Commodore 8050 dual disk drive

[ScottishColin]

While I'm waiting so what if anything I can do with my printer, I'll switch to my 8050 disk drives.

Schematics here:

http://www.zimmers.net/anonftp/pub/c...schematics.pdf

I have power and will replace the existing sockets and see if I can get it not giving me a flashing error.

However, an inspection of the motherboard gives me the attached area which I think needs addressing.

The affected items are CR5 and CR6 which according to page 7 of the PDF are "diode IN5402 3A/200V". Is there any way of testing them before I go ordering? And is it worth replacing C64 and C66 while I'm there (P7, Ceramic Capacitor Axial .1mF"?

Thanks.

Colin.

[ortek_service]

I hadn't realised you also had a faulty disk-drive - Presumably one you got with your latest 4032 PET + Printer purchase - And a bit unlucky that none of these worked!

I recall seeing two disk drives in a recent photo you posted of your current Commodore (PET's) collection. So is the other (Presumably working) Disk Drive the same 8050 model? (And therefore may be useful for diagnosing any faults with more expensive, socketed IC's)

Regarding the 1N5402 diodes, they are fairly-easy to check using the 'Diode-test' range on a DMM - They should read around 0.5 - 1.0V when 'forward-biased' and open-circuit when 'reverse-biased' (Which can also / be better measured on a standard high resistance range).
Although there may be some effects of surrounding circuitry, so might need to de-solder one end to isolate it, to measure these properly and ensure they aren't actually measuring incorrectly themselves.
Alternatively, you could just measure the DC-voltage at the cathodes, with the supply on (Or use your 'scope to look at weaveforms etc, to make sure they are rectifying correctly - Which would save having to remove these / do 'cold' resistance checks on these.


If you do need to replace these, then just about any 1N540x diode should be OK as they are all 3A (Just different reverse-voltage ratings from 100V to 1000V, with not much impact on the the spec's. So if you do already have any of these (or other 3A rectifier diodes) / you find a good deal on other 1N540x ones, then should be OK to use these.
They are usually quite cheap (I saw 1N540x ones being sold in £1 bags for 20? at a Radio Rally on Sunday and would have bought them if I hadn't already got a few / 6A ones, I bought ages OK for fixing CB PSU's etc. Although I did buy a bag of 20off rather 'faster' UF5401's for use in high-frequency switching converter PSU's that are now the norm), so probably worth having a few extra for spares.

It's unlikely for 100nF Ceramic capacitors to go short in 'Low-Voltage' use, if they are a good make. And going open-circuit probably wouldn't cause complete non-operation. So I doubt these would need changing. But they are such a common component, that it's not a bad idea to have some spares around, for replacing any physically damaged ones or for building various projects.

It doesn't sound like flashing lights is really a power-type fault - Is there a useful troubleshooting chart / table in a service manual etc for these?
That blackened PCB look around CR5 / CR6 area may just be due to these running a bit warm over a long period of time, rather than an excess-current fault at present. And they might have been better fitted with longer leads / on stand-offs, if there's the height space above these, so that air can flow better around these and they are not in thermal contact with the PCB. Although it looks like the copper tracking area has also been getting a bit warm, and so heating the PCB material.
Is there a fan fitted in this 8050 disk drive? - I known the VIC-20 / C64 1541 FDD had a tendency to run rather warm, with people adding fans etc. in these.

[TonyDuell]

If the disk drive gives a repeated number of flashes on the LEDs after power-on (keeps on doing it) it means the firmware has detected some problem (RAM failure, disk processor failure, etc). There is a table of the codes in the original service manual which I have somewhere.

As you probably know, the disk drive units contain a pair of 650x processors (8050 is a pair of 6502s), one handles the IEEE-488 interface, file handling, etc. The other does the disk data encoding/decoding (watch out, the firmware for that one is in a 6530...). The clock is inverted to one of them, meaning they access memory alternately. There's a shared buffer RAM area, 4K bytes I think.

That RAM is 2114s. And not too surprisingly it's a common cause of failures.

[ortek_service]

Taking a look at those schematics originally linked to, they seem to be only the 'Digital' (Plus the +5V and two +12V Power-regulators), that these 1N5402 diodes are on, and 'Analog' boards. And the unit's transformer etc. wiring to the 'Digital' (+Power-regulators) board is not shown.

However, I would assume that there is a centre-tapped transformer feeding the anodes of these two 1N5402 diodes, to form a 'push-pull' full-wave rectifier that shares the power between the two 'halves'
And the 3rd pin on the 3-pin connector to these, that goes to their combined-cathodes, is probably an output to a Power LED?

