Help needed with Tek 465 scope disassembly

[John]

Trying to fix my old 465 that's blowing AC main fuse on powerup. Someone
suggested checking caps on P/S, but to get to them I had to remove the
trigger generator and sweep logic board first. So far it's been
straightforward enough, mostly screws and some pin connectors.

The only things left are two BNC jacks mounted on the front panel that are
soldered to this board, but I can't figure out how to free them from the
front panel. Would hate to remove the front panel unnecessarily . Am I
missing something, or should I just desolder their connections at the board?
Thanks for your help here. --- John

 

[George R. Gonzalez]

"John" <jonnor@(nospam)comcast.net> wrote in message
news:uz43b.209609$cF.68064@rwcrnsc53...

Trying to fix my old 465 that's blowing AC main fuse on powerup. Someone
suggested checking caps on P/S, but to get to them I had to remove the
trigger generator and sweep logic board first. So far it's been
straightforward enough, mostly screws and some pin connectors.

The only things left are two BNC jacks mounted on the front panel that are
soldered to this board, but I can't figure out how to free them from the
front panel. Would hate to remove the front panel unnecessarily . Am I
missing something, or should I just desolder their connections at the
board?
Thanks for your help here. --- John

We need to backup a ways here. I've fixed many a Tek 465, and the problem
has NEVER been a shorted PS capacitor. Many an OPEN or very weak PS
capacitor, but never seen a shorted one.

You should be able to determine the problem with the power off and an
ohmmeter. Just measure across each of the capacitors. and Oh, it could be
a shorted diode bridge, those were mighty marginal, and a shorted bridge
could make a PS capacitor look shorted. You may have to unsolder a bridge
or two to isolate the problem. Which is darn near impossible as they're
often found mounted flush to the board. Since new bridges are much mor
ereliable and cheap too, one can just bend the old bridge back and forth
about 5 times and the leads will nicely break off. Then you can use a
solder-sucker to suck out the remaining wire and old solder. Then you can
measure the transformer winding and the filter cap without the questionable
bridge getting in the way.
Replace the bridge with a new 3-amp 400-v bridge to give the scope a little
headroom.


If it is one of the big PS capacitors, you can usually remove them without
removing that side board. They're unsolderable from the bottom, and you can
usually wiggle them out thru the top opening. You'll need a reasonably
hefty 50 to 100 watt soldering iron to heat up all those wide traces and
semi-massive capacitor lugs.

You'll have a bit of trouble finding an exact replacement, they don't make a
lot of those traditional FP-based caps anymore. You may have to cobble in a
newer capacitor. It's a bit of a pain, as Tek for some reason depended on
the 3 ground lugs of the FP capacitor to act as current-carrying conductors.
You may have to patch in a few jumper wires to restore continuity there.


Good Luck,


George

 

[Jim Yanik]

"John" <jonnor@(nospam)comcast.net> wrote in
news:uz43b.209609$cF.68064@rwcrnsc53:

Trying to fix my old 465 that's blowing AC main fuse on powerup.
Someone suggested checking caps on P/S, but to get to them I had to
remove the trigger generator and sweep logic board first. So far it's
been straightforward enough, mostly screws and some pin connectors.

The only things left are two BNC jacks mounted on the front panel that
are soldered to this board, but I can't figure out how to free them
from the front panel. Would hate to remove the front panel
unnecessarily . Am I missing something, or should I just desolder
their connections at the board? Thanks for your help here. --- John

I believe you can just desolder the wire to the BNCs.
I'd do it AT the BNC.Then you won't forget where the wire gets soldered.


--
Jim Yanik,NRA member
jyanik@kua.net

 

[John]

"George R. Gonzalez" <grg@umn.edu> wrote in message
news:biiumg$jiq$1@lenny.tc.umn.edu...

We need to backup a ways here. I've fixed many a Tek 465, and the problem
has NEVER been a shorted PS capacitor. Many an OPEN or very weak PS
capacitor, but never seen a shorted one.

You should be able to determine the problem with the power off and an
ohmmeter. Just measure across each of the capacitors. and Oh, it could
be
a shorted diode bridge, those were mighty marginal, and a shorted bridge
could make a PS capacitor look shorted. You may have to unsolder a bridge
or two to isolate the problem. Which is darn near impossible as they're
often found mounted flush to the board. Since new bridges are much mor
ereliable and cheap too, one can just bend the old bridge back and forth
about 5 times and the leads will nicely break off. Then you can use a
solder-sucker to suck out the remaining wire and old solder. Then you can
measure the transformer winding and the filter cap without the
questionable
bridge getting in the way.
Replace the bridge with a new 3-amp 400-v bridge to give the scope a
little
headroom.


If it is one of the big PS capacitors, you can usually remove them without
removing that side board. They're unsolderable from the bottom, and you
can
usually wiggle them out thru the top opening. You'll need a reasonably
hefty 50 to 100 watt soldering iron to heat up all those wide traces and
semi-massive capacitor lugs.

You'll have a bit of trouble finding an exact replacement, they don't make
a
lot of those traditional FP-based caps anymore. You may have to cobble in
a
newer capacitor. It's a bit of a pain, as Tek for some reason depended
on
the 3 ground lugs of the FP capacitor to act as current-carrying
conductors.
You may have to patch in a few jumper wires to restore continuity there.


Good Luck,


George

Thanks a lot for the detailed info, George, I really appreciate it. I'll
yank a couple of those bridges as you suggested and let you know how it
goes. Thanks again. ---John