PET 2001-N with non-functioning transformer

[Dr. Killemov]

Ok, back from Church. I was streaming both services today - so pressure on!

The schematic for the transformer section is here http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/8032/8032051-3.gif.

Make doubly sure that the mains wiring earth is connected to the PET metal case.

The mains blue wire should be connected to the transformer white wire.

The transformer red wire is unused.

The mains brown wire should be connected to the fuse, that should be connected to the switch, that should be connected to the transformer black wire.

I, personally, would have connected the brown live mains wire to the switch, with the fuse after that...

Do NOT plug it into the mains until we have performed some tests with a multimeter though.

Does this make sense to you?

Dave

Makes perfect sense, Dave. Thank you. I'll go look up those schematics this afternoon.

 

[Dr. Killemov]

Alrighty...mains wiring coming in is as such:

plug is grounded to case with green wire. Transformer is grounded to case at same point with green wire.
Brown wire from cord goes to switch on one side.
Black wire coming from other side of switch goes to fuse.

Black wire coming out of other side of fuse then goes into black wire(mains side) on underside of transformer.

Blue wire from voltage coming in from cord is wired directly to white wire on mains side of transformer.

 

[daver2]

OK, that sounds good.

Switch OFF the PET mains switch.

With your multimeter set to indicate resistance (measuring say 1k Ohm max.) attach the multimeter probes to the LIVE and NEUTRAL pins of the plug top. Do NOT put your fingers near the pins...

This should indicate an open circuit on the multimeter.

Switch the PET mains switch ON. The resistance should drop quite dramatically as indicated on the multimeter.

Switch the PET mains switch OFF. The resistance should indicate open circuit on the multimeter again.

Move the multimeter probes to between the LIVE and EARTH on the plug top. The multimeter should indicate open circuit.

Switch the PET mains switch ON. The multimeter should still indicate open circuit.

Switch the PET mains switch OFF.

Disconnect the multimeter.

Is the transformer disconnected on the secondary windings or not?

Dave

 

[GanjaTron]

Hi everyone, (hi Daver2, long time no hear!)

I hope you got the new year off to a good start. Has there been an update on this elsewhere that I missed? I hope Dr. K. is doing OK.

I just did similar poking around my PET 2001 after its transformer acted up too, emitting a horrible drone when powered up. It turned out that the big blue 27000µF Mallory CGS cap (already mentioned in this thread) had died. My ESR meter indicated it was leaky, and my multimeter even revealed a dead short -- surprisingly, this didn't trip the fuse! I found an identical cap in my 4040 floppy, which measured the same. Incidentally, the longer, thinner 23000µF caps in my 3032 and 8032 are still ok.

Btw, the red wire on the transformer primary is connected on European models, so I assume this is the 220V tap, while the black (disconnected on mine) is the 110V centre tap.

I would check the transformer secondary next, namely continuity between the two brown/red writes on transformer posts 4 and 6.

 

[GanjaTron]

P.S. The fuseholder on my 2001 broke in half when I removed the fuse to check it, exposing the metal contacts! Be sure to check that. Apparently the plastic shell gets brittle with age. This is the main reason I had to disconnect and remove the transformer.

 

[daver2]

Hi GanjaTron,

Yes, long time no hear... Happy New Year.

I fear he has disappeared. Last seen in October I am afraid...

Dave

 

[GanjaTron]

Hi Dave, thanks and new year's greetings to you too!

Indeed, it looks like we've lost Dr. K. How depressing. Was really looking forward to figuring out what's up with that transformer.

--Roland