Commodore 8050 Disk Drive Issue - UK Vintage Radio Repair and Restoration Discussion Forum

centrespot · 20th Dec 2024, 7:18 pm

Hi All

My 8050 Disk Drive unit is responding to the PET commands but isn't working properly.

When I send the command to format a disk : header "test",d0,i11 the drive responds by rotating the disk and the head moves backwards until it hits the stop, the head motor keeps trying to rotate making a louder noise for about 2 seconds then stops, the disk continues rotating indefinitely so I have to power it off.

What would be the likely issues ?

Thanks in advance.

SiriusHardware · 21st Dec 2024, 12:24 am

I don't know these (others here know them better and / or actually have them) but I would expect there would be a head 'home' switch or sensor which gets operated when the head has 'seeked' to the 'home' position. It sounds like that is not happening so the motor keeps on trying to drive the head in the same direction.

Eventually the firmware realises it has taken too long for the head to 'seek' to the home position and it stops trying to drive the head.

That's my theory anyway. Do we have the diagrams for these?

TonyDuell · 21st Dec 2024, 4:22 am

I do have the service manual for the 8050/8250 drives

There is no track0 sensor (or index sensor for that matter) in these drives. It's supposed to bang the head into the end stop (!). No I don't like it either.

My guess as to the fault is that the 'interface processor' in the drive unit -- the one that talks to the GPIB port, etc is not getting the right response from the controller processor (the one that actually handles the disk data). It could be a lot of things, but they communicate via a shared 4K area of RAM made up of 2114s. As is well-known they are not the most reliable of chips and while they are checked by the power-on tests it doesn't pick up all possible faults.

SiriusHardware · 21st Dec 2024, 10:47 am

I know Tony has a paper service manual for these, which is a good start.

There is also a service manual - probably the same one - here, for anyone else who wants to sing along.

http://www.primrosebank.net/computers/pet/documents/8050_8250_service_manual.pdf

To begin with, measure all supply voltages to make sure they are all present and correct.

If the supplies are OK and it's nothing to do with the head trying and failing to home and the disc does keep spinning, and if the RAMs are OK, then maybe the next thing would be to look at the output from the head amplifier / squarer circuit?

ScottishColin · 21st Dec 2024, 5:38 pm

I have a working 8050 but it's tucked away right now along with the PETs and it won't be coming out this side of Christmas I'm afraid.

So I'm happy to help when I can but it won't be for a week or so.

In the meantime, this thread may or may not help....

https://www.vintage-radio.net/forum/showthread.php?t=203300

Colin.

centrespot · 24th Dec 2024, 3:11 pm

I bought some 96tpi disks just in case the ones I tried were the issue but still the same when I try the new disks.

I have NOP tested the two 6502's and put the 6522 chip in the PET which works fine, I will socket the RAM chips and test them next.

ScottishColin · 24th Dec 2024, 8:58 pm

It might seem a bit of a faff, but it would be good if you could type in and run the program on p184 (CHAPTER 8 - A GPIB Diagnostic Test) of this book:

http://primrosebank.net/computers/pet/documents/PET_and_the_IEEE488_Bus_text.pdf

It'll test the IEEE port and the chips that control it and then we can rule it out of any further questions.

Colin.

SiriusHardware · 25th Dec 2024, 11:55 am

CS did mention in his recent 'PET Monitor' thread that he has a commercially made IEEE-488 test rig for his PETs, although experience has admittedly taught us that different tests / testers can sometimes disagree.

ScottishColin · 25th Dec 2024, 2:59 pm

My last PET taught me that you can't test too often, or with too many devices...

ScottishColin · 28th Dec 2024, 4:18 pm

I'm getting to the stage where I can sneak the 8050 out. Which PET model is it so I can have a like-for-like setup?

centrespot · 29th Dec 2024, 11:50 am

Quote:

Originally Posted by ScottishColin

I'm getting to the stage where I can sneak the 8050 out. Which PET model is it so I can have a like-for-like setup?

Hi Colin

It's the PET 8096/8032

I've de-soldered and tested the RAM, I only had 6 sockets so I'm waiting for more to arrive before I can put it back together.