But if the +5V supply does measure OK, and there are no over-loads due to faulty IC's / capacitors on this (or input the the 5V regulator), then the diodes are probably OK and have just run rather-warm over the years with the amount of current on the 5V supply that runs through these into the input of the +5V linear-regulator IC

[TonyDuell]

I found the full service manual on-line, for example here :

http://www.primrosebank.net/computer...ice_manual.pdf

It contains the wiring for the mains transformer, the disk drive units (motors/heads/etc) and the list of the flashing LED error codes.

[ScottishColin]

I did - I don't mind that they don't work; it's all part of the fun for me.

I have a 3040 which works so I can donate some items from there if need be but the drives are different as is the motherboard but they do share some common components. Commodore made an impressively large range of incompatible drives in a very short space of time....

No fan in this drive unit. I'll check the diodoes/capacitors as below; thanks.

Colin.

Originally Posted by ortek_service

I hadn't realised you also had a faulty disk-drive - Presumably one you got with your latest 4032 PET + Printer purchase - And a bit unlucky that none of these worked!

I recall seeing two disk drives in a recent photo you posted of your current Commodore (PET's) collection. So is the other (Presumably working) Disk Drive the same 8050 model? (And therefore may be useful for diagnosing any faults with more expensive, socketed IC's)

Regarding the 1N5402 diodes, they are fairly-easy to check using the 'Diode-test' range on a DMM - They should read around 0.5 - 1.0V when 'forward-biased' and open-circuit when 'reverse-biased' (Which can also / be better measured on a standard high resistance range).
Although there may be some effects of surrounding circuitry, so might need to de-solder one end to isolate it, to measure these properly and ensure they aren't actually measuring incorrectly themselves.
Alternatively, you could just measure the DC-voltage at the cathodes, with the supply on (Or use your 'scope to look at weaveforms etc, to make sure they are rectifying correctly - Which would save having to remove these / do 'cold' resistance checks on these.


If you do need to replace these, then just about any 1N540x diode should be OK as they are all 3A (Just different reverse-voltage ratings from 100V to 1000V, with not much impact on the the spec's. So if you do already have any of these (or other 3A rectifier diodes) / you find a good deal on other 1N540x ones, then should be OK to use these.
They are usually quite cheap (I saw 1N540x ones being sold in £1 bags for 20? at a Radio Rally on Sunday and would have bought them if I hadn't already got a few / 6A ones, I bought ages OK for fixing CB PSU's etc. Although I did buy a bag of 20off rather 'faster' UF5401's for use in high-frequency switching converter PSU's that are now the norm), so probably worth having a few extra for spares.

It's unlikely for 100nF Ceramic capacitors to go short in 'Low-Voltage' use, if they are a good make. And going open-circuit probably wouldn't cause complete non-operation. So I doubt these would need changing. But they are such a common component, that it's not a bad idea to have some spares around, for replacing any physically damaged ones or for building various projects.

It doesn't sound like flashing lights is really a power-type fault - Is there a useful troubleshooting chart / table in a service manual etc for these?
That blackened PCB look around CR5 / CR6 area may just be due to these running a bit warm over a long period of time, rather than an excess-current fault at present. And they might have been better fitted with longer leads / on stand-offs, if there's the height space above these, so that air can flow better around these and they are not in thermal contact with the PCB. Although it looks like the copper tracking area has also been getting a bit warm, and so heating the PCB material.
Is there a fan fitted in this 8050 disk drive? - I known the VIC-20 / C64 1541 FDD had a tendency to run rather warm, with people adding fans etc. in these.

[ScottishColin]

Thanks. Mine flashed four times (which is impossible according to page 7 of the manual so I'm going to re-socket and start there after my last White-Socket experience in the 4032.

Another Commodore journey.

Colin.

Originally Posted by TonyDuell

I found the full service manual on-line, for example here :

http://www.primrosebank.net/computer...ice_manual.pdf

It contains the wiring for the mains transformer, the disk drive units (motors/heads/etc) and the list of the flashing LED error codes.

[ScottishColin]

OK - three sockets replaced (both the 6532s and one of the 6502s) and I'm now down to 1 flash which indicates a 6532 error.

I have two 6532s in the printer which I have swapped in(but no way of knowing if they work) but still the same so I guess I'm off to hunt some known good 6532s.

Colin.

