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Bad CHIP - CBM 8050 drive - 901887

Tdillon

Tdillon

Member
Joined
Jan 15, 2024
Messages
49
Location
Colborne, Ontario Canada
I had 3 flashing lights on a CBM 8050 drive. After replacing the 901887-01 chip, it worked properly. But now I need a 901887 chip.
There are some available on ebay, but they aren't programmed and I have no way to do program them.
Is there a source for a ready to use 901887 chip?
Or is there a means to flash the chip if it was previously used for something else? If so, who can flash it? (bin is available on zimmer site).
 
I am a little confused.

There is a 901887-01.bin file on Zimmers.

I can't see a 901887 image (no -01) on Zimmers.

If you replaced it, and the 8050 works, why do you need another one (unless you borrowed this from a friend or you need a spare)?

To my knowledge, the 2364 is a mask programmed ROM - so the contents is fixed. The 901887-01 refers to the PROM content. If the PROM is marked as a 901887-01 it should contain the correct image.

If you need to program your own device (using the 901887-01.bin image from Zimmers) you will need a 2364 to 2764 adapter, and then you can program the .bin image into a standard EPROM.

If you can find a 901887-01 ROM on eBay (or wherever), it should contain the correct image already (unless it is duff).

Dave
 
I interpret this as meaning that he has substituted the original 901887-01 ROM with an EPROM + Adaptor, but is now seeking an actual replacement ROM.

The problem is that these devices weren't programmable, the masked-ROM program code was 'baked in' at the point of manufacture of the chip so there's no such thing as an unprogrammed, programmable 901887 chip. You can only hope to find an original 901887-01 ROM with the correct code already built in and hope that, unlike your original chip, it is OK.
 
daver2 said:
I am a little confused.

There is a 901887-01.bin file on Zimmers.

I can't see a 901887 image (no -01) on Zimmers.

If you replaced it, and the 8050 works, why do you need another one (unless you borrowed this from a friend or you need a spare)?

To my knowledge, the 2364 is a mask programmed ROM - so the contents is fixed. The 901887-01 refers to the PROM content. If the PROM is marked as a 901887-01 it should contain the correct image.

If you need to program your own device (using the 901887-01.bin image from Zimmers) you will need a 2364 to 2764 adapter, and then you can program the .bin image into a standard EPROM.

If you can find a 901887-01 ROM on eBay (or wherever), it should contain the correct image already (unless it is duff).

Dave
Click to expand...
901887-01. I removed a good one from working 8050, which must be put back.
 
Ok,

So all you need to do is either purchase a replacement 901887-01 ROM from a vendor (this will have the correct code already in it), or use a blank 2764 EPROM, burn the correct Zimmers image into that and use an adapter.

Your choice...

Dave
 
Ruud said:
There is one on Ebay right now. And otherwise contact me, mail address is on my site.
Click to expand...
Actually, that TVsat-electronica company selling those in Poland.............I have bought chips from them in the past and all very good. That chip will likely be fine for the OP.
 
There is something not quite right about this eBay advert.

It mentions both a 901887-01 and a 901885-04.

The 901887-01 is a 24 pin ROM whereas the 901885-04 is a 40 pin RRIOT.

It may be a stock photograph they have used - or are totally confused by the Commodore terminology.

Perhaps check with the seller exactly what they are selling before buying?

Dave
 
daver2 said:
There is something not quite right about this eBay advert.

It mentions both a 901887-01 and a 901885-04.

The 901887-01 is a 24 pin ROM whereas the 901885-04 is a 40 pin RRIOT.

It may be a stock photograph they have used - or are totally confused by the Commodore terminology.

Perhaps check with the seller exactly what they are selling before buying?

Dave
Click to expand...
That sounds sensible.

They have amazingly good feedback though, somebody complained about shipping time and another about invoices, there is no mention at all of fake parts.
 
I have Commodore ROMs. I could back up one of them - or send you one if necessary. I would need to check the part number.
 
daver2 said:
Ok,

So all you need to do is either purchase a replacement 901887-01 ROM from a vendor (this will have the correct code already in it), or use a blank 2764 EPROM, burn the correct Zimmers image into that and use an adapter.

Your choice...

Dave
Click to expand...
Thank you. I found one online to purchase, and successfully replaced it. There are no error lights, but drive 0 doesn't read. I suspect it is out of alignment, but I am not going to repair it - just selling it as it is with one side working properly. I have two of them like that.
 
Tdillon said:
Thank you. I found one online to purchase, and successfully replaced it. There are no error lights, but drive 0 doesn't read. I suspect it is out of alignment, but I am not going to repair it - just selling it as it is with one side working properly. I have two of them like that.
Click to expand...
Try formatting an erased disk (ie use a magnet to wipe it) and see if it will read/write that disk in drive 0 but not in drive 1. If thats the case its out of alignment, if it won't format a blank disk, its not alignment.
 
Gary C said:
Try formatting an erased disk (ie use a magnet to wipe it) and see if it will read/write that disk in drive 0 but not in drive 1. If thats the case its out of alignment, if it won't format a blank disk, its not alignment.
Click to expand...
If I understand, you are saying to try drive 0 to format a new/ blank disk and see if it reads the newly formatted disk. If drive 0 does read it, then it's out of alignment (therefore drive 1 won't read it because it's formatted with misalignment). But if it won't see the blank disk and format, then it's not alignment.
Which means, if a disk drive (head) is out of alignment, it can still always read a blank disk and format it. Is this correct?
 
Basically yes

You suspect drive 0 is not reading because its not of the same alignment as drive 1 (which we can assume is aligned correctly, normally by being able to read a commercially produced disk or from another machine), so if drive 0 can write then read from a blank disk, that would prove it (especially if that disk would then not work in drive 1)

The disk should be blank (ie not preformatted) because any previously recorded tracks could conceivably cause errors (even though the heads should trim the new tracks) and its easy to do with a magnet using in a swirling pattern around the disk.

It would help your sale if you could prove the drive works and really only needs aligning.
 
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