tep392

This post is a bit old, but I wanted to let you know what I found about the Tandon fast seek steppers. I have two Tandon TM50-2FS PC drives. They both are the Fast Seek version and I just installed them in a Percom drive. I also moded the Percom ROM parameter that reduced the seek delay. I've had no problems with it it so far. One drive has a 211005 stepper and the other is a 210323 like your 1050's. So your 1050's might be capable of fast seek. An important detail is the tuning of the one shot's used in the stepper control. The TM50 service manual is available online and the schematic has details of the differences between the fast seek and standard versions. It's basically just two caps and a resistor. I haven't looked at the 1050 schematic, but if it uses a similar driver configuration, then you might be able to identify the equivalent components that would need to be updated.

I noticed it pop up on one of my saved searches the other day. Nice work!

I now have 720K of storage in my Percom! I noticed that the new 5V/12V regulators I installed for the second drive run quite a bit cooler than the original regulators. I had assumed the heat load would just be a function of the voltage dropped and current draw, but it seems the new parts are more efficient as well, so I might go ahead and replace the originals to reduce temps. I could also spend a bit more and change to switching regulators. I did that on my 1050 drives and they run cool now. No more warm floppy disks.

That is strange. The schematic also shows both ports are the same.

I've checked that both SIO ports work identically.

I have a question for the kryoflux experts here. I have an old Monroe OC-8820 business computer that uses a proprietary form of the CPM operating system. I don't have any bootable disks but there are disk images online in TD0 format. The machine uses Micropolis 5.25" drives that have the standard 34pin edge connector used on old PC drives. I was actually able to connect the drive to my Atari using my Percom drive as the interface. Would I be able to use a Kryoflux to write a disk image to the drive? Does the Kryoflux software work with TD0 images or would I need to convert it to something else? Thanks!

The seller myatari on Ebay is Bruce from B&C Computer Visions. He has tons of NOS Atari stuff that he bought from Atari years ago. He has Dos 2.5 on SD disks that will work with your 810 drive. The DOS 2.5 disks that were packaged with the 1050 drives were ED formatted and only boot on the 1050 drives, so be careful what you buy. Avoid Dos 3.0, which doesn't support SD. Atari DX5075 DOS 2.5 SINGLE DENSITY SD Master 5 1/4 disks 2 each for 800,XL, XE | eBay

I was able to put my Percom drive to good use tonight. I have an old Monroe OC-8820 business computer. It uses a proprietary CPM based OS and has two Micropolis 96tpi SSDD 5.25 drives. I don't have any software for it and the video isn't working at the moment. I haven't tested the drives either, so I decided to try connecting them to my Percom controller. In SDX I used the setting for SSDD 80 track, which at 18 sectors/track is 360K, and was able to format a working disk. It was cool to use my Atari to test the CPM machine's floppy drives.

Feedback belongs in the comment section. I have edited the title.

I decided to pick up an inexpensive logic analyzer this week. The Kingst LA2016. It's actually pretty impressive considering the price. My first test of it was to analyze the bitstream and sector layout of my Percom drive. Based on my measurements, it looks like the Percom uses the same bitrate and sector spacing as an Atari drive, so it should be appropriate to run the Percom at 288 rpm. If Percom intended the drive to run at a faster speed, then they should have increased the bitrate to allow the same number of bits per track as an Atari drive. I adjusted my Percom down to 288 rpm and it's running quite well.

I believe the various drives have different ROM's. Phaeron posted a summary of the revisions HERE. If your AT88 has the hardware for the side select signal, then it may also have the same ROM parameters that allow the default number of sides to be set. We should be able to confirm if a disassembly was done for the ROM.

The ROM is for the S1PD and SPD models. Which AT88 do you have?

I'm able to write to both sides of the disk, but there is a quirk. This was all done with SpartaDOS X 4.49. I started out by formatting a disk for DSSD. I wrote files to it until it had about 150k of data. Then I formatted a disk for DSDD and wrote about 290k to it. I shut down the drive and computer for a bit. When I went back to use those disks, I could no longer read or write side two of the disks. CHKDSK would properly identify the disks as double sided. I decided to format a third disk as DSDD. After doing that, I could again access side two of the disks. Very odd. I'm wondering if one of the later ROM revisions fixes this. Mine has V1.11. I've seen that there is a V1.21 and some later version that Jeffrey Worley has. Maybe I should give those a try. Edit: I've decided what I am going to try. I'm going to burn a ROM with "Percom AT88SPD 575C9833.BIN", which I think the the latest known revision and I will modify the default step rate to 00 and the default sides to 01 (sides-1). My Tandon TM50-2FS has the fast seek option with 6ms seek time, so defaulting to to 0 step rate should be ok. Edit 2: I burnt the "Percom AT88SPD 575C9833.BIN" ROM with the changes to default step rate and double sided. It seems to have resolved the issue of being able to read/write the 2nd side. The SDX Format command also defaults to double sided now. Next step is to add the voltage regulators and second power cable so I can put a second 360k drive in it.

