Very Strange C= 1571 Drive issues...

Nathanieltolbert

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Hello everyone. I had a local commodore 8 bit user give me a bit of hardware last week and I have been battling with a strange issue I have. Let me give you some details. As I stated earlier I went up about two weeks ago to Raymond Computers in Minnesota, the gentleman with all of the Commodore hardware and software. I bought a C128 set up while I was there. I didn't think my wife would let me get away with a 1571 drive as all he had were boxed, unopened drives, and so they were going for a fair bit. So the Tuesday after I got back while recovering from a cold I was talking with a friend of mine and he said there was a commodore user group member that was wanting to get hardware to people who were willing to use it. So we called him up and he gave me another 1541, a 1571, a C64 old style, and 2 (defective) C64c models. After some work I identified what was wrong on one of the C64c models and had it up and running nicely. Sadly the other one won't even turn on at all. Black screen. Anyway back to the 1571. Here's the strange thing. I plug it into my C128, and it says Device not present in both 64 and 128 mode. I plug the same drive into my c64 either the old style or the c style and it works perfectly fine, like a 1541 drive. So I'm scratching my head as I would assume since so much of the logic and controls are covered by the same chips inside the 1571, that the drive should work in both 1571 and 1541 mode. Has anyone heard anything like this before? If so, is there a fix for it? Thanks for any info you guys can provide!
 
Does the C128 works with any other drive with no problems?
 
Yes, I have two 1541 drives on it. The only software I seem to have issues with is mindscape software that uses the V-Max software acceleration. Everything else works. And the interesting thing is that the V-Max works in one drive but not the other. And both 1541 drives I have work perfectly fine on both C64 systems I have. It's very strange..
 
@Nathan

Does the 1571 have it's original firmware ROM or has a 3rd party "JiffyDOS" been fitted.
Also ensure the 1571 is set to device '8'

TC :cool:
 
It would help narrow down the problem if you can get another 1571 or C128.
The serial HW in the C128/1571 is different than C64/1541 & it looks like your C128 & 1571 are not able to communicate.

Please try the following:

- Power down both C128 & 1571.
- Turn on your C128, in C64 mode (hold C= key during power-up)
- Power on the 1571
- Try reading a C64 disk (single side)

Another thing to check:

Make sure your C128<->1571 serial cable has pin-1 connected!
This pin is not used in C64/1541 but is required for 1571 (its a fast serial clock for Burst-Mode).
 
@The Corfiot - I don't know if it has a jiffyDOS chip installed, as I haven't a clue where to look for that.

@Uber-Freak - The cable I have has all 5 pins on both sides. I tried the whole booting into c64 mode then turning on the drive, and it doesn't work says device not present error. I know 1571 drives work on this 128 because we used a 1571 drive during the first part of testing at Raymond's up in Minnesota before going over to the 1541 to calibrate and confirm working status. So I know it can work with a 1571, just not this one.
 
@The Corfiot - I opened the drive and carefully unscrewed the power supply. In the U2 Socket is a different looking chip. Looks like an EEPROM. Has a label with the following numbers on a sticker over the middle of it. 310654-03. The actual chip says the following:

Japan 8520
00009ss0
PGM 12.5V
HN27256G-25

The only reason I ask about this is because it looks completely different from every other chip in the drive. Is this a modded chip?
 
I researched carefully the issue I am having and have found a website that identifies what might be causing the problem.

U19 logic 74LS241 Normal startup but 1541 mode only (read, write, format OK), no 1571 mode.
U20 CIA 6526A or 8521 No 1571 mode but normal startup, read, format and write in 1541 mode only.


This sounds exactly like what I'm encountering. Works perfectly fine when used on a C64 because it runs in 1541 mode, but no 1571 mode whatsoever on the 128. I have identified both chips on the board and the 6526A is socketed but the 74LS241 is not. Is it even possible to source replacement chips for these? I think it would be an interesting project for me to try.
 
Last edited:
Check the cable prior to blame anything: even if the connectors have the pins, the pin #1 may be not wired or maybe even have a cold joint/broken connection.

The JiffyDOS EPROM chip ( a ceramic chip with a label over) is easy to spot, as it replaces the original ROM (no transparent circle window, full-plastic black chip) inside the drive.

