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 13th Oct 2021, 8:06 pm   #81
retromit
Tetrode
 
Join Date: Oct 2021
Location: Edinburgh, Scotland, UK
Posts: 61
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by SiriusHardware View Post
To try to make things a bit clearer, one of my famous sketches - here we have a stylised drawing of the female contact (shown in dark grey) and the male pin (shown in brown).

Drawing 'A' shows the situation as it may have been originally, with the female contacts in the JP8 plug / connection #4 spread wider apart than they should be so there was no, or intermittent contact with the pin.

'B' shows the situation as it may be now - the contacts have been pushed down a bit so that they now come into contact with the pin, but maybe only just. Any movement of JP8 could make that connection disconnect again.

'C' and 'D' show the contacts more like they should be, close to the pin and touching it all the way down the sides. When like this, the relative height of the contact inside the housing does not matter so much, it will still make contact with the sides of the pin.

Note that the actual contact in the actual plug may only touch the pin on one side, or on two sides (as shown) or it may even be a hollow 'box' which makes contact with the pin on all four sides.

Whatever the actual situation, if the contacts in the female connector have been bent too far apart then they may need to be bent back closer inwards towards the male pin. AJ suggested looking to see if you can get a needle in there to bend them back in, I would also look to see if the contact can be unlatched / unlocked and lifted out of the plastic housing.
Hi. Thanks very much for the diagram/explaination. I've just had another look over the female end of the socket and although there looks to be the contact strips, you can't really move them. I've tried a few times with a sewing needle, but they're not for giving much. I've had a look over the socket as well with regards to unlatching/unlocking; I'll admit I'm not that confident in trying to remove it from the plastic housing, and it does seem pretty stuck. I'm not really too sure what to do. I've tested a few more times with unplugging/plugging, and the PET screen still comes on. It's just the thought in the back of the mind with regards to losing the DC voltage again.

Although the pin/socket is now delivering the voltage, could a safeguard be to have the crocodile clip from the +ve terminal on the large capacitor to CR1/2? Would this cause any additional problems?
retromit is offline   Reply With Quote
Old 13th Oct 2021, 8:07 pm   #82
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,310
Default Re: Commodore PET 2001 voltage regulators

It would do no harm to leave a permanent bypass around JP8 (4) but it would be inconvenient whenever you needed to remove the PCB and a highly unoriginal feature to have in a historic machine.

With the connector fitted and the machine running, what DC voltage do you now see
-On CR1 tapered end
-On top of the JP8 connector (pin 4).

The closer these two voltages are to each other, the better the connection between the JP8 pin and JP8 receptacle.
SiriusHardware is offline   Reply With Quote
Old 13th Oct 2021, 8:16 pm   #83
ajgriff
Octode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 1,946
Default Re: Commodore PET 2001 voltage regulators

Bearing in mind the work carried out and looking at the photos I think this should be fine. Your call of course.

Alan
ajgriff is online now   Reply With Quote
Old 13th Oct 2021, 8:40 pm   #84
retromit
Tetrode
 
Join Date: Oct 2021
Location: Edinburgh, Scotland, UK
Posts: 61
Default Re: Commodore PET 2001 voltage regulators

Hi.

Okay, I took a few measurements over different periods of time and they all seemed to be around the same value. The last two sets I have are as follows:

CR1 = 9.04/3v
CR2 = 9.04/3v
JP8 pin 4 = 9.04v

CR1 = 9.08v
CR2 = 9.06v
JP8 pin 4 = 9.07v

These readings were taken when the PET was first switched on, then after running for a few minutes. I did check CR1 a few times, and if this changed, then I checked pin 4 - they were about in sync value wise from what I could see.
retromit is offline   Reply With Quote
Old 13th Oct 2021, 8:49 pm   #85
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,310
Default Re: Commodore PET 2001 voltage regulators

Those are nice results, little or no voltage drop across the JP8(4) connection now.

I would say you've probably done enough to have confidence in the connection now, especially if the connector has been on and off a few times and still giving good results like that.
SiriusHardware is offline   Reply With Quote
Old 13th Oct 2021, 10:19 pm   #86
ScottishColin
Heptode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 658
Default Re: Commodore PET 2001 voltage regulators

Is it worth doing a continuity test from wherever feeds JP8/4 to wherever it needs to go to (sorry I'm away) and wiggling the plug to see what happens?

It might be worth testing as it's a test without power and therefore can't harm any other ICs.

Colin.
ScottishColin is offline   Reply With Quote
Old 13th Oct 2021, 10:26 pm   #87
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,310
Default Re: Commodore PET 2001 voltage regulators

Decent idea, the test points to check continuity between would be CR1 or CR2 tapered end and the +Ve terminal of the offboard capacitor. It would be difficult to hold the probes in place with one hand each and also wiggle the connector, so maybe use croc leads to attach the meter leads to the test points to free both hands for connector, the wiggling of.
SiriusHardware is offline   Reply With Quote
Old 14th Oct 2021, 1:02 pm   #88
ajgriff
Octode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 1,946
Default Re: Commodore PET 2001 voltage regulators

Iíve been giving some more thought to the next steps now there is more confidence in the security of the JP8/P4 connection. In the absence of an oscilloscope, logic probe or EPROM programmer there are still a few options in terms of eliminating possible reasons for the random character display and consequent failure to boot correctly. In no particular order these are a some of the possibilities which might be worth considering:

1. The 555 (UA2) timer circuit should reset the CPU a couple of seconds after switch on. If this doesnít work correctly the random character screen doesnít clear as highlighted by Slothie earlier. Operation of the circuit can be verified by monitoring the voltage on the reset pin (40) of the 6502 (UC4) CPU at switch on. The voltage should remain at 0V for a couple of seconds before rising to around 4V (steady). Pin 40 is in the top left corner of the 6502 when viewing the board from the opposite side to the power supply.

2. The PET doesnít need the two PIAs (UC6 & UC7) in order to boot but faulty chips can cause the random character screen problem. Switching on the machine with the PIAs removed wonít harm the PET although if it does boot properly neither the keyboard nor the external interfaces will function. This is just a simple way of identifying faulty PIAs.

3. During the work so far there has been quite a lot of board manipulation/flexing and elderly PETs are well known for developing poor IC pin to socket contact. Rather than removing socketed ICs completely (fiddly with a risk of pin damage on re-insertion) Iíd suggest the lift slightly, squirt with contact cleaner, rock and then push home firmly approach. Iíd probably leave the processor and ROM chips alone in the first instance and just concentrate on the 15 socketed DRAMs.

4. In view of the fact(?) that the DRAMs are the only chips which rely on anything other than the +5V supply I still think they are the most likely candidates for damage caused by the JP8/P4 issue. See earlier post. If Sirius is able and willing to provide an EPROM with which to test for individual DRAM failure that would be ideal of course. However there are other ways to at least carry out some checks on the DRAMs. The attached document might help as it illustrates how the dynamic RAM board can be configured to operate with only eight 4116s, albeit at half capacity. With a bit of chip swapping it might be possible to identify groups containing one or more faulty chip(s) and arrive at a set of eight working chips thereby ruling out faults elsewhere on the board.

If none of the above suggestions bear fruit itíll be necessary to start thinking about things like logic ICs, the CPU, ROMs and the like but in view of the previously working nature of the machine Iím hoping that wonít be necessary. Iíve also rather ignored the possibility of supply line failure somewhere along the line for the same reason.

Just throwing out some ideas really to help (hopefully) get us started on the next steps.

Alan
Attached Files
File Type: pdf PET Dynamic.pdf (3.88 MB, 8 views)
ajgriff is online now   Reply With Quote
Old 14th Oct 2021, 3:30 pm   #89
retromit
Tetrode
 
Join Date: Oct 2021
Location: Edinburgh, Scotland, UK
Posts: 61
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by SiriusHardware View Post
Decent idea, the test points to check continuity between would be CR1 or CR2 tapered end and the +Ve terminal of the offboard capacitor. It would be difficult to hold the probes in place with one hand each and also wiggle the connector, so maybe use croc leads to attach the meter leads to the test points to free both hands for connector, the wiggling of.
Hi. Yes, this is certainly something I can check. I'll set something up similar to when I had the clip to provide the voltage (from an earlier post), but to test the continuity. It will hopefully give some more confidence that pin 4 on JP8 is now okay.
retromit is offline   Reply With Quote
Old 14th Oct 2021, 3:37 pm   #90
retromit
Tetrode
 
