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.

Closed Thread
 
Thread Tools
Old 14th Oct 2021, 9:31 pm   #101
retromit
Pentode
 
Join Date: Oct 2021
Location: Falkirk, Scotland, UK
Posts: 140
Default Re: Commodore PET 2001 voltage regulators

Okay, I've taken all the RAM out that I can and it has been run through the 4116 Arduino tester. Each chip passed the tests successfully, and I ran the tests twice. So it looks like some good news that the RAM looks to be okay. I haven't been able to test the unsocketed one, but I did check the voltages when they were all back in place and they all read the same values.
retromit is offline  
Old 14th Oct 2021, 10:21 pm   #102
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,257
Default Re: Commodore PET 2001 voltage regulators

For a really cheap logic analyser you could get one of the FX2LP boards. I tried an 8 channel Saleae clone but couldn’t get it working with sigrok pulseview or saleae logic, but the FX2LP board was easy to get connected to sigrok pulseview using only the pulseview drivers and zadig and has 16 channels available, though I haven’t used it much yet.

https://m.media-amazon.com/images/I/..._AC_SX679_.jpg

The link is just an example, I got a couple of these cheaper than that on aliexpress, but you might find faster delivery from amazon or ebay.

You would also need some dupont cables to clips for connection to ic pins.

It won’t be as good as a scope for finding bad signal levels, but probably ok to check the input and output of data bus buffers.
Mark1960 is offline  
Old 14th Oct 2021, 10:40 pm   #103
ScottishColin
Octode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 1,762
Default Re: Commodore PET 2001 voltage regulators

I'm pretty sure the Pi can only cope with 5v, so we'd need to be careful with that.

Colin.

Quote:
Originally Posted by SiriusHardware View Post
Agree, since you are lucky enough to have nearly all of the RAM in sockets, by all means test all of the removable RAM in your tester.

If that doesn't score a lucky hit, we may very quickly get to the point where you will need a scope of some sort - a PC-based digital storage scope like the one Colin suggests is ideal and it's fair to say we would not have made any headway with the fault on his PET had he not taken the plunge and bought that. As he said, although the initial outlay is not insignificant, a storage scope is the single most useful bit of test gear you can own and it will continue to be useful for other jobs long after the PET is up and running.

I think there is something called a Pi-Scope which is a bit of hardware and software you add to a Raspberry Pi which effectively makes it into a digital scope - I have no experience with that system personally, you'd have to do some research.

However - as I'm very fond of saying, always try the things you can try with what you already have and costs nothing, so test those RAM ICs first and report back.
ScottishColin is offline  
Old 14th Oct 2021, 11:46 pm   #104
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,471
Default Re: Commodore PET 2001 voltage regulators

Quote:
Each chip passed the tests successfully, and I ran the tests twice. So it looks like some good news that the RAM looks to be okay
That's good news although it does leave a big, huge arrow of suspicion pointing at the one you couldn't test (kidding - if the rest are OK then that odd man out is... probably... OK). To be honest I'm not really surprised, after Colin's RAM survived Chip Armageddon.
SiriusHardware is offline  
Old 14th Oct 2021, 11:51 pm   #105
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,471
Default Re: Commodore PET 2001 voltage regulators

Quote:
I'm pretty sure the Pi can only cope with 5v, so we'd need to be careful with that.
Did you mean 3V?

The scope add-ons for the R-Pi are a bit like the 'box' part of your scope, they handle the possibly unfriendly voltages from the target system and convert them into a stream of digital data which is OK for the Pi. I wouldn't advocate trying to use the GPIO pins of a 3V Raspberry Pi to read the logic levels from a 5V target system directly.
SiriusHardware is offline  
Old 15th Oct 2021, 1:50 am   #106
FrankB
Heptode
 
Join Date: Oct 2005
Location: Olympia, Washington, USA.
Posts: 662
Default Re: Commodore PET 2001 voltage regulators

If this is of any help:
Howard W. Sams publishing put out a service manual for that computer back in the 80's.

I was an ASC for CBM way back then. The PET series and the Commodore Vic & C series.
However that being said, I never had any real problems with the CBM computers back when they were new. Yeah- that was 40 years ago. Time sure flies.
Last I remember, Jameco Electronics had the LM323 IC's in their JimPak line. (Which we sold) I would venture a guess Mouser Electronics and Digikey Electronics should still carry them also.
FrankB is offline  
Old 17th Oct 2021, 9:56 am   #107
ajgriff
Nonode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,583
Default Re: Commodore PET 2001 voltage regulators

Just wondering how you're getting on with the PET Tim?

Alan
ajgriff is offline  
Old 17th Oct 2021, 8:46 pm   #108
retromit
Pentode
 
Join Date: Oct 2021
Location: Falkirk, Scotland, UK
Posts: 140
Default Re: Commodore PET 2001 voltage regulators

Hi Alan.