ScottishColin · 29th Dec 2024, 2:43 pm

Right. I'll get out my 8032 and the 8050, connect them and check that they're working together.

SiriusHardware · 29th Dec 2024, 4:08 pm

Centrespot,

Sorry to sound like a stuck record but is the 8050 (not) working in exactly the same fashion when connected to your other PET? Just to be sure this is definitely a drive fault and not a computer fault.

ScottishColin · 29th Dec 2024, 6:28 pm

OK - 8032 out and connected to the 8050. Tested a HEADER command on both drives fine.

Interestingly, I have another 8032 that would not connect to the disk drive unit at all, even though it passes the IEEETEST program in post 7.....

Colin.

centrespot · 29th Dec 2024, 6:33 pm

Quote:

Originally Posted by SiriusHardware

Centrespot,

Sorry to sound like a stuck record but is the 8050 (not) working in exactly the same fashion when connected to your other PET? Just to be sure this is definitely a drive fault and not a computer fault.

Correct, I tried it on a 4032 as well.

_Clint_ · 30th Dec 2024, 2:22 pm

I have a few of these drives and sounds like a read error for sure, but obviously there are many things than can cause the result.

I dont mess about with IEEE488 testers any more I have one of these pet SD things and just plug it in and see if it works - if it works i know the port is ok.

https://www.ebay.co.uk/itm/387256862564

TonyDuell · 30th Dec 2024, 4:08 pm

I seem to remember there are some low-level commands on the 8050 that let you read/write the interface processor's memory over the IEEE-488 bus, things like that.

There are no BASIC4 keywords for these, you have to send the correct string to secondary address 15. And read the results back.

If those work it means the IEEE-488 interface, interface processorm, ROMs, etc are essentally working correctly. Problem is likely to be on the disk controller processor, the 6530, 6522 and all the TTL in the data decoder.

A good reference on said low-level commands is 'Programming the PET / CBM' by Raeto West. It seems to be available to download.

ScottishColin · 30th Dec 2024, 4:35 pm

If you attempt to perform the HEADER command, after it fails (assuming the PET isn't locked), type the following and let us know what it says:

PRINT DS$

After a successful HEADER on my 8032/8050, I get the following response:

00, ok,00,00

If I perform a DIRECTORY on a drive with no disk in it, I get

74,drive not ready,00,00

The error numbers are listed from P 50 in the following manual:

https://www.zimmers.net/anonftp/pub/cbm/manuals/drives/CBM-D...D9090-D9060-8250-8050-4040-2031.pdf

Colin.

centrespot · 30th Dec 2024, 8:40 pm

Well this is annoying, I fitted the tested RAM in the new sockets and now I just get the three LED's lighting up and staying on. No noise or movement from the drives.

SiriusHardware · 30th Dec 2024, 9:41 pm

I'm afraid Sherlock Holmes would say that this is probably a case of cause and effect. It was behaving one way, you did something and now it's behaving differently.

It's not impossible for a new independent failure to have occurred while you were in the middle of all that rework but it is much more likely that you inadvertently disturbed or disconnected something or perhaps lifted a track or damaged a through-hole via while socketing the RAMs. Unfortunately, you need to rule all of those things out before you can proceed.

I would also just check that you haven't accidentally folded a PIN over on one of the RAMs when you last inserted them - as I often say, I have been putting DIP parts in sockets for at least 50 years and even I still manage to do that sometimes.

20th Dec 2024, 7:18 pm	#1
centrespot Hexode Join Date: Jan 2021 Location: Eardisley, Herefordshire, UK Posts: 314	Commodore 8050 Disk Drive Issue Hi All My 8050 Disk Drive unit is responding to the PET commands but isn't working properly. When I send the command to format a disk : header "test",d0,i11 the drive responds by rotating the disk and the head moves backwards until it hits the stop, the head motor keeps trying to rotate making a louder noise for about 2 seconds then stops, the disk continues rotating indefinitely so I have to power it off. What would be the likely issues ? Thanks in advance.