Join Date: Oct 2021
Location: Edinburgh, Scotland, UK
Posts: 61
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by ajgriff View Post
Iíve been giving some more thought to the next steps now there is more confidence in the security of the JP8/P4 connection. In the absence of an oscilloscope, logic probe or EPROM programmer there are still a few options in terms of eliminating possible reasons for the random character display and consequent failure to boot correctly. In no particular order these are a some of the possibilities which might be worth considering:

1. The 555 (UA2) timer circuit should reset the CPU a couple of seconds after switch on. If this doesnít work correctly the random character screen doesnít clear as highlighted by Slothie earlier. Operation of the circuit can be verified by monitoring the voltage on the reset pin (40) of the 6502 (UC4) CPU at switch on. The voltage should remain at 0V for a couple of seconds before rising to around 4V (steady). Pin 40 is in the top left corner of the 6502 when viewing the board from the opposite side to the power supply.

2. The PET doesnít need the two PIAs (UC6 & UC7) in order to boot but faulty chips can cause the random character screen problem. Switching on the machine with the PIAs removed wonít harm the PET although if it does boot properly neither the keyboard nor the external interfaces will function. This is just a simple way of identifying faulty PIAs.

3. During the work so far there has been quite a lot of board manipulation/flexing and elderly PETs are well known for developing poor IC pin to socket contact. Rather than removing socketed ICs completely (fiddly with a risk of pin damage on re-insertion) Iíd suggest the lift slightly, squirt with contact cleaner, rock and then push home firmly approach. Iíd probably leave the processor and ROM chips alone in the first instance and just concentrate on the 15 socketed DRAMs.

4. In view of the fact(?) that the DRAMs are the only chips which rely on anything other than the +5V supply I still think they are the most likely candidates for damage caused by the JP8/P4 issue. See earlier post. If Sirius is able and willing to provide an EPROM with which to test for individual DRAM failure that would be ideal of course. However there are other ways to at least carry out some checks on the DRAMs. The attached document might help as it illustrates how the dynamic RAM board can be configured to operate with only eight 4116s, albeit at half capacity. With a bit of chip swapping it might be possible to identify groups containing one or more faulty chip(s) and arrive at a set of eight working chips thereby ruling out faults elsewhere on the board.

If none of the above suggestions bear fruit itíll be necessary to start thinking about things like logic ICs, the CPU, ROMs and the like but in view of the previously working nature of the machine Iím hoping that wonít be necessary. Iíve also rather ignored the possibility of supply line failure somewhere along the line for the same reason.

Just throwing out some ideas really to help (hopefully) get us started on the next steps.

Alan
Hi Alan. Thanks for these details. Here's what I've just been through:

- I've just checked the voltage of pin 40 on the 6502 (UC4) and it came out steady at 4.88v. I also tested from a startup, and it went from 0v to 4.88v. I checked it a few times, and it did seem steady at 4.88v.

- I've also removed both the PIAs (UC6 nad UC7), then started the PET up. The screen didn't seem to change (still garbled).

- The 15 RAM ICs have been lifted and contact cleaner squirted around the legs/sockets. They have been seated back in. When switching the PET back on, it still displayed the garbled screen.

- I'll have a read through the document to see if we can progress something with this.

Tim.
retromit is offline   Reply With Quote
Old 14th Oct 2021, 4:38 pm   #91
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,310
Default Re: Commodore PET 2001 voltage regulators

I'm going to program up a 2716 with the 'Daver2' test code and send it off to Tim when it's ready so hopefully that will be available to use as and when we get to the point where we think the system can run some test code.

I may also do a second one with Slothie's code, the only reason that one is not an automatic choice is that I don't have a TMS2532 EPROM to program it into. It's just a lucky fluke that we can plug a 2716 into the UD8 position and it will work, whereas a 2716 plugged into the UD9 socket needs an adaptor to work. I might just 'adapt' a 2716 directly rather than place it in a socket adaptor.

