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Commodore Pet 8032

B

banedon

New Member
Joined
Jan 24, 2016
Messages
8
Hi guys

I purchased a Commodore Pet 8032 today, got it home, turned it on and, apart from a few key switches which need l looking at, it seemed to work fine. Unfortunately after 10 mins of so it went bang with lots of smoke. Given the age of the unit I suspected the PSU so took the Pet apart and found the culprit: a 4 wire-input capacitor-like cylinder securely mounted beneath the transformer. I've posted a picture of it below. The markings seem to have come off at some point.
Can anyone tell me what it is and what I can replace it with? I know a small amount about digital electronics, but less about analogue and power.
Any help much appreciated.

pet8032.jpg
 
That's the mains filter capacitor, a common death on these things. As far as I know the thinking these days is it's pretty much redundant since the devices that caused mains spikes big enough to reset a machine of that vintage disappeared a long time ago.

I recently removed the one from my 8096-SK before it could perfume my house and rewired the mains input box so the live feed was switched and fused and the neutral went straight through. Should've documented it I suppose, but I didn't expect anyone else to have the same problem before I got around to doing my 3032 which also has said exploded can. I'll photograph the results and post, the wiring's easy enough to follow.

W
 
Witchy said:
That's the mains filter capacitor, a common death on these things. As far as I know the thinking these days is it's pretty much redundant since the devices that caused mains spikes big enough to reset a machine of that vintage disappeared a long time ago.

I recently removed the one from my 8096-SK before it could perfume my house and rewired the mains input box so the live feed was switched and fused and the neutral went straight through. Should've documented it I suppose, but I didn't expect anyone else to have the same problem before I got around to doing my 3032 which also has said exploded can. I'll photograph the results and post, the wiring's easy enough to follow.

W
Click to expand...

Thanks, Witchy. I thought it was something like that at first, but as it has 4 wire connections and as I've never seen a capacitor with that many I thought it was something else. Filter cap blowing is something that's happened on my various BBC Micros lol.
If I wanted to actually replace the cap, what would you suggest? Do you have the make and model? I have no info/schematics to go by at the moment.
 
it's actual part number is F11.171/65 and here's a bloke who removed one on his CBM 610. I tried following Dave's pictures that you linked to above until I realised all that's needed is a switched live. Mike's blog is the closest to what I actually did.

If you want my unexploded one you can have it ;)

W
 
Isn't it a capacitor (blue wires) and a coil (black wires) combined?

The blue wires are connected to live / neutral and the black wires are in series in the live feed.

And doesn't the capacitor act to reduce contact arcing inside the switch (as well as filtering the mains)?
 
RFI filtering was to keep your computer from broadcasting RF patterns into your neighbor's analog television and AM radio. AC power lines in the house make great RF antennas.
 
I've ordered the unit suggested in Atmotan's thread - I don't want to be sending messages using TCP/RF over my neighbours fillings ;)

BTW here's my PET working (before it blew the filter cap and shorted my mains :p):
cpet.jpg
 
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Yea, I was kind of sarcastically making the point that RFI filtering really isn't necessary anymore in our modern information age ...
 
The RF filter into my 8032 exploded when I was with my head few inches from it... it was like a bomb, LOL, I almost fell from my chair. A lot of smoke and smell.

I simply removed it, no reason to put another. I also removed the other filters from my PETs. No reason to risk an heart attack again ;-)
 
retrogear said:
Yea, I was kind of sarcastically making the point that RFI filtering really isn't necessary anymore in our modern information age ...
Click to expand...

Ok... But I think sarcasm isn't really necessary here. :D

Maybe I should remove mine (or at least disconnect the capacitor). I can imagine a pretty big explosion what with it being so well sealed up in a strong metal can. Normal RIFA caps just make a hissing noise and let out a load of smelly white smoke over a second of two. I can imagine it's not usually explosive, because they have plastic cases that can expand and crack gradually, thus avoiding a pressure build up. That said, I've only experienced it once (on a BBC Micro; well known for it).
 
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Erm can I do a quick check with you folks? I'm putting my PET back together without the filter cap for the moment, but have a doubt as to where the black fly lead from the big copper coloured cap goes. I'm 95% sure it goes to the corner mainboard standoff nearest the transformer (underneath the board) - or the earthing post next to it.

IMG_6105.jpg
 
JonB said:
Yes, it is the ground (at least, on mine it is!)

:)
Click to expand...

Cheers for confirming that :).

My 8032 is now back up and running. I'll put the filter module in when it arrives, but mean while time to have a play.

Thanks to all who helped!
 
And here's the filter fitted. Just got to figure out how to anchor to prevent flapping in the breeze. Unfortunately, the holes in the filter are a little too small for the existing screws/bolts in that area. Perhaps a standard adhessive pad.

IMG_6161.jpg
 
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