Things have been a bit slow for the last couple of days with being tied up with things at home; so I haven't been able to do too much. I have, however, been having a quick look over oscilloscopes, and looking over Colin's suggestion, have been lookin at the following:

https://smile.amazon.co.uk/Wosontel-...CBYD9M2QFT3E1B

I may also be able to get my hands on an old analogue 'scope this coming weekend from a friend; however, with never using an oscilloscope before, I wonder if the digital one would be better? Any thoughts/opinions would be welcome.

On further work for the PET. You mentioned previously (and I noticed it when removing the RAM to test it) that the motherboard can flex quite a bit. Is it worth taking out all of the existing ROMs which are socketed, cleaning them, and reflowing the connectors on the sockets? Just thinking of other things I can do in the meantime.

Tim.
retromit is offline  
Old 17th Oct 2021, 10:26 pm   #109
ajgriff
Nonode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,583
Default Re: Commodore PET 2001 voltage regulators

No harm in reseating the ROMs (plus the other socketed ICs) just in case. I'd only get the soldering out if you can see evidence of problems I think.

Difficult for me to comment objectively on digital oscilloscopes as I've only ever used the analogue variety. All I can say is that there will be a bit of a learning curve whichever type you're using. On balance it might be a good idea to take up your friend's kind offer as it will give you a good starting point for deciding whether or not to purchase your own. Do you know the make and model number of your friend's scope?

Alan
ajgriff is offline  
Old 17th Oct 2021, 11:17 pm   #110
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,471
Default Re: Commodore PET 2001 voltage regulators

The scope you have linked to looks very similar to ScottishColin's and he made great progress with his PET problem once he had his up and running.

I (personally) have a preference for analogue scopes mostly as they behave generally predictably - for example if the frequency of the signal being looked at is higher than the scope can comfortably resolve, all that happens is that the individual cycles of the waveform end up so close together that the signal just looks like a thick blue or green band - but that is intuitively what you would expect.

Put a digital sampling scope under similar pressure and the display may erupt into a mass of visual artefacts which are not actually present on the original signal. For that reason, I'm not really a fan.

Plus, analogue scopes have pretty much an individual knob for every function and they operate in an ergenomically intuitive way. Digital scopes tend to be more menu driven although the better ones mimic the 'control panel' of a classic scope so that they are easier to use. I would certainly say that using a digital scope is easier if you have already used a basic analogue scope.

However, digital scopes do have one enormous advantage and that is that they can 'freeze' a one-off or one-shot signal event so that you can look at it and take photos of it. Analogue scopes are only really good at displaying repetitive signals.

If you have a way forward which will cost you nothing, in this case the loan of an analogue oscilloscope, then that is surely the sensible thing to try first. If you get to the point where you do need the capability of a digital scope you will find it easier to 'drive' if you have already learned how to use a basic scope.
SiriusHardware is offline  
Old 18th Oct 2021, 9:41 pm   #111
retromit
Pentode
 
Join Date: Oct 2021
Location: Falkirk, Scotland, UK
Posts: 140
Default Re: Commodore PET 2001 voltage regulators

Hi. That's really good to know about the analogue scope. I've also had some further good news about it as my friend says I can now keep it, so that's very generous!. It might not be until next week that I can pick it up, but I can now (at least) start to read the manual (I've founf a copy online). The scope is a Tektronix TAS250 (2 channel, 50MHz). I know I'll be on a steep learning curve with it, so if anyone has any suggestions then that would be great.

I'll carefully lift the socketed chips tomorrow, then clean the sockets with some contact cleaner and see if it helps any. I may also take out the board again to see if there are any potential issues around the sockets, but in lieu of the scope, is there anything else I could potentially be looking at?

Thanks again,
Tim.
retromit is offline  
Old 18th Oct 2021, 10:28 pm   #112
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: Commodore PET 2001 voltage regulators

That's a great 'scope. There are loads of videos on Youtube for beginners and analogue oscilloscopes. But nothing beats just connecting it to something and trying the controls. Once you get the hang of the timebase and triggering the learning curve isn't steep, certainly less than a digital scope which tend to be loaded with features and confusing menus.
Slothie is offline  
Old 18th Oct 2021, 10:31 pm   #113
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,471
Default Re: Commodore PET 2001 voltage regulators

Quote:
anything else I could potentially be looking at?
Not really for now, you are a little bit blind without the means to 'see' what's going on. We may have to ask you to make something called a 'NOP tester' - you might have seen the method discussed in other threads but essentially, it involves disconnecting the CPU from the databus and feeding it with the opcode for a NOP instruction instead - that causes it to generate regular waveforms / pulses on a lot of the system lines and we can get a lot of information from looking at those steady signals, especially if any are not as they should be.

I think to begin with though, we'll just have you start at the beginning of the clock chain and work your way through that because all the waveforms in that area - up to a point - will be nice regular ones even without a NOP test, so following those will give you good early practice with the scope.

