Commodore1551 Floppy Repair: I built a whole new interface!

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Thanks to pcbway.com for supplying the pcbs used in this video.
The 1551 was Commodore's attempt at making a parallel disk drive for the TED series computers. Unfortunately it was tied to the TED machines by specific hardware, so it never got wide adoption.
I got this example "untested" (ie broken) in a job lot, and in this video I'm going to try and get it working.
But what do you do when the only dead IC is one that is completely unavailable? Watch to find out...
Commodore History's benchmark video: • Update to my previous ...
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00:00:00 - Introduction
00:01:23 - Teardown
00:04:09 - Fixing the Door Latch
00:08:22 - Inside the Paddle
00:09:47 - Power itUp
00:13:50 - A Test Program Off the Internet
00:19:36 - EEPROM Programming
00:22:20 - Dismantling the Paddle
00:25:45 - EEPROM Adapter
00:32:36 - Testing the EEPROM PLA
00:34:43 - Interlude: Case Repair
00:40:33 - NEW PLA Test
00:41:50 - Let’s Just Try The Drive On Its Own
00:43:11 - Scope Tests
00:46:38 - Enter PCBWay…
00:47:24 - And A 6525 From Poland
00:53:23 - Test with New Cartridge
00:55:35 - A New Test Program
00:59:29 - New Test with Old Paddle
01:01:08 - Transferring the Cable to the New paddle
01:05:57 - Test: Drive + New Paddle
01:09:23 - Retest the Original PLA
01:11:22 - Performance Test and Benchmarks

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Опубликовано:

8 июл 2024

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Комментарии : 49

@PCBWay 4 месяца назад

What a fantastic job you just did!

@CaptainCommodore 4 месяца назад

Great job on this tim glad it worked out in the end

@chainq68k 4 месяца назад

Seems Big Brother Google knows my love for the 264 series (first computers I ever used at age 8), so for once I'm thankful that a new channel was recommended to me, and it was yours with a 1551 video no less. Great work with the drive and the paddle. I have a 1551 in storage that I haven't dared to touch yet, all the knowledge you shared will be a great starting point when I finally dig into it. Thank you!

@dinkc64 4 месяца назад

Great work, buddy! I always wanted to see the workings of a 1551 drive, thank you very much!

@michaelcarey 4 месяца назад

Fantastic work! Recreating old tech shows great dedication. Back in early 2022 I went though the process of reverse-engineering an SX-64 I/O PCB. I was restoring an SX-64 and the I/O board was full of corrosion. Not being able to find a readily available replacement, recreating was the next step. I was lucky that I was able to find a PCB engineer wizard lurking in my amateur radio club :-)

@TimsRetroCorner 4 месяца назад

Modern PCB fabs and tools are so cheap and accessible, I'd never have been able to do that a few years ago!

@JosipRetroBits 4 месяца назад

Wow, this is tremendeus amount of work on this interface, nice job :) Cheers!

@TimsRetroCorner 4 месяца назад

Thanks. I still have to build a case for the new interface (as well as make some tweaks to the pcb)....

@xenoxaos1 4 месяца назад

ABS can be solvent welded back together it can also help messed up threads by mushing it all around. 38:00

@3vi1J 4 месяца назад

Now that's really going the extra mile! Great job!

@GadgetUK164 4 месяца назад

Great job!!! What a mare that was to get working lol

@craftsman123456 4 месяца назад

How cool. Great Job on the pcb. I've always wanted to find a 1551 for my setup

@tommyovesen 4 месяца назад

Wow that was really impressive work Tim. I have a couple of Plus4 and C16's, but I never hade a 1551. Interesting video.

@TimsRetroCorner 4 месяца назад

This is my first 1551, so of course I was determined to get it working!

@TinySmall69 4 месяца назад

Good job, the bad thing about this interface is that it's still bit-banging, and as far as I remember they don't use IRQs for the handshaking, but I'm not sure it's some time that I looked at the code.

@mondo8bit 4 месяца назад

Cool Project and great work! 👍

@DaveCurran 4 месяца назад

Device 8 or 9 is selected on the drive (cut a trace between two pads next to the 6525). This is sent via pin 2 of the drive cable. That is used by the PLA to select FEFx or FECx. With no drive connected, that will float, so may explain some of the problems you were seeing on the paddles with no drives connected. If you pull that low, that might make the test program work (or at least be more consistent if the 6523 was faulty).

@TimsRetroCorner 4 месяца назад

Because it acts as an address input on the PLA, and while it is pulled up, it's pulled up inside the drive. Yes that makes sense.

@TimsRetroCorner 4 месяца назад

I reran the test program with the drive cable disconnected and a pull-up on pin 2, and that gave (mostly) correct results (there were occasional 'Bad / unstable' flags, but they weren't consistent between runs). Thanks @DaveCurran

@fumthings 4 месяца назад

not that i think it matters for the logic test, but the "program from the internet" tests the registers for FECx in every case in the video. i think that program later asks which drive, and then changes the value to FEFx if required. its a bit like that program was written assuming the 1551 drive was going to be an additional drive that was changed to dev 9.

