Thanks David and Tom-
Any idea about where to start looking for why there's no trace/BF?
I did as Tom suggested and tweaked the R1513 to put it at exactly -50V. Now the readings are:
+15V = +15.08
-15V = -15.00
+50V = +50.0
-50V = -50.0
+5V = 5.2 to 5.5 fluctuates
-17V = -17.9
-54V = -57.6
+54V = +57
+17V = +18.32
+130V = +128.9
Keith
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--- In TekScopes@..., David <davidwhess@...> wrote:
The 7904 I just got and one of my 7834s sort of do the same thing.
With the 7904, the more power the plug-ins draw the more likely it
will tick a couple times when cold starting. The 7834 occasionally
drops into tick mode and then recovers in a few seconds.
Given their age, I am planning on doing a general electrolytic
capacitor replacement in the power supply on both of them.
On Fri, 29 Jun 2012 16:34:12 -0000, "keithostertag"
<keitho@...> wrote:
More news on this ongoing project.
Short story- after replacing a cap in the -54V circuit (C1364) the PS would finally start working. This is with the PS connected normally to the mainframe. That's all connectors connected normally, no dummy loads. There's no trace, no beamfinder, and I still have regulated circuits to fix, but the PS is running and I have GRAT lights and indicator lights on the plugins working.
Here's the odd thing now- If I power up with no plugins loaded (cold, first thing in the morning) it takes 3.5 minutes of being in tic mode before it finally starts working. If I power off, install two plugins, then power on again, it stays in tic mode. If I instead power up with no plugins but let it run for about 5 minutes, then power off and install plugins immediately, when I then power on it works. If I then let it run for awhile I can power off then on and it will work immediately. It is as though something has to warm up before it will work. Any ideas of what that might be? Would it necessarily be a transistor? Could you give me a few ideas of where/what to check?
Here's some approx peak pulse readings when it is tic mode:
from P1452(red)
pin1 (-17V) = -18
pin3 (+54V) = +57
pin4 (+17V) = +18
pin6 (-54V) = -57
P1454 (yellow) pin4 (+130V) = +130V
Here's steady state readings with DMM at SENS TP's
+15V = +14.9
-15V = -14.82
=50V = +49.4
-50V = -49.4
+5V = +5.36
and +5L = +4.94
Still need to fix that +5V circuit... could it be connected with this current problem? Getting parts (I hope) this weekend.
BTW- although C1364 is in the -54V circuit, the same winding off the secondary is used by the -17V circuit . It was the -17V line that was requiring a heavy load to maintain balance (with +5L) at pin2.
Also, I have not yet studied the CRT circuit.
Thanks,
Keith Ostertag