I checked the drive that came with the unit and it's running at 296 RPM. I don't know if this is the original Percom setting or not. The drive mech had a single terminating resistor inserted in it, which looked like a bodge to me, so the drive might have been messed with at some point.

The AT88-S1PD is working! I replaced the buffer chips and it started communicating with the 800XL again. The original 180K drive is still not working so I put in a Tandon 360K drive. I'm able to format in SD or DD and single or double sided. I've tried booting single and double density disks without problem. It is a bit flaky though. Every once in a while I get a 139 NAK error. When I have some time I'm going to check all the adjustments. The RPM on the Tandon unit I installed is the standard 300 used for PC drives. Does anyone know what speed Percom adjusted their drives too?

I found the bad chips! There are three 7406 Inverter Buffer IC's that are bad. They are used primarily for the printer port, but there are a few gates used for some of the drive control signals and the TxD signal from the 6850 to the SIO port. I'm guessing that something was attached to the printer port at some point that fried those three chips. I won't have replacement parts until next week, but hopefully that is all it takes to resurrect this drive.

This is the ROM from my drive. AT88S1PD_V1.11.BIN

I've wanted one for a while now. I think I can get a cheap USB unit for under $200 that will do the job.

A logic probe can only tell me if there is activity in a signal, but I'm pretty sure the CPU is reading data from the 6850. I can't tell with the probe if the CPU is trying to send data back to the computer. Maybe it's time I invest in a logic analyzer.

I tried both ports and get no response from either.

Here's an update. I fixed the index sensor on the drive and confirmed it is working when connected to a PC. I put it back in the Percom and I still get no response from the drive when I try to access it using SDX on my 800XL. Error code 138. The drive doesn't spin up when receiving a command and appears dead so there is a problem with the Percom controller. I started probing around with my logic probe and scope next. The power supply voltages are still good and there is a clean clock signal. The next thing I checked was communication over the SIO to the 6850 ACIA. The 6850 is receiving a serial transmission from the Atari, so the logic chips in the data path seem to be working. I can also see the data bus lines start toggling in response to SIO commands, which should mean the CPU is polling the 6850 and reading data from it. I don't see any activity on the 6850 transmit pin back to the Atari. That's all I've checked so far. I'm not very familiar with SIO commands, but maybe there are commands other than format/read/write that would expect a response from the drive. Something that I could use to check for a response from the CPU. The FD1795 is socketed, so I would just try replacing it, but sadly I don't have any replacements. edit: I forgot I have an 810 diagnostic cart. I tried the "drive select test", which just checks the drive switch settings, and it gives an error message that the drive is offline.

I'm keeping my fingers crossed that it works when I get it back together. If not, I'm confident I can troubleshoot it and locate the faulty part(s). I'm an electrical engineer and I won't allow the electronics to beat me.

I've tried testing the drives on an old PC with Dos and Win XP. - Original MPI drive is not moving the r/w head. With power on, the stepper motor can be easily rotated, which would indicate either the motor or the drivers are not functioning. BIOS doesn't have a 180k 5.25" option either, so can't properly test. - Tandon 360K drive. I bought this one to add a second drive to the Percom. It spins when commanded to and the r/w head will seeks properly. I don't have any DOS formatted disks to test, so tried formatting a blank DSDD disk. In DOS it tells me it's checking format, then give a message "not ready". In XP, the drive shows ok when I check it's properties. When I try to format it, the drive starts spinning but a few seconds later I get the message "there is no disk in drive a:. Insert a disk and try again" I've never troubleshot a PC floppy drive before, so need to look for a guide. Maybe there is some software to help me out. I have the field service manual for the drive, so will need to dig through that also. Progress report 1: I downloaded ImageDisk and ran the TESTFDC program. When it tried to format the disk it gives a message "no FDC interrupt". Could this be a DOS configuration issue? My DOS PC skills are weak. Progress report 2: I found the problem with the Tandon DSDD! The index signal wasn't working due to a broken lead on the LED of the sensor. I fixed it and was able to format, write and read a 360k disk (installed in a PC)! Then the wire broke again at the base of the LED. I'm going to wait until I can get a replacement LED before I put the Percom back together for testing.

I’m using SDX and checking for a response to every possible drive number. I ordered a PC cable so I can test the drive on my pc. If it works then I will know the problem is in the Percom control board.

Yes. It spins the disk for a little bit when I close the lever. I'm thinking I might test the drive on my old PC. It's a 90's era machine with a 3.5" floppy drive. Maybe I can use it if I get the correct cable. EDIT: