar
cap. As soon as I unsoldered one side and turned on the scope, the fan came
on! So i replaced it with a 47mf 25 v electrolytic and now had a bit of a
trace but way off vertical axis. Good call Albert!

The voltages now are112.5, 55.66, 15.1, 4.9 and -6.4

I see that the vertical axis is associated with the -8 rail and read the
troubleshooting for vertical axis anomalies but before I go further I thought
I check for advice here first.

Thanks in advance, Russ

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