[ScottishColin]

And back to 4 flashes after swapping over some chips into my 4032 to test them. The 6522 and both the 6502s work in the 4032 so I can rule them out.

The flashing documentation is spectacularly unclear. So I'm checking other things. UH1 failing is an indicator of 3 flashes. The manual says it's a 2364. My STAG won;t read a 2364 - is there anything compatible with a 2364 that I can set my Stag to in order to read the contents of the ROM?

Colin.

[SiriusHardware]

Can your Stag do the Motorola MCM68764? As shown below, this old 8K 24 pin EPROM is pin compatible with the 2364 and can be used as a replacement for one if needed.

If it's in the Stag's device list, select Motorola MCM68764, drop the 2364 into the Stag and read it that way.

[ScottishColin]

It can, but neither of them are readable.

Colin.

Originally Posted by SiriusHardware

Can your Stag do the Motorola MCM68764? As shown below, this old 8K 24 pin EPROM is pin compatible with the 2364 and can be used as a replacement for one if needed.

If it's in the Stag's device list, select Motorola MCM68764, drop the 2364 into the Stag and read it that way.

[SiriusHardware]

Sounds unlikely, as that flashing LED behaviour is a function of firmware - unless there is firmware somewhere else, did Tony say that one of the RIOT-like devices in the unit also has firmware in it?

When you say 'unreadable', what does the programmer actually read in when you try to read them. All FFs?

[ScottishColin]

"Load failed. Device missing or faulty". I've tried adding them both into new sockets to see if that helps but it doesn't.

Colin.

[SiriusHardware]

Ah - does your STAG have a facility to ignore / turn off the device ID feature?

If not, if you still have your Arduino Mega you could try reading them out with that. The original sketch you used to try to read PET 1's ROMs just needs a small change to read out 8K rather than 4K.

[ortek_service]

Alternatively, you could try to see if your programmer supports the (TMS)2564, which is also designed to be compatible with 2364 ROM's (that are unusual, in being 8KB in a 24pin package) - And the 2564 is listed as alternative to the 2364's in the (hand written - some in German!) Commodore 8050 / 8250 System Overview drawing, that is the 3rd page in that pdf on zimmers originally linked to: http://www.zimmers.net/anonftp/pub/c...schematics.pdf

The TMS2564 is in a 28pin package, but has a second Vcc pin(24) for compatibility, with 2364's: https://www.jrok.com/datasheet/TMS2564.pdf
Where it seems you just bend the top 2 pins on each side, up and are OK to leave nCS1 and nCS2 n.c. (Presumably they have internal pull-downs?), as at: https://www.mutant-caterpillar.co.uk...oducts_id=5247

Otherwise, you could try making an adapter to a more-standard 2764, with some stacked IC sockets and the odd pin-swap as most are the usual JEDEC standard.
http://mhv.bplaced.net/cbmroms/2364.htm
https://forums.atariage.com/topic/30...rd-2764-eprom/

It would seem that Commodore 'DOS' is held in these two 2364 ROM's, as the Service Manual states (But seem to have an extra F on end-addresses!)
UH1: $C000 - $DFFFF?
UL1: $E000 - $EFFFF? (Not sure if this is EFFF (So 2KB), or FFFF (So 4KB)?

Whilst the 'Controller' is in the 1K ROM of the 6530 'PIA' RRIOT
- But not clear which of the 6502 CPU's (which apparently have shared memory at different address on each one) these ROM's are all mapped into.

If the 6530 RRIOT (Which it seems has internal mask-programmed address decoding to map where ROM etc goes) is actually mapped into to of 64K Memory map, then that would probably be the firmware that runs first to test the hardware. So night imply that this 6530 is at least mostly-OK. But there were replacement boards once made / more info about repauring these drives: http://blog.tynemouthsoftware.co.uk/...lacements.html

Maybe (Commodore) DOS runs on the other 6502 (or split between both?) - The Service manual is very light on useful details like this, and I've not found that much on the 'net. With a Wikipedia page seemingly have the most general info: https://en.wikipedia.org/wiki/Commodore_8050

[ortek_service]

Reading up on the 3040 (Europe) / 2040 (USA), and the later 4040 successor, it seems they mostly had the same physically disc-format as later 1541 drive for the VIC-20/ C64 (Which it seems you could also get a Parallel IEEE-488 adaptor for to use these 'PET' drives) - Although they added an extra byte to a header that messed up write-compatibility between 1541 and 4040 etc.