Pretty much the same as an original Amiga kickstart chip compared to an EPROM burned replacement.

[EDIT]
The 74LS241 is an ordinary TTL chip, available pretty much everywhere. In the event you can't locate an LS part, search for 54LS241 (military spec TTL equivalent: no mil spec jokes, please) or the 74HCT241 (CMOS remade of the same chip).
 
This serial cable I am using is the same one we tested the 1571 on up in Minnesota, is it possible that bringing back from there caused it to be come damaged? Do I just use the multimeter and check to see if a current goes down each pin to test for breaks? What settings should I use?

-edit any ideas on where I could source the 6526A chip? In case the cable isn't bad?
 
If the CIAs are the same ones as the 1541, try asking TheCorfiot if he still has the ones on an old 1541 board I sent him, when he was repairing his drive. I don't know if the CIAs were working at all though.
 
This serial cable I am using is the same one we tested the 1571 on up in Minnesota, is it possible that bringing back from there caused it to be come damaged? Do I just use the multimeter and check to see if a current goes down each pin to test for breaks? What settings should I use?

Put the tester as continuity (the place where is a diode icon) and put the probes at each pin #1. You'll hear a buzz if your tester have one, but the LCD tester panel will show 0000 (or near it) if all is OK.

Also remember to test the pin #1 against the shield (outer connector metal)! A short to ground will kill outputting devices (like the maybe problematic TTL chip).

One probe on pin #1, the other on the metal connector.

-edit any ideas on where I could source the 6526A chip? In case the cable isn't bad?
6526A? Is the solution not related to replacing the TTL 74LS241 chip?
 
Hrmm... From the schematics that I can look at (low res, low quality hard to read) it doesn't appear that the 6526A chip is used in the 1541 drives at all... I could definitely be wrong on this as the schematics weren't the best, but I didn't see it. Now the 74LS241 is used, but that I can get than new for pennies and buy several spares for possible future failure.

I did find a place to source replacement 6526A chips, but man alive are they expensive. I won't say how much but let's just say it's more than I got my Whole C=128 setup with monitor and drive for!!:eek::wooha:

There's got to be more places where I can source one of those chips that doesn't cost so much.

-edit- @RKauer - it could be either or both of the 74LS241 or the 6526A chip as they both show the same symptoms. Better to have both and be prepared than to find out I got the wrong one. I can see how you missed that I had both listed. The formatting went wonky after I posted. I fixed it now for easier reading. Yeah, it could be either chip, or both, and I cannot truly tell. So to test the pins, use my multimeter?
 
@Nathanieltolbert:

6526A is the 2Mhz version of the 6526, you can find it in C128 and possibly even in newer C64 units (C64C)
Dont put a 6526 instead of 6526A, it will fail or die.

@rkauer:

In the 1571's case its quite normal to find EEPROM chips as the original ROM had bugs in its 1541 emulation mode & sometimes fixed ROM versions were sold by retailers on EEPROM.
For example, in my country all C128 units were sold with EEPROM ROMs because a hebrew charset was added to the ROM (dont know if by the local importer or by C= itself).
 
@Uberfreak - Yes, I had located and identified that the there is a difference in the speed of the 6526 and the 6526A variant and that although if you need to replace the 6526, you can somewhat safely use the 6526A, you cannot do the opposite.

@RKauer - I tried testing the cable and I am apparently testing it wrong as it doesn't get anything on any of the pins. I know the cable works as I am using it right now on the 1541 drives on my 128 right now. I'm confused.
 
1541 Uses 2x 6522A sadly otherwise you would be welcome to some spares I have (for my Acorn BBC's :shhh:)

6526A is essential for the fast serial operation, I would try the logic chip first as it is the cheapest & likely suspect. the 6526A is still used in slow mode but in a different config.

When the C128 / Controller is reset it sends a high speed Byte ( 8 pulses ) via pin 1 of the serial bus (not used in C64) & awaits a response if no response is received then slow mode operation is set.
In a similar fashion if the 1571 does not receive this high speed byte it also reverts to slow mode operation as it assumes it is connected to a C64.

TC :cool:
 
Cool. I'll source the 74LS chip since it's all of 50 cents. Anyone else want some for spares? I'm going to have to order a minimum of 10 from JameCo to do an order.
 
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