GW GOS 3310 oscilliscope

[Mohntr]

yec oil-con 0.5 uf 1500wvdc capacitor:

Hi, I pulled the cover on my old scope and was checking for swollen caps and I indeed found 1 that is swollen on the end where the single wire comes out. It also appears it has been hot and the plastic label on it has deformed/shrunk.
I googled the cap name and number and don't seem to be able to find a replacement. I have never seen a cap like these and assume it is NOT an electrolite ?
Could anyone offer advice on finding one or should I make it a paper weight? I was hoping to learn how to use it.

Thanks,

Mohntr

[petehall347]

Re: GW GOS 3310 oscilliscope

post a picture of it

[Mohntr]

Re: GW GOS 3310 oscilliscope

Here is a picture.

[R_J]

Re: GW GOS 3310 oscilliscope

It is highly likely the cap is ok, it is just the heatshrink on the cap has shrunk due to heat from the 3 thermistors next to it. I believe those are oil filled caps. If the scope is working leave those caps alone. they will likely out last the scope.

[Topcat]

Re: GW GOS 3310 oscilliscope

It is highly likely the cap is ok, it is just the heatshrink on the cap has shrunk due to heat from the 3 thermistors next to it. I believe those are oil filled caps. If the scope is working leave those caps alone. they will likely out last the scope.

I'm inclined to agree.

[Mohntr]

Re: GW GOS 3310 oscilliscope

Thanks for replying. The scope is not acting right. It only works for the first 30 seconds or so when I turn it on. When reading the 0.25v internal calibration it is smooth then all of a sudden starts acting erratic and the line is fuzzy, I only opened the case to look for something obvious and that one cap had the deformed sleeve and the end not showing in the picture is swollen compared to all the others next to it.
I could snip one leg out of circuit and test with a meter, but I dont have an esr meter.

[stj]

Re: GW GOS 3310 oscilliscope

probably a bad diode in the HV circuits

[redwire]

Re: GW GOS 3310 oscilliscope

Just lift a leg and test the capacitors' value and for leakage. I see oil-filled capacitors in oscilloscope HV section just don't last. Marcon's in Leader oscilloscopes are notorious for failing. Then they take out the HV rectifier and it's a mess.
If the trace is going fuzzy, then the focus voltage is likely sagging so I would suspect a power supply problem. The three MOV's next to it are typically a shunt-regulator for the high voltage but nothing hot enough to heat up a big can and shrink the heatshrink lol

P.S. When working with the HV capacitors, always discharge them first.

[R_J]

Re: GW GOS 3310 oscilliscope

If the cap is swollen at the end that is not shown in the picture, then replace the 3 of them.

[Mohntr]

Re: GW GOS 3310 oscilliscope

Thanks for the info, I'll get a picture of the end of the cap after work this evening. I appreciate the help.

[redwire]

Re: GW GOS 3310 oscilliscope

The Marcon brand ones have a hard epoxy seal and no rubber bung.
These old axial caps have no safety vent, but I don't think the oil actually makes gas, unlike electrolytics. I'm not sure what the electrolyte actually is.

[stj]

Re: GW GOS 3310 oscilliscope

pcb's ??
like transformer-oil??

[redwire]

Re: GW GOS 3310 oscilliscope

Electrolytics can't go higher than around 450-500VDC, so for big HV caps I guess oil was used.
I haven't taken one apart, but yes oil like motor starting caps. Some Marcon's have a rubber bung, others have epoxy. The bumble bee capacitors were castor oil.

Three of 0.5uF 1500V C101, C102, C103 are the voltage-doubler and I see a fourth smaller one in OP's pic. I'd just change all of them, put in polypropylene parts from digikey or mouser.

[Mohntr]

Re: GW GOS 3310 oscilliscope

https://www.dropbox.com/preview/Publ...?role=personal

[Mohntr]

Re: GW GOS 3310 oscilliscope

https://www.dropbox.com/s/joisx5n6z3...22017.jpg?dl=0

another image, sorry for the two posts.

[Mohntr]

Re: GW GOS 3310 oscilliscope

C102 shows it is shorted to its case. I can not get a reading of any capacitance with my meter on Cap mode. All other caps I get a reading on cap mode.
I have not taken anything out of circuit.
redwire, may i ask where you found the schematic?

[Mohntr]

Re: GW GOS 3310 oscilliscope

I was on Mousers website looking for the polypropylene caps and did not see them. Are they called something else by chance?
I'm learning electronics on my own, I have never seen these types of caps before so I want to get the right one(s). Thank you.

[Mohntr]

Re: GW GOS 3310 oscilliscope

Is this a bad choice?

https://www.ebay.com/itm/2pcs-Bishop...ss!63069!US!-1

[redwire]

Re: GW GOS 3310 oscilliscope

Those eBay caps seem expensive and for audiophile use.

I would consider:
Kemet axial 0.47uF 2000VDC 44mm long 33.5mm dia. Best fit. Mouser has them too.
Wima boxed PP 0.47uF 1600VDC 32mm height.
Kemet R76 series 0.47uF 1600VDC but 37mm high.

The boxed film caps would need HV lead wires added and I glue them to the pcb with some silicone. A bit awkward.

Low cost chinese film caps are called "CBB" but New Years so for 2 weeks shops are closed. I saw 474J 2000V 27mm lead spacing https://www.ebay.com/itm/CBB-Metalli...c/302297220783 $8 for 10.