With this one, I think we might have to start quite a long way back on the grid. The normal startup sequence is:
-Jump to boot code in UD9
-Shortly afterwards, jump to a subroutine in UD8.
-In the subroutine,
---Clear the screen RAM
---Initialise the large ICs
-Return from subroutine.

If the main system RAM is faulty then the machine will get stuck because it will fetch an invalid return address from the faulty RAM. But, it should still have managed to clear the screen by this point.

Unfortunately this machine isn't clearing the screen so right now, I'm not sure it will be able to execute test code either, unless we happen to have a dud original UD8 or UD9 PROM - it will still be worth trying one or other of the test EPROMs as a way of ruling out a faulty UD9 or UD8 respectively.

So now we come to the usual questions for retromit: What do you have in the way of test gear, in addition to the meter which you obviously do have..?

-Logic Probe?
-Frequency meter or Multimeter with a 'Frequency' range on it?
-Oscilloscope?
-Logic analyser or logic 'sniffer' with parallel inputs?

-Any other potentially useful test toys such as an Arduino Uno, Arduino Mega or Raspberry Pi?
SiriusHardware is offline   Reply With Quote
Old 14th Oct 2021, 4:40 pm   #92
ajgriff
Octode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 1,946
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by retromit View Post
- I've just checked the voltage of pin 40 on the 6502 (UC4) and it came out steady at 4.88v. I also tested from a startup, and it went from 0v to 4.88v. I checked it a few times, and it did seem steady at 4.88v.
Well at least you've ruled out a few possibilites. Just one question though. Did it take a couple of seconds before the voltage rose from 0V to 4.88V? The delay is important because it allows the system to reach a stable state before the CPU starts its work.

Alan

Last edited by ajgriff; 14th Oct 2021 at 5:06 pm.
ajgriff is online now   Reply With Quote
Old 14th Oct 2021, 4:48 pm   #93
ajgriff
Octode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 1,946
Default Re: Commodore PET 2001 voltage regulators

No frequency measuring option on the DMM Tim is currently using unfortunately. See manual attached to post #42.

Alan
ajgriff is online now   Reply With Quote
Old 14th Oct 2021, 6:08 pm   #94
ajgriff
Octode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 1,946
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by SiriusHardware View Post
If the main system RAM is faulty then the machine will get stuck because it will fetch an invalid return address from the faulty RAM. But, it should still have managed to clear the screen by this point.
Out of interest my 2001-8 with static RAM had several faulty RAM chips which resulted in the screen failing to clear.

Alan
ajgriff is online now   Reply With Quote
Old 14th Oct 2021, 6:57 pm   #95
retromit
Tetrode
 
Join Date: Oct 2021
Location: Edinburgh, Scotland, UK
Posts: 61
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by ajgriff View Post
Quote:
Originally Posted by retromit View Post
- I've just checked the voltage of pin 40 on the 6502 (UC4) and it came out steady at 4.88v. I also tested from a startup, and it went from 0v to 4.88v. I checked it a few times, and it did seem steady at 4.88v.
Well at least you've ruled out a few possibilites. Just one question though. Did it take a couple of seconds before the voltage rose from 0V to 4.88V? The delay is important because it allows the system to reach a stable state before the CPU starts its work.

Alan
Hi Alan,

I've just tested again, and it was around 2 seconds; it went straight from 0v to 4.88v in virtually one jump; then solid on 4.88v.

Tim.
retromit is offline   Reply With Quote
Old 14th Oct 2021, 7:02 pm   #96
retromit
Tetrode
 
Join Date: Oct 2021
Location: Edinburgh, Scotland, UK
Posts: 61
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by SiriusHardware View Post
I'm going to program up a 2716 with the 'Daver2' test code and send it off to Tim when it's ready so hopefully that will be available to use as and when we get to the point where we think the system can run some test code.

I may also do a second one with Slothie's code, the only reason that one is not an automatic choice is that I don't have a TMS2532 EPROM to program it into. It's just a lucky fluke that we can plug a 2716 into the UD8 position and it will work, whereas a 2716 plugged into the UD9 socket needs an adaptor to work. I might just 'adapt' a 2716 directly rather than place it in a socket adaptor.

