Posted By
Xerox
on 2024-02-07
15:03:44
|  Weird Floppy 1551 Problem
I'm facing a weird problem with my Floppy 1551 and I think the problem is within the pedal board.
When I do a Print DS$ I get back a string from the floppy, however bit 5 is locked.
This can be proven by subtracting 32 from the ASCII string (see pictures).
You can see a green wire that has been soldered to exatly that bit. I'm not sure why this was done as it wasn't the standard for these paddle boards.
Anyone out there, who does have an idea on what component I should swap?
I already unsoldered the green wire, but that rendered the device completey broken - not even answering to DS$ anymore.
The CPU in the floppy seems fine as it is answering.
Should I try to change the T6523 just for the sake of it?
Here come the PICs:
  
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Posted By
SukkoPera
on 2024-02-07
15:18:34
| Re: Weird Floppy 1551 Problem
Yes, if you have another drive try swapping the 6523. But the problem might also be inside the drive or in the cable, I will take a look at the schematics.
Where is the other end of the green wire connected? It's not clear from the picture.
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Posted By
SVS
on 2024-02-07
15:17:49
 | Re: Weird Floppy 1551 Problem
Hi,
the 1551 paddle is a critical component. You should unplug the T6523 (or the entire paddle) and connect it to a known working 1551. Obviously don't insert a new T6523 to your paddle (that could be itself faulty). This is just to know what is burnt.
In my experience this is a problematic chip/circuit, I have had (in the Gold Hera) a lot of problems with it. People used to change the entire paddle instead of struggling to find what the faulty object was.
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Posted By
crock
on 2024-02-07
16:10:49
 | Re: Weird Floppy 1551 Problem
If I were to guess, someone has tried to patch a broken track. Test the continuity from pin 16 on the edge connector to pin 26 on the 6523T socket. I assume that is where the wire was going?
You could try this:
http://inchocks.co.uk/commodore/1551/1551test.prg
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Posted By
Xerox
on 2024-02-08
01:30:05
| Re: Weird Floppy 1551 Problem
Thanks for first recommendations! I tested continuity on the given connection and it is ok.
I do not have another 1551 to test and T6523 are hard to get these days.
Anyone has some on stock?
I've never seen people sell a paddle board though, which would be even better to try...
I'm based in Germany/Europe...
Or could these one's work?
https://www.mutant-caterpillar.co.uk/shop/product_info.php?products_id=4311&osCsid=69dl7oiskd8qaasc1lkltjhoi3
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Posted By
SukkoPera
on 2024-02-08
04:05:16
| Re: Weird Floppy 1551 Problem
Unfortunately that is a replacement for the other chip.
But you can try this!
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Posted By
crock
on 2024-02-08
04:42:13
| Re: Weird Floppy 1551 Problem
@Xerox can you confirm where that green wire connects from and too? Is it in parallel with the track on the PCB?
There is no current replacement for the 6523T, it was on the list of @MCes to tackle but I'm not sure if he progressed it since we last spoke.
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Posted By
SukkoPera
on 2024-02-08
04:55:44
| Re: Weird Floppy 1551 Problem
The edge connector pin the wire connects to is definitely D5.
The 6523T is just a 6523 with reduced pin count, so it should just be sufficient to make a new PCB for the project I linked above removing the "extra" pins.
Another interesting possibility is in the last few posts here. Unfortunately these German guys often prefer to keep things sitting in their drawers :(.
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Posted By
crock
on 2024-02-08
11:09:30
| Re: Weird Floppy 1551 Problem
@SukkoPera Right, but I'm also interested if it's going to Pin 26 of the 6523T, which is also D5, but I can't imagine it would be going anywhere else though.
This abomination is an adapter from a 6525 (no spare 6523's) but the mode did not default correctly, so that would have meant kernal changes.
The link you posted was to the project started by MCes, who I tagged above.
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Posted By
SukkoPera
on 2024-02-08
11:57:01
| Re: Weird Floppy 1551 Problem
Sorry, maybe I posted too much stuff and got confusing.
First of all, I would have expected the 6525 to be 100% compatible with the 6523 unless "advanced mode" is enabled explicitly. You probably know about this famous article. Someone even built a homemade paddle with the '25, see this.
Second: yes, I know MCes had started a project to come up with a replacement, and that's what he presents in the F64 thread I linked. But if you read the whole thread, you'll see it inspired some German guys who came up with a full paddle remake, a 6523T replacement in a FPGA and an alternative paddle that replaces that with ordinary 6522 VIAs.
Third: I also posted a GitHub link for an FPGA-based 6523 replacement. If an alternative PCB is made with the 6523T pinout, I bet it will work.
Fourtch: The 6523 is a simple enough chip to be a good candidate for a first attempt at Verilog, mumble mumble... 
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Posted By
Xerox
on 2024-02-10
05:30:44
| Re: Weird Floppy 1551 Problem
Wow, couple of options but actually no "low hanging fruit" 
The green wire definitely goes to D5 and that's the problematic bit that hangs.
Since everything else seems to be working my hope was that there's an easier solution to it.
I don't have the capabilities to create an FPGA based replacement.
For the time being I will have to live with the SD2IEC, but it's not the real thing, you know ...
All my floppy disks are gone for good anyway, which is a shame! Assembler projects and code of 4-5 years lost ...
Luckily you guys found my stuff somewhere and put it online - Thanks for that 
Whenever someone has a brilliant idea, what I could do to easily fix this issue, let me know.
Has someone ever tried the "famous article" that @SukkoPera was mentioning?
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Posted By
SukkoPera
on 2024-02-16
10:07:50
| Re: Weird Floppy 1551 Problem
Looks like the pic posted by @crock above is exactly an implementation of that article.
Anyway I have checked the drive schematics and you should make sure that there is continuity between the two sides of pin 8 of the cable connecting the paddle to the drive.
The D5 signal inside the drive is produced by U3, which is a 6523 (non-pin-reduced version of the chip inside the paddle), so that might have failed, too. You should also check that RP1 inside the drive is still 2.2k. If you have a scope, you should check whether the signal is produced correctly by the drive and then failing in the paddle, or if the signal is already bad at the drive. You can also probably do it with a multimeter if you have a good one.
I can make the shorter PCB for trying that FPGA replacement, but it would be up to you to then order it, get the FPGA, solder and program it.
UPDATE 16/2:
I have been looking at Commodore's original schematics for the 1551 and I have noticed that U3 is indicated as a 6523A, but in actual drives I've always seen 6525's. This definitely hints at the latter being 100% compatible with the former.
Since the 6523T is just a 6523(A) with less pins, it should be replaceable by a 6525(A) just as well.
This is also proved by this video that just popped up, where someone designs a new paddle around a 6525A. I haven't found the project being released anywhere though.
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