"Bob" wrote in
:


"bz" wrote in message
98.139...
Have had this 545 sitting, unused, for years, in my utility room.
Bought it
surplus for 50 bux about 20 years ago. IIRC, it 'used to work fine'.

I wheeled it into my ham shack last week, and turned it on. The trace
was too bright and would not turn down completely. After a few minutes,
it shut
down. Found that the FAN mounts had deteriorated and the cooling fan
was not turning. After making new fan mounts and digging lots of small
pieces of aluminum (from the fan hitting the filter) out of the scope,
I turned it
on again. Still too bright. Focus/astigmatism are poor also.

Beam blanking seems to be working as the spot goes away when there is
no sweep.

Checking voltages, the 220 volt test point on the upper right side is
only about 135. Other voltages (500, 350, 100, -150) are all good.


There's your starting point - if the power supplies are way off that can
cause a lot of problems. Get your 220 supply back within specs and see
how the scope works. From what I remember, the -150 is the reference
supply that the rest are set to.

Granted, there could be something elsewhere in the scope loading down
the 220V power supply (leaky caps, etc.) but it's the place to start
troubleshooting.


Smurfies law.... I pulled tubes and tested them. When I put them back in, I
couldn't even get the -150 to adjust at all. Maybe I should not have
'straightened the pins' on the tubes. Maybe I have some sockets that are
not making good contact with straight pins.

The russian 12ax7 doesn't help either.

Now, the -150 is about -87 volts and only a very small adjustment range.
The 100 volts is about 130

Looking at resistances, I am seeing a 100 ohm 'load' to ground on the 100
volt line. That CAN NOT be right. That would require a 100 ohm 100 watt
resistor and there is no such animal.

I was afraid of the bright beam damaging the CRT, even when 'off screen' so
I tried removing the CRT's socket. BAD idea. No load on the HV supply
allows the voltage to go very high and the scope protests with pops and
crackles.

Current plans are to track down the 100 ohm 'short'(or find something that
justifies it),


Bob









--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap