5971 MSD Top plate - Burnt capacitor identification help

[flowster]

Dear fellow chromatographers,

just recently I started running into problems with my old workhorse HP MSD 5971.

I constantly get a MSD Error 8 - "There is no emission current", normally related to a burnt filament. Checked both, both are okay.
Checked the 74VDC on the FIL A and FIL B test points on the top plate, checked resistance between FIL and FILA/B, everything seems to be fine.

Today I removed and disassembled the top plate. What I found just checking the hardware for obvious signs of problems is:

a heavily burned capacitor labelled C3 on the High Voltage generating side of the top panel, sitting in between a IC labelled U1 and a big red thing labeled L1:




Now I know I am sort of asking for help on a dinosaur, but until now it was working okay, and I love my little machine. Also I am privately running this unit in my basement with very limited financial assets
Is there maybe someone out there still running or in posession of an 5971 who would know the specifications of that capacitor - or someone might be willing to unscrew the black back cover of the top plate and try to tell me what is written on it? As mine is in ashes I cannot get any specs for a replacement to solder in. Or even better anyone knows a person who might know why this little thing burnt - and what to do against that? Maybe it's just age - maybe it's a bigger problem?

Passionately awaiting any little hint helping to narrow this problem down,
Thanks so much,

Florian

[James_Ball]

Will these help?





I hope these upload. I dug up my old hardware manual. Probably the last instruments they actually sent out schematics for the electronics in, the newer ones just don't have this information in them any more.

[flowster]

Dear James, thanks for the effort, I found these in my manual as well - however they seem to be very general with no actual values of the capacitors onboard. I am still hoping for someone out there with a top board who might be willing to take a glance under the hood. In my opinion it should either be a ceramic capacitor with

JK5
9441

or a

K5R
104K

printed on it...

[uzman]

104K means 100 nF ( nanofarad ) capacitor.
If you are planning to replace it , try a high voltage type , at least 600 volts , it may be a part of oscillator circuit and must handle high voltage peaks.

Before re-energize you must also check the other components on the circuit board.

[flowster]

Dear Uzman,

thanks a lot for your help! I am going to give it a try and report

[flowster]

Just a quick update, for all that might experience the same issue: I replaced the burnt capacitor for a 100 nF kemet ceramic cap as suggested, specifications: C410 100nF/50V 10% X7R, after also receiving help from the guys at kemet, stating it was probably their item nr. C410C104K5R5TA. So far everything is back to life Dear Uzman, it seems this one is only rated to 50V, but I will keep an eye on the piece. I think I was heading end of life of the Electron Multiplier, so the HF Voltage went up all the way to 3000V, and when I cleaned the top board and the plate it looked like there might have been some residue around the insulators that might have become conductive, so maybe there was a spike, a spark or something comparable that fried the cap. I cleaned it all up and so far no new issues.
If anything else happens I will update

Thanks everyone so much!

[uzman]

Dear Flowster,

It is nice to hear that the problem is solved !
As you stated , the capacitor might be destroyed because of a voltage spike coming from electron multiplier.

Wish you a problem free days !