PHP 1250 NOT READING OR WRITING

LouisB · May 2, 2022

23 minutes ago, Ksarul said:

Note, the error would be 61 if the Write Protect sensor isn't working. Your problem is probably with the ability of the head to write (or in this case, lack of that ability).

On PC drives in place of TI drives, the answer is: it depends. HD drives (1.2M) do not work with the TI, but DD (360K) drives work fine. Stay away from 3.5 inch drives for now (they can be used, but there are a lot of quirks to be aware of when doing so). The combinations drives (a 5.25 and a 3.5 in the same housing with a single half-height faceplate) almost never work with a TI and should be avoided.

Thanks for that, I tested formatting a write-protected disk and received the correct Disk Error 44 in Disk Manager (same as I/O Error 61 in basic)

I just found the schematics for this drive here (MPI Model 51) so I'm going to dig into that.

p.s. I was fibbing a bit when I said I didn't have another drive, I have an identical PHP-1250 but I wasn't counting it because the head moves, but drive motor doesn't spin the floppy. Now that I have these things apart I noticed that when swapping the boards between drives the mechanisms have the same behavior depending on the board (both mechanisms seem fine I mean, PCB's are the issue) Point being I'm going to first take a look at the motor circuit and see why the one PCB doesn't spin the floppy, seems like a simpler thing to track down?

Edited May 2, 2022 by LouisB

LouisB · May 5, 2022

While I'm waiting for some parts to arrive I hooked up an older 360K PC drive to image some disks using Nouspikel's software and connection cable I made up using his instructions. DSK-PC/O sure gives this old PEB a workout!

Edited May 5, 2022 by LouisB

LouisB · May 21, 2022

I did manage to fix my drive with this issue. Fortunately the Product Manual is very well written, spelling everything out and even including schematics, timing diagrams, troubleshooting steps etc. so working on these is quite enjoyable. I’ll also include an additional scan of the manual I found online which is better (and worse) in some places compared to the one I found on the forum, as the scans get blurry in certain places.

The fix for this one was to replace chip 1A / RCA CA3054 Differential Amplifier (circled in the picture below.)

I found this chip was bad by simulating write data using an Arduino putting out a 2µs pulse. The Signals to the R/W heads were totally flat. Luckily I had a working drive handy to compare signals, otherwise I don’t think I would have been so sure about the problem!

Here’s what the signal should look like on the heads when feeding in a simulated write pulse, and can also be checked on pins 1 & 14 of the CA3054 :