With this one, I think we might have to start quite a long way back on the grid. The normal startup sequence is:
-Jump to boot code in UD9
-Shortly afterwards, jump to a subroutine in UD8.
-In the subroutine,
---Clear the screen RAM
---Initialise the large ICs
-Return from subroutine.

If the main system RAM is faulty then the machine will get stuck because it will fetch an invalid return address from the faulty RAM. But, it should still have managed to clear the screen by this point.

Unfortunately this machine isn't clearing the screen so right now, I'm not sure it will be able to execute test code either, unless we happen to have a dud original UD8 or UD9 PROM - it will still be worth trying one or other of the test EPROMs as a way of ruling out a faulty UD9 or UD8 respectively.

So now we come to the usual questions for retromit: What do you have in the way of test gear, in addition to the meter which you obviously do have..?

-Logic Probe?
-Frequency meter or Multimeter with a 'Frequency' range on it?
-Oscilloscope?
-Logic analyser or logic 'sniffer' with parallel inputs?

-Any other potentially useful test toys such as an Arduino Uno, Arduino Mega or Raspberry Pi?
Hi,

Many thanks once again for sorting the EPROM for me.

The multimeter I have is a bit basic. It has been planning to upgrade for a while now, so this could be an ideal time. Have you any suggestions on a good upgrade?

Unfortunately I don't have an oscilloscope or logic analyser (but, again, open to any suggesstions you may have). I do have a couple of Raspberry Pis, and also a 4116/4164 RAM tester (which is Arduino based) - which I was thinking of using to test the RAM chips from the PET (the 4116).

Tim.
retromit is offline   Reply With Quote
Old 14th Oct 2021, 7:09 pm   #97
ScottishColin
Heptode
 
Join Date: May 2012
Location: Perth, Scotland
Posts: 658
Default Re: Commodore PET 2001 voltage regulators

As part of my fixing of my dilapidated PET linked to earlier, I had to buy a scope. I bought a generic 6022BL scope off Amazon and it did me fine. About £80-£90 right now. It needs a PC to plug into but I happened to have a spare laptop I could use. It works on Windows 10 and there's a Linux program/drivers for it too.

I learnt a lot about how to use them and still have it at the end of the process. There's plenty of people on here with far more knowledge than I that will have broader recommendations - just thought I'd mention what I used.

Colin.


Quote:
Originally Posted by retromit View Post
Quote:
Originally Posted by SiriusHardware View Post
I'm going to program up a 2716 with the 'Daver2' test code and send it off to Tim when it's ready so hopefully that will be available to use as and when we get to the point where we think the system can run some test code.

I may also do a second one with Slothie's code, the only reason that one is not an automatic choice is that I don't have a TMS2532 EPROM to program it into. It's just a lucky fluke that we can plug a 2716 into the UD8 position and it will work, whereas a 2716 plugged into the UD9 socket needs an adaptor to work. I might just 'adapt' a 2716 directly rather than place it in a socket adaptor.

With this one, I think we might have to start quite a long way back on the grid. The normal startup sequence is:
-Jump to boot code in UD9
-Shortly afterwards, jump to a subroutine in UD8.
-In the subroutine,
---Clear the screen RAM
---Initialise the large ICs
-Return from subroutine.

If the main system RAM is faulty then the machine will get stuck because it will fetch an invalid return address from the faulty RAM. But, it should still have managed to clear the screen by this point.

Unfortunately this machine isn't clearing the screen so right now, I'm not sure it will be able to execute test code either, unless we happen to have a dud original UD8 or UD9 PROM - it will still be worth trying one or other of the test EPROMs as a way of ruling out a faulty UD9 or UD8 respectively.

So now we come to the usual questions for retromit: What do you have in the way of test gear, in addition to the meter which you obviously do have..?

-Logic Probe?
-Frequency meter or Multimeter with a 'Frequency' range on it?
-Oscilloscope?
-Logic analyser or logic 'sniffer' with parallel inputs?

-Any other potentially useful test toys such as an Arduino Uno, Arduino Mega or Raspberry Pi?
Hi,

Many thanks once again for sorting the EPROM for me.

