UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Computers

Notices

Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

Reply
 
Thread Tools
Old Today, 3:22 pm   #241
ScottishColin
Tetrode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 93
Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by dave cox View Post
No problem, PM me if required.

ATB
Thanks Dave. Off to test as above right now.

Colin.
ScottishColin is online now   Reply With Quote
Old Today, 8:35 pm   #242
ScottishColin
Tetrode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 93
Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by Timbucus View Post
Nothing is dumb - just do it once or if you change from x1 to x10 settings as it calibrates the probes. You would also need to do it again if you bought new probes - also try to use the same probes on each port as the trim will be different for each port. This means you match a probe to a port
Thanks. When I have been measuring frequencies with the scope, the first graph I put into the doc is what you have suggested - a squared off measurement before I start measuring the PET.
ScottishColin is online now   Reply With Quote
Old Today, 8:36 pm   #243
ScottishColin
Tetrode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 93
Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by Timbucus View Post
Did you notice that on the scope screen there is a setting that allows you to say if the probe is in X1 or X10 switch position - this will mean that the displays read correctly - in your document to ensure we are reading the values correctly can you confirm that option was set by you - if not we will just adjust the values manually when looking.
Evening - I have not been setting any 1x or 10x setting on the probe software - just letting the AUTO do its job. I will follow your suggestions in post 233 from now on.
ScottishColin is online now   Reply With Quote
Old Today, 8:37 pm   #244
ScottishColin
Tetrode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 93
Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by Mark1960 View Post
Quote:
Originally Posted by SiriusHardware View Post
I guess we had better check for +Ve supply to the CPU since it seems so dead, so Colin, as well as re-checking the voltage on pin 40 (reset) could you also look at the voltage on pin 8 (should be +5V). Although the clock is getting through from one side to the other, that might happen even if the IC was not powered. I'm thinking possible bad socket contacts or missing supply due to damage by damp / corrosion.
As the 6502 is socketed its probably worth removing it from the socket, checking the condition of the pins and then refitting the 6502.

For the scope settings I would suggest starting with 500ns per division and widen out to about 5us per division.

If you don’t see a trace on the scope try adjusting the trigger level, ;keep it on auto might be easiest.

Did the pet have more than one 5v supply? Some of the older systems needed too much current for a single regulator.
I have removed the 6502 and checked the pins - they all look OK to me with no sign of corrosion or pitting.

Pin 40 gives me 5.135V

Last edited by ScottishColin; Today at 8:46 pm.
ScottishColin is online now   Reply With Quote
Old Today, 8:45 pm   #245
ScottishColin
Tetrode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 93
Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
I guess we had better check for +Ve supply to the CPU since it seems so dead, so Colin, as well as re-checking the voltage on pin 40 (reset) could you also look at the voltage on pin 8 (should be +5V). Although the clock is getting through from one side to the other, that might happen even if the IC was not powered. I'm thinking possible bad socket contacts or missing supply due to damage by damp / corrosion.
Pin 40 gives me 5.135V
Pin 8 gives me 0.81 V

And since removing the 6502 to check the legs for any signs of corrosion, I'm no longer getting any frequencies from pins that I was getting frequencies from before (pins 3, 37 & 39)....

I was careful and did earth myself whilst removing/checking, but this feels like a step backwards now.

Despondent of Perth.
ScottishColin is online now   Reply With Quote
Old Today, 9:09 pm   #246
ajgriff
Octode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 1,620
Default Re: Non-working Commodore PET 3016

Don't be despondent Colin. The fact that you haven't got 5V on pin 8 means that the the 6502 doesn't have power and it won't do much without it. Could be a number of causes but the most likely is a poor connection between pin and socket (assuming that you measured the voltage at the pin itself).

Alan
ajgriff is online now   Reply With Quote
Old Today, 9:30 pm   #247
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,627
Default Re: Non-working Commodore PET 3016

From what I've seen on YouTube, Commodore motherboards are notorious for using really cheap IC sockets that only make contact on one side of the pin. Unseating and reseating a chip from one of these can make things worse, not better.

If you fit turned-pin replacements, it might be worth stacking an extra socket into each one just in case; it's a much messier job to remove one of these from a double-sided board if you damage it.
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments.
julie_m is online now   Reply With Quote
Old Today, 10:10 pm   #248
Slothie
Heptode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 655
Default Re: Non-working Commodore PET 3016

With replacing big connectors in frail boards I sometimes use cutters to break up the plastic and desolder the pins one at a time.
Slothie is online now   Reply With Quote
Old Today, 10:12 pm   #249
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 5,360
Default Re: Non-working Commodore PET 3016

The reading Colin has on pin 8 says there is no power to the CPU power pin, it shouldn't take too much to find out why that is. As others have said (and was mentioned somewhere way back in this thread), PETs have a reputation for bad / unreliable IC sockets.

Colin is now, probably always was quite good at reading circuit diagrams and especially good at making continuity measurements, so the next thing we need him to do is to put the CPU back in the socket and (with power off) begin looking for continuity from each CPU pin to one other thing which that CPU pin should be connected to according to the diagram. Note down any which don't appear to be connected to where they should be.

It might ultimately be necessary to replace all of the sockets, but we'll cross those bridges one at a time.
SiriusHardware is online now   Reply With Quote
Old Today, 10:40 pm   #250
ScottishColin
Tetrode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 93
Default Re: Non-working Commodore PET 3016

Thanks all. I did measure the voltage at the pin, so that's a true reading from the 6502's perspective.

I've ordered some 40 pin turned-pin sockets from Cricklewood Electronics in case I need them and I'll get on with chasing the continuity tomorrow.

Thanks all.
ScottishColin is online now   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 10:57 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.