| Posted By
rossi
on 2023-08-10
12:33:43
|  1551 diagnostic / 1551test.prg / repair possible?
Hi together,
since this is my first post to this forum, I would like to take the time to introduce myself first, please apologize therefore if this post is a little bit more lengthy and not straight into the topic. I'm in my early 50s and live in Germany, Bavaria to be a little bit more specific. I nowadays work in the rail industry, being responsible for onboard WIFI services. As a kid I used to own a C16 expanded to 64k (done with the help go my uncle, due to my - still - bad soldering skills as a software guy) with a 1551 drive. Unfortunately I had to sell those when I upgraded to an Amiga 500 in 1987, which I again had to sell to chip in my own part to a high school exchange year in the states. A couple years ago I obtained a Plus/4 mostly due to nostalgia and recently finally managed to actually start to tinker with it again. I must admit, my memory is so bad, that I had to read the manuals again for refreshing my knowledge of the basic instructions
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Posted By
rossi
on 2023-08-10
12:34:48
| Re: 1551 diagnostic / 1551test.prg / repair possible?
(cont.)
I must admit, my memory is so bad, that I had to read the manuals again for refreshing my knowledge of the basic instructions
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Posted By
rossi
on 2023-08-10
12:36:18
| Re: 1551 diagnostic / 1551test.prg / repair possible?
(sorry for the third try)
Hi together,
since this is my first post to this forum, I would like to take the time to introduce myself first, please apologize therefore if this post is a little bit more lengthy and not straight into the topic. I'm in my early 50s and live in Germany, Bavaria to be a little bit more specific. I nowadays work in the rail industry, being responsible for onboard WIFI services. As a kid I used to own a C16 expanded to 64k (done with the help go my uncle, due to my - still - bad soldering skills as a software guy) with a 1551 drive. Unfortunately I had to sell those when I upgraded to an Amiga 500 in 1987, which I again had to sell to chip in my own part to a high school exchange year in the states. A couple years ago I obtained a Plus/4 mostly due to nostalgia and recently finally managed to actually start to tinker with it again. I must admit, my memory is so bad, that I had to read the manuals again for refreshing my knowledge of the basic instructions. My nickname in those times had been rossi, thus the "username" for this posting.
Now getting finally to my current topic, I just managed to obtain a 1551 for an outrageous amount of money, which according to the seller had been never used an still came in the original packaging. The drive powers on and the error led is off. However when I try to read the directory of the included test disk I get the following error: "27 READ ERROR 18 0". To verify that it's not the disk I bought another test disk and a NOS package of blank disks. However I get the same error with the second disk. The leads me to suspect the culprit might be the drive and not the disk.
After a some research I stumbled upon the 1551TEST.PRG from Rob Clarke. Thanks at this point to Rob for writing and sharing this tool. However I didn't manage to find any documentation for the tool.
I have additionally an SD2IEC on address 9, which I use to actually run the tool, as I have no way to transfer the tool to a cassette.
To further diagnose the issue I now try to understand the output of the tool. I get the following results from the different tests (I only list the faulty ones):
1. Test: Default register values at $FEC0: Port A (R0): 85 Bad Stable
9. Test: Internal drive pull-ups: Port C (R2): 192 Ok Unstable
The test program tries to read from the drive and exits with "21 READ ERROR 18 0".
As I'm totally way over my head here, I would kindly ask for help to figure out what's wrong and how to potentially fix, if possible.
Btw, theoretically I could still return the drive to the seller until August 21.
Thanks in advance for any ideas!
Cheers,
Marcus aka rossi
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Posted By
BSZ
on 2023-08-10
16:22:38
| Re: 1551 diagnostic / 1551test.prg / repair possible?
I'm not sure what you've exactly tried so far, but a few things come to mind.
If the 1551 drive has unit number 8, the base address of the paddle is $FEFx. Specifically, $FEE0..$FEFF, this is the range over which the 8 registers (6 used, 2 unused) of the TIA are repeated 4 times. But the machine's kernal uses the $FEF0..$FEF5 addresses. The address range of a drive with unit number 9 is $FEC0..$FEDF, of which the addresses used are $FEC0..$FEC5. (Is the test testing a non-existent drive's paddle?)
But... The error "21 READ ERROR 18 0" is provided by the drive, so if you see this, the communication with the drive is OK. Probably the paddle is fine. This error code means that it has failed to read the 18:0 sector because it cannot find a synchronizing sequence. (The 18:0 is the BAM of the disk, the drive always start with this for a new disk.)
This error occurs if the disk is missing or badly formatted. If the disk works fine in another drive, there is a problem with this 1551 drive. Unfortunately, this is often caused by mechanical failure; the 1551 has the "infamous" D500 mechanism, which has a head that tends to fail. (This is easy to check with a multimeter, but if you haven't done it before, it may not be a good idea to learn on this.  )
If you don't have a good disk / drive handy, try a disk format:
HEADER "NAME",IXX,D0
If the format does success, the drive may be fine. If it fails, the error message may be interesting.
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Posted By
rossi
on 2023-08-11
05:31:17
| Re: 1551 diagnostic / 1551test.prg / repair possible?
Thanks for the insights, I already tried to format multiple new disks, format fails with the error bad disk respectively 74, drive not ready, 01, 01 ... I guess then I have to look for a new head / mechanic ...
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Posted By
SVS
on 2023-08-11
15:18:03
 | Re: 1551 diagnostic / 1551test.prg / repair possible?
Hi,
maybe I'm banal, but from my experience over the 1551s, you should unconnect the SD2IEC and tried again. The correct sequence is:
- Switch off the Plus4 and the drivers.
- Wait for a while (say 10 secs)
- Switch on the 1551
- Switch on the Plus4
Let me know.
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Posted By
BSZ
on 2023-08-11
15:30:24
| Re: 1551 diagnostic / 1551test.prg / repair possible?
Before looking for a new mechanic, it would be a good idea to check if that is the problem.  Is the disk spinning anyway? In this mechanism, the disc is driven by a flat belt. It is a nearly 40-year-old equipment, and the flat belt is partly rubber. This can also cause such errors.
If the head turns out to be at fault, look for full mechanics, not just head. Adjusting the head is very difficult without the right instruments.
@SVS: SD2IEC does not cause any bugs in this way, that is not the problem here, IMHO.
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Posted By
rossi
on 2023-08-12
13:30:16
| Re: 1551 diagnostic / 1551test.prg / repair possible?
Hi again,
first thanks for the additional insights. All relevant tests have been done with the SD2IEC disconnected, even though the SD2IEC is permanently configured to address 9 to avoid conflicts. The only test run, with SD2IEC connected was the 1551test.prg run, as I have no other means to get the software on the hardware.
The disks seem to be spinning, at least judging by the horrendous noise, which I don't remember that loud from the 80s ...
Tomorrow I'll open the drive and see further ...
Cheers,
Rossi
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