And these used a fairly standard 48TPI Single-sided FDD mechanism (but limited to 35T due to drive-mechanism limitations on the 4040 / earlier, whereas later 1541 ones could in theory go to the full 40Tracks - Although not supported in their Commodore DOS version).

However, with the 8050 / 8250, they went for a very non-standard 100TPI (rather than the more usual 96TPI on 80T drives) 77T drives, that apparently are referred to as 'Quad' density - but only work with standard Double-density disks, not the special HD ones used with PC 1.2M drives). And the 8250 used Double-sided (compared to only using Single-sided ones in the 8050 and previous driives / some later ones like 1541).
Although I've read conflicting formatted capacities for the 8050 of 500KB per side or 1.05MB in Service Manual (Unless that's for both drives). With 8250 spec'd to be 2.12MB formatted.

So it does seem that if you want to be able to read a variety of disks, you do need 8000-series, as well as previous 4040/3040 ones - as not backward compatible,


It does look like the diodes (and capacitors) are probably OK, if the unit is powering-up OK and the boot-test firmware is running. Although it's possible to have a subtle fault with the power rails being a bit low / dipping under load, so not a bad idea to measure all with a DMM / check they are free of any fluctuations with a ;scope, in case there could be issues with these that might be upsetting the firmware from running correctly.

Originally Posted by ScottishColin

I did - I don't mind that they don't work; it's all part of the fun for me.

I have a 3040 which works so I can donate some items from there if need be but the drives are different as is the motherboard but they do share some common components. Commodore made an impressively large range of incompatible drives in a very short space of time....

No fan in this drive unit. I'll check the diodoes/capacitors as below; thanks.

Colin.

[TonyDuell]

The flashing LEDs are indeed controlled by the firmware (on the 'interface' processor) so in theory if that's corrupted anything could happen. This is the commodore DOS ROM set, a total of 16K bytes. (pair of 2364s) at the top of that processor's memory map.

The 6530 firmware is for the 'controller' processor. If that's missing or faulty, the interface processor/firmware will still run and give a flash code on the LEDs.

The 2 processors have their own memory space each. They share the 4K buffer RAM (8 off 2114s). The other devices -- the ROMs, the 6532s, the other I/O can be accessed by only one of the processors.

And yes, they're 100tpi. 77 cylinders. And of course GCR encoding. So good luck reading the disks on anything else!

[ortek_service]

Thanks for the explanation.

It's maybe a bit unexpected that the DOS on the 'Interface' processor does the diagnostics, rather than the much-smaller 'Controller' ROM in the 6530 RRIOT. So that could still be an issue, even if the diagnostic test (In the Upper 2364 DOS ROM) seems to be running so that ROM is at least mostly-working.


I'd also discovered there's a 4th 2KB 'Decoder' ROM, but it seems this maybe just a translating look-up table for the GCR encoding.


Yes, 100TPI alignment disks must be even more difficult to obtain than more-conventional 96TPI etc ones these days!

Although I presume 100TPI was used on systems other than Commodore, for several drive manufacturers to make these, but it seems it was a rather failed-format and most went for 96TPI that allowed much-more compatibility (usually OK for reading disk written with 'full-width' heads at least) with original 48TPI disks.
But I presume Commodore didn't adopt 96TPI until very much later with C64 / C128 drives (1571?) after the 1541.

[SiriusHardware]

Thanks for that info, Tony - with the 2364s fitted the 'error flash' system seems to be working after a fashion, which makes it seem unlikely that the ROMs are so faulty as to be unreadable.

Motorola 68764s are such old devices that it would surprise me if they had a device ID feature like that found in more modern EPROMs so I'm not sure what it is about the 2364s which the STAG programmer is not liking. They should be compatible in pure read mode - I've heard of people using the 68764s to substitute for similar ROMs in VIC20s I think.

[TonyDuell]

The LEDs are controlled by ports accessible only by the 'Interface' processor so that has to be the one to run the diagnostics. I think there's some kind of test in the 'Controller' firmware, but the pass/fail is reported via the 'Interface' processor.

The 2K ROM is indeed the GCR translation table and is not in the memory map of either processor.

Never seen a 100tpi alignment disk (although they did exist). Notice that the Commodore service manual says nothing about replacing heads, stepper motors, or doing the radial alignment. You were expected to replace the drive mechanism if any of that needed doing. AFAIK the 1571 was 48tpi (although with an MFM controller chip as well as the GCR stuff), there never was a 100tpi drive for the C64 series.