21st Dec 2024, 12:24 am	#2
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 13,785	Re: Commodore 8050 Disk Drive Issue I don't know these (others here know them better and / or actually have them) but I would expect there would be a head 'home' switch or sensor which gets operated when the head has 'seeked' to the 'home' position. It sounds like that is not happening so the motor keeps on trying to drive the head in the same direction. Eventually the firmware realises it has taken too long for the head to 'seek' to the home position and it stops trying to drive the head. That's my theory anyway. Do we have the diagrams for these?

21st Dec 2024, 4:22 am	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 6,063	Re: Commodore 8050 Disk Drive Issue I do have the service manual for the 8050/8250 drives There is no track0 sensor (or index sensor for that matter) in these drives. It's supposed to bang the head into the end stop (!). No I don't like it either. My guess as to the fault is that the 'interface processor' in the drive unit -- the one that talks to the GPIB port, etc is not getting the right response from the controller processor (the one that actually handles the disk data). It could be a lot of things, but they communicate via a shared 4K area of RAM made up of 2114s. As is well-known they are not the most reliable of chips and while they are checked by the power-on tests it doesn't pick up all possible faults.

21st Dec 2024, 10:47 am	#4
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 13,785	Re: Commodore 8050 Disk Drive Issue I know Tony has a paper service manual for these, which is a good start. There is also a service manual - probably the same one - here, for anyone else who wants to sing along. http://www.primrosebank.net/computers/pet/documents/8050_8250_service_manual.pdf To begin with, measure all supply voltages to make sure they are all present and correct. If the supplies are OK and it's nothing to do with the head trying and failing to home and the disc does keep spinning, and if the RAMs are OK, then maybe the next thing would be to look at the output from the head amplifier / squarer circuit? Last edited by SiriusHardware; 21st Dec 2024 at 10:55 am.

21st Dec 2024, 5:38 pm	#5
ScottishColin Nonode Join Date: May 2012 Location: Perth, Scotland Posts: 2,436	Re: Commodore 8050 Disk Drive Issue I have a working 8050 but it's tucked away right now along with the PETs and it won't be coming out this side of Christmas I'm afraid. So I'm happy to help when I can but it won't be for a week or so. In the meantime, this thread may or may not help.... https://www.vintage-radio.net/forum/showthread.php?t=203300 Colin.

24th Dec 2024, 3:11 pm	#6
centrespot Hexode Join Date: Jan 2021 Location: Eardisley, Herefordshire, UK Posts: 314	Re: Commodore 8050 Disk Drive Issue I bought some 96tpi disks just in case the ones I tried were the issue but still the same when I try the new disks. I have NOP tested the two 6502's and put the 6522 chip in the PET which works fine, I will socket the RAM chips and test them next.

24th Dec 2024, 8:58 pm	#7
ScottishColin Nonode Join Date: May 2012 Location: Perth, Scotland Posts: 2,436	Re: Commodore 8050 Disk Drive Issue It might seem a bit of a faff, but it would be good if you could type in and run the program on p184 (CHAPTER 8 - A GPIB Diagnostic Test) of this book: http://primrosebank.net/computers/pet/documents/PET_and_the_IEEE488_Bus_text.pdf It'll test the IEEE port and the chips that control it and then we can rule it out of any further questions. Colin.

25th Dec 2024, 11:55 am	#8
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 13,785	Re: Commodore 8050 Disk Drive Issue CS did mention in his recent 'PET Monitor' thread that he has a commercially made IEEE-488 test rig for his PETs, although experience has admittedly taught us that different tests / testers can sometimes disagree.

25th Dec 2024, 2:59 pm	#9
ScottishColin Nonode Join Date: May 2012 Location: Perth, Scotland Posts: 2,436	Re: Commodore 8050 Disk Drive Issue My last PET taught me that you can't test too often, or with too many devices...

28th Dec 2024, 4:18 pm	#10
ScottishColin Nonode Join Date: May 2012 Location: Perth, Scotland Posts: 2,436	Re: Commodore 8050 Disk Drive Issue I'm getting to the stage where I can sneak the 8050 out. Which PET model is it so I can have a like-for-like setup?

