Commodore PET 4032 apparent 6520 failure - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

ScottishColin · 19th Oct 2023, 11:28 pm

Here's a video showing one method of wiring up a reset switch:

https://youtu.be/SoRSKqf_R-E?si=y88OEfMVqFYoIol3

And here's a button holder for either a single button or two reset and monitor):

http://tech.guitarsite.de/petcbm_buttonh.html

So it seems there's a couple of choices for the reset switch but I'm still not sure about the Diag (monitor) switch.

Colin.

SiriusHardware · 20th Oct 2023, 1:44 pm

Adrian's method is the 'elegant' method of using the switch to manually trigger the power-on reset circuit by shorting its timing capacitor (which in this board looks to be C50, rather than C68 as I guessed earlier).

For the reset switch only, I would get a pair of male-female JST connectors (see attached image) and solder the wire ends of one part to the C50 pads on the underside of the PET PCB and the ends of the other part to the reset switch. If you need to take the main PCB out for any reason you can just disconnect the reset switch by pulling the two connectors apart.

ScottishColin · 21st Oct 2023, 11:50 am

What do you think about using test hook clips as an even more removable solution?

Colin.

SiriusHardware · 21st Oct 2023, 12:09 pm

Perfectly OK as long as you are always diligent about putting them back in the right place whenever you have had them disconnected, and you make sure they can only connect to the points you connect them to and nothing else close by.

It's certainly the path of least disturbance to the original structure, and very easily removable if you decide it offends your sense of originality.

19th Oct 2023, 11:28 pm	#41
ScottishColin Octode Join Date: May 2012 Location: Perth, Scotland Posts: 1,601	Re: Commodore PET 4032 apparent 6520 failure Here's a video showing one method of wiring up a reset switch: https://youtu.be/SoRSKqf_R-E?si=y88OEfMVqFYoIol3 And here's a button holder for either a single button or two reset and monitor): http://tech.guitarsite.de/petcbm_buttonh.html So it seems there's a couple of choices for the reset switch but I'm still not sure about the Diag (monitor) switch. Colin.

20th Oct 2023, 1:44 pm	#42
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,082	Re: Commodore PET 4032 apparent 6520 failure Adrian's method is the 'elegant' method of using the switch to manually trigger the power-on reset circuit by shorting its timing capacitor (which in this board looks to be C50, rather than C68 as I guessed earlier). For the reset switch only, I would get a pair of male-female JST connectors (see attached image) and solder the wire ends of one part to the C50 pads on the underside of the PET PCB and the ends of the other part to the reset switch. If you need to take the main PCB out for any reason you can just disconnect the reset switch by pulling the two connectors apart. Attached Thumbnails

21st Oct 2023, 11:50 am	#43
ScottishColin Octode Join Date: May 2012 Location: Perth, Scotland Posts: 1,601	Re: Commodore PET 4032 apparent 6520 failure What do you think about using test hook clips as an even more removable solution? Colin.

21st Oct 2023, 12:09 pm	#44
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,082	Re: Commodore PET 4032 apparent 6520 failure Perfectly OK as long as you are always diligent about putting them back in the right place whenever you have had them disconnected, and you make sure they can only connect to the points you connect them to and nothing else close by. It's certainly the path of least disturbance to the original structure, and very easily removable if you decide it offends your sense of originality.