@DaveCurran 4 месяца назад

@@fumthings when the drive is powered down, pin 2 will be low, which indicates drive 9, so it is correct to test FECx until the drive is powered on and pin 2 goes to the correct voltage. (my 1551 passes all the tests on that program)

@fumthings 4 месяца назад

@@DaveCurran ah, thanks, that all makes sense now.

@DaveCurran 4 месяца назад

I see I'm not the only one with a 1551 in bits on my desk this week. Interesting.

@GeorgesChannel 4 месяца назад

Great video Tim! I have a faulty 1551 too. Maybe i can pin the bug down now with what you showed here..

@TrimeshSZ 4 месяца назад

One of the first products I worked on used that PLS100 chip back when it was still a Signetics product - admittedly, we were using it as a state machine and running in on a fast clock, but it quickly got a reputation from the service people as a "replace on sight" part. I've been sort of biased against them ever since.

@TimsRetroCorner 4 месяца назад

same thing now with MOS branded logic.

@TrimeshSZ 4 месяца назад

Yeah, MOS had a lot of problems with passivation, especially early on. For example, the MOS 6550 1024x4 SRAM that was used in the original PET was especially bad.@@TimsRetroCorner

@kaunomedis7926 4 месяца назад

I think, that PLA must fit to a bit more "modern" chip without problem. The only problem, that greedy people hide information :)

@TimsRetroCorner 4 месяца назад

More likely greedy sellers on fleabay gouging the prices of original chips. People that do actual work to produce things are worth paying for their time and effort and skill. And that includes reverse engineering stuff.

@kaunomedis7926 4 месяца назад

@@TimsRetroCorner It is a pitty I don't have 1551. I can do the reverse engineering and do it opensource. :) And I just looked in bay... the only available is 300+ wow!

@wimwiddershins 4 месяца назад

Cart connector continuity was nagging me while watch this until 55:00 Also, check grounding on your soldering station, I have the same model and it came with a loose ground inside. 😬

@Daveyk021 4 месяца назад

Great job! When you designed a new board, why didn't you design it around the 27512 EPROM? That is a lot easier to find and make than getting a PLA chip.

@TimsRetroCorner 4 месяца назад

Because I had the PLA, and I had no proof at the time that the EPROM solution worked.

@Daveyk021 4 месяца назад

@@TimsRetroCorner That PLA can't be that easy to get either or is in short supply. For the C64, two GAL chips are used to replace the PLA (I guess more or less the same as an EPROM, just a cross or table. That might be something to try to breadboard for all 10 of these drives that remain out in the wild - lol.

@TimsRetroCorner 4 месяца назад

@@Daveyk021 Wasn't that hard to find (as a programmed up PLS100), just a bit pricey is all. Once I've checked the EPROM I made works (shouldn't have been so quick to put back the cartridge shield, lol), when I lay out the Mk2 board, I can add an eprom footprint and give people the option of either.

@kaunomedis7926 4 месяца назад

@@TimsRetroCorner "just a bit pricey"... show that equations! Make it opensource and everybody can program any programmable thing to emulate PLA.

@Stoney3K 4 месяца назад

Sounds like maybe you can modify the paddle to have a IEEE-488 port? That would more or less explain why the cable to the drive is in that staggered "D-sub" shape.

@TimsRetroCorner 4 месяца назад

You probably could, but the protocol is not IEEE-488, so you'd also need to rewrite the DOS. At which point it might be simpler to convert a 1541 (there are conversion PCBs & ROMs available for that)

@Stoney3K 4 месяца назад

@@TimsRetroCornerSo in some weird way they made up *another* protocol besides 488 and their own serialized version of 488?

@kenknight5983 4 месяца назад

Do you have a usb 3.5 inch floppy drive? The Pi1541 is supposed to have experimental usb support for thumb drives, but I don't think anyone has experimented with a usb floppy drive

@TimsRetroCorner 4 месяца назад

Funnily, I was just thinking about that in another context. It'd be fun to try...

@kenknight5983 4 месяца назад

@@TimsRetroCorner unlike 5.25 disks, 3.5 inch disks seem to be surviving. Might be an affordable method for those of us who want to use real floppies. Any ideas?

@tommyovesen 4 месяца назад

How much faster is the 1551 compared to the 1541 without fast load?

@tommyovesen 4 месяца назад

Haha, you already answered that in the end of the video! I asked too quickly :)

@TimsRetroCorner 4 месяца назад

lol

@Stoney3K 4 месяца назад

@@TimsRetroCornerHow does it compare to the C128/1571 burst mode transfer?

@Stefan_Payne 4 месяца назад

You really should look for a ZD-915 and invest in it. It would make your life much easier and its not very expensive, over here it was ~100€ shipped.

@TimsRetroCorner 4 месяца назад

I have one (you can see it on my bench at various points in the video), but I rarely use it because it's always clogging up and a right PITA to clean. Maybe a genuine Hakko would work better, but those are expensive!

@Stefan_Payne 4 месяца назад

@@TimsRetroCorner Interesting I didn't have that issue with mine. And I just did a capjob of a Mega Drive one with it... However, I added a bend, holey Metal Plate from my old Xytronics LF8800 to the ZD915. (for the price, its pretty bad due to the weak pump) Maybet hat's why it didn't clog? At least not nearly as much as the Xytronics...