I'm just about to gather up the materials to make those test EPROMs but my programmer is in the loft - however I do have another pressing reason to go up there so I will get it down tomorrow evening and bake those tomorrow night.
SiriusHardware is offline  
Old 18th Oct 2021, 11:02 pm   #114
retromit
Pentode
 
Join Date: Oct 2021
Location: Falkirk, Scotland, UK
Posts: 140
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by Slothie View Post
That's a great 'scope. There are loads of videos on Youtube for beginners and analogue oscilloscopes. But nothing beats just connecting it to something and trying the controls. Once you get the hang of the timebase and triggering the learning curve isn't steep, certainly less than a digital scope which tend to be loaded with features and confusing menus.
Hi. That's really good to know about the scope. I'll certainly have a look around YouTube, but yes, really looking forward to getting it and using it on the PET. Again, it's something new to learn so looking forward to it! I might have a lot more questions, though!
retromit is offline  
Old 18th Oct 2021, 11:05 pm   #115
retromit
Pentode
 
Join Date: Oct 2021
Location: Falkirk, Scotland, UK
Posts: 140
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by SiriusHardware View Post
Quote:
anything else I could potentially be looking at?
Not really for now, you are a little bit blind without the means to 'see' what's going on. We may have to ask you to make something called a 'NOP tester' - you might have seen the method discussed in other threads but essentially, it involves disconnecting the CPU from the databus and feeding it with the opcode for a NOP instruction instead - that causes it to generate regular waveforms / pulses on a lot of the system lines and we can get a lot of information from looking at those steady signals, especially if any are not as they should be.

I think to begin with though, we'll just have you start at the beginning of the clock chain and work your way through that because all the waveforms in that area - up to a point - will be nice regular ones even without a NOP test, so following those will give you good early practice with the scope.

I'm just about to gather up the materials to make those test EPROMs but my programmer is in the loft - however I do have another pressing reason to go up there so I will get it down tomorrow evening and bake those tomorrow night.

That all sounds fine, so I'll also start to look over details for the NOP tester.

Thanks once again for the offer of the EPROMs; it's very good of you.
retromit is offline  
Old 18th Oct 2021, 11:09 pm   #116
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,471
Default Re: Commodore PET 2001 voltage regulators

Ah, one question about your scope, does it include probes? Ideally two, as we may ask you to look at two signals one above the other sometimes - you may possibly even require three probes from time to time as your scope has an 'Ext Trig' input which will allow us to use a third signal to trigger from.
SiriusHardware is offline  
Old 18th Oct 2021, 11:12 pm   #117
retromit
Pentode
 
Join Date: Oct 2021
Location: Falkirk, Scotland, UK
Posts: 140
Default Re: Commodore PET 2001 voltage regulators

I believe it has two probes with it, but I can certainly confirm this tomorrow.
retromit is offline  
Old 18th Oct 2021, 11:38 pm   #118
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: Commodore PET 2001 voltage regulators

Latest version of Pettest

This version shows each block as it is tested.
If the Zero Page and Stack are OK, the I/O chips are initialised as they are by the ROM.
There is a 0-9 counter in the top right of the screen that is incremented by the timer interrupt, to show that is working.
Pressing a key shows which bits on the scan matrix are pressed.

If it fails it keeps writing to the "failed" memory location so the waveforms can be traced.

Video: https://youtu.be/wZO_x-6KVX4

Quote:
Originally Posted by retromit View Post

That all sounds fine, so I'll also start to look over details for the NOP tester.

Thanks once again for the offer of the EPROMs; it's very good of you.
Attached Files
File Type: zip petdiag_02a.zip (5.1 KB, 48 views)
Slothie is offline  
Old 18th Oct 2021, 11:46 pm   #119
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,471
Default Re: Commodore PET 2001 voltage regulators

That was fast! I take it this one is also designed to run in the UD9 position, like the previous version? Oh -

Quote:
If it fails it keeps writing to the "failed" memory location so the waveforms can be traced
Does it keep writing to and reading FROM the failed location, as per the previous version? That is especially useful when looking at the (bidirectional) data bus buffers.
SiriusHardware is offline  
Old 18th Oct 2021, 11:52 pm   #120
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by SiriusHardware View Post
That was fast! I take it this one is also designed to run in the UD9 position, like the previous version? Oh -

Quote:
If it fails it keeps writing to the "failed" memory location so the waveforms can be traced
Does it keep writing to and reading FROM the failed location, as per the previous version? That is especially useful when looking at the (bidirectional) data bus buffers.
Hmm I checked... If the error is in ZP or Stack then yes. Otherwise it doesn't, because its doing the keyboard test. However if the buffers are bad, I would imagine a fail of the ZP or Stack test is guaranteed.

The ROM goes in the F800 slot. If you have a 4K ROM put in 2 copies into the F000 slot.

Last edited by Slothie; 18th Oct 2021 at 11:53 pm. Reason: Location, location, location.
Slothie is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:59 am.


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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.