29th Dec 2024, 2:43 pm	#12
ScottishColin Nonode Join Date: May 2012 Location: Perth, Scotland Posts: 2,436	Re: Commodore 8050 Disk Drive Issue Right. I'll get out my 8032 and the 8050, connect them and check that they're working together.

29th Dec 2024, 4:08 pm	#13
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 13,785	Re: Commodore 8050 Disk Drive Issue Centrespot, Sorry to sound like a stuck record but is the 8050 (not) working in exactly the same fashion when connected to your other PET? Just to be sure this is definitely a drive fault and not a computer fault.

29th Dec 2024, 6:28 pm	#14
ScottishColin Nonode Join Date: May 2012 Location: Perth, Scotland Posts: 2,436	Re: Commodore 8050 Disk Drive Issue OK - 8032 out and connected to the 8050. Tested a HEADER command on both drives fine. Interestingly, I have another 8032 that would not connect to the disk drive unit at all, even though it passes the IEEETEST program in post 7..... Colin.

30th Dec 2024, 2:22 pm	#16
_Clint_ Pentode Join Date: Mar 2011 Location: Sevenoaks, Kent, UK. Posts: 107	Re: Commodore 8050 Disk Drive Issue I have a few of these drives and sounds like a read error for sure, but obviously there are many things than can cause the result. I dont mess about with IEEE488 testers any more I have one of these pet SD things and just plug it in and see if it works - if it works i know the port is ok. https://www.ebay.co.uk/itm/387256862564 __________________ If it sparks, it was either meant to spark, or something is wrong, very very wrong.

30th Dec 2024, 4:08 pm	#17
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 6,063	Re: Commodore 8050 Disk Drive Issue I seem to remember there are some low-level commands on the 8050 that let you read/write the interface processor's memory over the IEEE-488 bus, things like that. There are no BASIC4 keywords for these, you have to send the correct string to secondary address 15. And read the results back. If those work it means the IEEE-488 interface, interface processorm, ROMs, etc are essentally working correctly. Problem is likely to be on the disk controller processor, the 6530, 6522 and all the TTL in the data decoder. A good reference on said low-level commands is 'Programming the PET / CBM' by Raeto West. It seems to be available to download.

30th Dec 2024, 4:35 pm	#18
ScottishColin Nonode Join Date: May 2012 Location: Perth, Scotland Posts: 2,436	Re: Commodore 8050 Disk Drive Issue If you attempt to perform the HEADER command, after it fails (assuming the PET isn't locked), type the following and let us know what it says: PRINT DS$ After a successful HEADER on my 8032/8050, I get the following response: 00, ok,00,00 If I perform a DIRECTORY on a drive with no disk in it, I get 74,drive not ready,00,00 The error numbers are listed from P 50 in the following manual: https://www.zimmers.net/anonftp/pub/cbm/manuals/drives/CBM-D...D9090-D9060-8250-8050-4040-2031.pdf Colin.

30th Dec 2024, 8:40 pm	#19
centrespot Hexode Join Date: Jan 2021 Location: Eardisley, Herefordshire, UK Posts: 314	Re: Commodore 8050 Disk Drive Issue Well this is annoying, I fitted the tested RAM in the new sockets and now I just get the three LED's lighting up and staying on. No noise or movement from the drives.

30th Dec 2024, 9:41 pm	#20
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 13,785	Re: Commodore 8050 Disk Drive Issue I'm afraid Sherlock Holmes would say that this is probably a case of cause and effect. It was behaving one way, you did something and now it's behaving differently. It's not impossible for a new independent failure to have occurred while you were in the middle of all that rework but it is much more likely that you inadvertently disturbed or disconnected something or perhaps lifted a track or damaged a through-hole via while socketing the RAMs. Unfortunately, you need to rule all of those things out before you can proceed. I would also just check that you haven't accidentally folded a PIN over on one of the RAMs when you last inserted them - as I often say, I have been putting DIP parts in sockets for at least 50 years and even I still manage to do that sometimes.