Building a Commodore 64GS
12 November 2022
Adapters 72-60 PINs NES-Famicom
December 23, 2022
I'll take a 1571
After having had a Commodore 1541 for so many years and then the later compact 1541-II version, it's time to try the 1571 stand-alone!. Yes, because I actually have a 1571 but it's inside a Commodore 128D and here you can find the repair article: Repair-C128D
This version is like the 1541, big, heavy, with internal power supply, but the drive has 2 heads to read the disk and this is its great novelty. The 1571 was introduced to accompany the Commodore 128 and offering a new drive that was faster and more capable of reading multiple formats, as well as being able to handle both sides of the disk as one.
This drive in the new 1571 mode (usable natively if connected to the C128) allows you to have a 1328 block disk, without having to turn the side because both sides of the disk are used as well as greater speed. Of course, to make it compatible with the older system used by the C64, it also has the ability to emulate 1541, which it does automatically when connected to this computer.
Well after this introduction on what a 1571 is, let's get to the point.
I look for some offers that are not too expensive and I find one that doesn't work:
Defective, drive always works, floppies not read ⭐⭐⭐⭐⭐ not working, defective, drive always works, floppies not read"
Yes, I want!
I didn't know the flaw, but I knew that the drive was spinning all the time and not reading anything. In these cases it is often a logical and not a physical problem, externally it was in excellent condition, just a little dirty but perfect.
But will I be able to make it work?
Repair
Ora che sappiamo tutta la sua storia e poco ci importa 🙂 andiamo a ripararlo…
PS: did you know that you can see the repair video of this drive?
Go to YouTube and search for Retrofixer, subscribe to the channel and watch all our repairs, tutorials and other videos!
The first thing we see once the drive is opened is its power supply with the disk drive in front of it, we remove all the screws in order to then disconnect the power supply and remove the card that is underneath everything.
The first thing I do is test the drive to physically see what happens, if the LEDs stay on, if it resets when connected to a computer, if it responds to commands.. already! the failures can be similar but have different behaviors and to begin to understand what to look for it is necessary to analyze the symptoms.
The drive turns on, the motor turns, the activity led turns on..
after a few seconds the activity LED goes off (correct)
the engine continues to run (mistake)
Up to here we already knew it, but the activity LED behaves normally, while usually it either stays on or should stay off.
Second test, I connect a C64 to the drive and try to turn it on when the drive is already running, normally the drive should reset itself, if it doesn't I could hypothesize a problem with the circuit that controls the communication..
Ok, the drive resets correctly if I turn on the 64, but it still spins.. well, I can bypass the communication logic and continue with the tests. I run the command to read the directory (load”$”,8 since the drive is set as unit 8) and the drive responds to the command, moves the head and then immediately gives an error by flashing the leds.
From this simple test I can understand several things, the drive communicates in some way but it doesn't have control of the motor, I feel like excluding the CPU, the ROM, the RAM and the part of the logic that communicates with the computer.
Now there are still several things left to see such as the VIAs, disk controller and other drive related logic.
With the help of another drive I can test the one socketed chip without problems and in zero time, but this one is good.
As per the manual, however, I check the power supplies, the clock and the reset signal, just to be sure of being able to exclude a part of the logic, but if the drive communicates, the CPU works and the clock must be there!
Another thing I can do without using another drive is to swap the VIAs, they are the same and so if the fault changes we immediately have a clue. If they were both broken this method would not help us and we will be forced to test these chips in another way!.
The VIAs of this drive can be found on another 1571, even inside a 128D, in its drive, or on an Amiga 500.
Well, I exchange this two chips and .. TADAAA!
The defect has changed, now the drive initializes and the disk stops, but now if I try to run a command to read the directory, the computer crashes.
The defect is on one of these VIA! with the help of an Amiga500 I replace the broken chip and the drive works perfectly.
Now all that remains is to try it in 1571 mode to see if the second head works too, but I'm testing it with a C64! how can I do? Easy, there is a command to be able to send it to 1571 mode:
OPEN 15,8,15,"U0>M1":CLOSE 15
Now that I'm in 1571 mode, however, I don't have any disks formatted this way to verify it!
Well let's take an empty disk and format it in this way so instead of having a side of 664 blocks, we should have a whole disk of 1328 blocks, but always limited to 144 files.
OPEN 15,8,15,"N0:TEST1571,F1":CLOSE 15
Once formatting is complete, we load the directory and see how much free space we have on the disk.
Formatting gave no errors and the directory shows us a disk with 1328 free blocks … Yuppie!!!
Perfect, repaired drive and at a low cost since this spare part is fortunately still available and they are also making it from new, the W65C22N6TPG-14 which you can purchase from Mouser. Obviously I got one because I want to see if it actually works, as soon as I text it I'll update the article… stay tuned!
I didn't have this chip and I got it on Aliexpress because in Italy I found it at a bit too high prices, I didn't want to remove it from the 1571 of my 128D so I thought that while waiting for it to arrive I could check if its predecessor worked.
I'm talking about the 6522, the famous VIA that can also be found on a 1541 first and second version, but there is a problem, this chip on the 1541 works at 1MHZ, will it work on the 1571 which works at 2MHZ?
Tested and working! at least with 1541 mode, but I think there is no difference since the clock does not vary with 1541/1571 mode.
To help you with the repair, I leave you the 1571 manual and the guide written by Ray Carlsen, you will find information on the 1571 but not only: https://portcommodore.com/rcarlsen/cbm/1571/
