Denial

Managed to dig my old PET 4032 out of the attic..
Let it stand at room temperature for a few hours ..
Then bit the bullet and powered it up ..
It started ...and was rewarded with a green screen text image ..
left it running for about an hour ...then sadly it died with much acrid smokefrom the mains transformer ..
..which is now sadly dead ..
I suspect the PET is just fine ..but the AC mains transformer needs replacing ..
Not much chance Im guessing ..unless someone knows otherwise ?
240V AC mains primary ...
3 secondaries ..
one is a single winding for the monitor 0 - Xv (thin brown twisted pair) connections labelled 7 & 8
one is a single winding to the main board 0 - Xv (thicker blue pair to pcb molex) connections labelled 9 & 10
finally a 3rd which is X - 0 - X v (brown - black - brown) connections labelled 4 - 5 - 6
Transformer part number 320198-03 made by CHUNG HING INDUSTRY - HONG KONG
Can anyone help here ?
A schematic ...or possibly just AC voltages and currents ?
Better still a vintage transformer rewind service that wont break the bank ?

..maybe someone out there has a working replacement transformer they want to sell ..

rgds
ViperSan

...just a thought ...
but possibly multi output variable voltage switch mode psus could be used instead ..but first I would need to know what voltage and current the 3 supplies to monitor ...and mainboard actually are ?
anyone ?

There is a technical manual and stuff at http://www.zimmers.net/anonftp/pub/cbm/ ... index.html along with schematics for most other CBM computers.

Sorry to hear that. I had a similar experience with my PET 8032 (http://forum.6502.org/viewtopic.php?f=4&t=4586).

However, are you sure it's the AC transformer? Those things are usually pretty stable and last for decades (although, it's been decades since that 4032 was made...).

cbmeeks wrote:Sorry to hear that. I had a similar experience with my PET 8032 (http://forum.6502.org/viewtopic.php?f=4&t=4586).

However, are you sure it's the AC transformer? Those things are usually pretty stable and last for decades (although, it's been decades since that 4032 was made...).

Definately the transformer...
It was belching smoke ...even after I powered down..
I really hope I can fix it ...
It is after all a bit of history...and very collectable.

I suspect shorted turns on the primary winding..

Yes, you should certainly fix it or have it fixed if you can.

Could you post some pics?

cbmeeks wrote:Yes, you should certainly fix it or have it fixed if you can.

Could you post some pics?

I have a couple of pix I took just before it failed ..
I'll add them later ...when I get home from work.

As requested ..some pix of the PET before it failed ..and of the transformer that died..

I have seen exactly what you describe happen and it was the EMI filter capacitor that is in that black box shown in the picture. It looked like the transformer blew because the smoke shot out at the transformer from the box and the smoke lingered around the transformer . When it blew it took out the fuse so the pet was dead. I removed the bad capacitor and replaced the fuse and was back in business..

norm8332 wrote:I have seen exactly what you describe happen and it was the EMI filter capacitor that is in that black box shown in the picture. It looked like the transformer blew because the smoke shot out at the transformer from the box and the smoke lingered around the transformer . When it blew it took out the fuse so the pet was dead. I removed the bad capacitor and replaced the fuse and was back in business..

Worth a look Norm ..
I'll check for filter caps tomorrow..
I can't cross my fingers any tighter..

ViperSan wrote:Managed to dig my old PET 4032 out of the attic..
Let it stand at room temperature for a few hours ..
Then bit the bullet and powered it up ..
It started ...and was rewarded with a green screen text image ..
left it running for about an hour ...then sadly it died with much acrid smokefrom the mains transformer ..

You do know this is the best way to destroy an old computer or any old electronic appliance for that matter, don't you ?

All the electrolytic capacitors have to be replaced or rejuvenated before you power them up.

This is why most well working VIC-20 and C64 purchased on eBay end up in a trash can less than 24H after getting to their new buyers.

Definately the transformer...
It was belching smoke ...even after I powered down..
I really hope I can fix it ...
It is after all a bit of history...and very collectable.

I suspect shorted turns on the primary winding..

I suspect one of the large capacitors connected to one of the multiple secondaries has turned into a short circuit. In turn, this overheated (and possibly destroyed) the transformer.

I think Norm scores points here ...
No obvious caps to replace under that black box next to the transformer ..
but it would seem the filter caps are actually integrated into the rear of the 3 pin socket (mains in) ...
removing the screews an flipping the combo socket shows the internal schematic ...and if you look closely the rear cover which backs onto the mains transformer has split open ..
Not fully removed it yet to look inside ..but I'm guessing Norm is spot on with his diagnosis

It pays not to throw stuff away ..
Robbed this out of an old ATX PC psu ..
Re-assembled and cased should do the job nicely..
rgds
VS

Not much room for manoeuvre in that tight space ..but just managed to fit the pcb ..
I'll pot it up with the hot snot gun ..and mount it back with a plastic insert under the transformer unit to add some isolation in case it moves..
will test without the PET connected later..
rgds
VS

Success !!! ..
thanks again Norm..
All reassembled with new filter ...and working..
Time to start the cleaning process I think..
'HELLO OLD FRIEND - WELCOME BACK'