The multimeter I have is a bit basic. It has been planning to upgrade for a while now, so this could be an ideal time. Have you any suggestions on a good upgrade?

Unfortunately I don't have an oscilloscope or logic analyser (but, again, open to any suggesstions you may have). I do have a couple of Raspberry Pis, and also a 4116/4164 RAM tester (which is Arduino based) - which I was thinking of using to test the RAM chips from the PET (the 4116).

Tim.
ScottishColin is offline   Reply With Quote
Old 14th Oct 2021, 7:19 pm   #98
ajgriff
Octode
 
ajgriff's Avatar
 
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 1,946
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by retromit View Post
I do have a couple of Raspberry Pis, and also a 4116/4164 RAM tester (which is Arduino based) - which I was thinking of using to test the RAM chips from the PET (the 4116).
Now that seems like a good place to start!

Alan
ajgriff is online now   Reply With Quote
Old 14th Oct 2021, 7:49 pm   #99
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,310
Default Re: Commodore PET 2001 voltage regulators

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.
SiriusHardware is offline   Reply With Quote
Old 14th Oct 2021, 8:27 pm   #100
retromit
Tetrode
 
Join Date: Oct 2021
Location: Edinburgh, Scotland, UK
Posts: 61
Default Re: Commodore PET 2001 voltage regulators

Quote:
Originally Posted by ScottishColin View Post
As part of my fixing of my dilapidated PET linked to earlier, I had to buy a scope. I bought a generic 6022BL scope off Amazon and it did me fine. About £80-£90 right now. It needs a PC to plug into but I happened to have a spare laptop I could use. It works on Windows 10 and there's a Linux program/drivers for it too.

I learnt a lot about how to use them and still have it at the end of the process. There's plenty of people on here with far more knowledge than I that will have broader recommendations - just thought I'd mention what I used.

Colin.


Quote:
Originally Posted by retromit View Post
Quote:
Originally Posted by SiriusHardware View Post
I'm going to program up a 2716 with the 'Daver2' test code and send it off to Tim when it's ready so hopefully that will be available to use as and when we get to the point where we think the system can run some test code.

I may also do a second one with Slothie's code, the only reason that one is not an automatic choice is that I don't have a TMS2532 EPROM to program it into. It's just a lucky fluke that we can plug a 2716 into the UD8 position and it will work, whereas a 2716 plugged into the UD9 socket needs an adaptor to work. I might just 'adapt' a 2716 directly rather than place it in a socket adaptor.

With this one, I think we might have to start quite a long way back on the grid. The normal startup sequence is:
-Jump to boot code in UD9
-Shortly afterwards, jump to a subroutine in UD8.
-In the subroutine,
---Clear the screen RAM
---Initialise the large ICs
-Return from subroutine.

If the main system RAM is faulty then the machine will get stuck because it will fetch an invalid return address from the faulty RAM. But, it should still have managed to clear the screen by this point.

Unfortunately this machine isn't clearing the screen so right now, I'm not sure it will be able to execute test code either, unless we happen to have a dud original UD8 or UD9 PROM - it will still be worth trying one or other of the test EPROMs as a way of ruling out a faulty UD9 or UD8 respectively.

So now we come to the usual questions for retromit: What do you have in the way of test gear, in addition to the meter which you obviously do have..?

-Logic Probe?
-Frequency meter or Multimeter with a 'Frequency' range on it?
-Oscilloscope?
-Logic analyser or logic 'sniffer' with parallel inputs?

-Any other potentially useful test toys such as an Arduino Uno, Arduino Mega or Raspberry Pi?
Hi,

Many thanks once again for sorting the EPROM for me.

The multimeter I have is a bit basic. It has been planning to upgrade for a while now, so this could be an ideal time. Have you any suggestions on a good upgrade?

Unfortunately I don't have an oscilloscope or logic analyser (but, again, open to any suggesstions you may have). I do have a couple of Raspberry Pis, and also a 4116/4164 RAM tester (which is Arduino based) - which I was thinking of using to test the RAM chips from the PET (the 4116).

Tim.
Hi Colin,

Thanks for the recommendation - I'll certainly look into that.

Cheers,
Tim.
retromit is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 7:13 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 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.