Beckman Circuitmate 9020

[Allen49]

While changing some caps on the various boards I noticed one electrolytic capacitor that has on the underside of the board a 10uf 50volt and a 4.7uf 50 volt cap in parallel attached to it. It is a 100uf 35 volt Electrolytic. It does not look like a factory installation but I am unsure. Can anyone tell me if this is common for the
Beckman Circuitmate 9020. Photos and PDF attached.

[kleiner Rainer]

This looks like C923, to be found on page 58 of the PDF, or page 7-7 of the document. It is part of the timebase generator (0.1s per div horizontal range). I would think that someone compensated the loss of capacitance of the original cap instead of replacing it. I own the version sold by Conrad Elektronik in Germany, the VC2040. The original manufacturer seems to be Sampo of Korea (Sampo SS-2020).
I had to replace a CMOS chip in the vertical amp, and to get the circuit board out to do it properly, I would have to dismantle most of the scope - no fun, so I cut off the chip legs and soldered the replacement on top of the pins. Seems that is also the case here: repairing capacitance loss without pulling apart the whole scope.

Greetings,

Rainer DG1SMD

[Allen49]

Thanks a lot for your comments. That was my thought the only problem is that the 100uf 35 volt cap (923) and the other 100uf 35volt cap on the board both test good for capacitance and ESR. I also thought it might be part of the 22nf cap also in the circuit but the 10uf and 4.7uf in parallel does not make sense to me.
I was able to remove the board from the scope by unplugging it, removing the front nut on the panel face and taking the screws out of the  board behind it and moving it to the side a little.

[Allen49]

I was able t find a photo on Flicker from peterkolbe on the Beckman Circuitmate Industrial 9020 and it show two caps on the underside of the time base generator but there is not enough detail to see what they are or how and where they are connected. Photo at below listed link.

https://flic.kr/p/dm5Xcx

[Allen49]

Tried to check and adjust voltages. I was able to adjust the 140 volt supply. I measured 264 volts on the 260 volt test point and also directly off the filter cap from the bridge rectifier but there is no adjustment pot. Would anyone know has to adjust this voltage to 260 volts?

[Chris56000]

Hi!

. . .It's very simple to adjust the 260 V H.T. supply, simply lift one end of R586, get yourself a 20 turn 200K Bourns trimmer pot, set it half–way along its
travel (about 10 turns clockwise from when it clicks at the anticlockwise end), solder the wiper lead and one end lead to the pads for R586, set it to give your 260 V, remove and measure it with a multimeter and fit the nearest fixed resistor to what you measured!

. . .Having said that tho', 264 V is only 1.5% high, which is well within the tolerance most oscilloscope Service Manuals allow for their high–tension supplies!

Chris Williams

[Allen49]

Thank you Chris for your input and advise. I replaced all the Capacitors on the power supply board and several of the 10uf 50volt ones on the other boards. I have been looking for a reason that the square wave from the Calibrator is not exactly square. I was thinking that it may be because of the higher voltage on the 260 volt rail.