1050 with odd problems refuses to read or write DD disks

[trekkie22]

I try to repair a 1050 I just bought. It looked first like a simple issue - from the text of the offer I assumed the drive had a problem with the drive speed. And after it arrived, that was exactly the problem for single density. I adjusted the drive speed and repaired a few broken solder joints and single density worked like a charm with the unmodified drive. I could read, write and format single density and the disks were interchangeable with my other drives without problems. 

 

I then bought a Mini Speedy and installed it - and here the trouble began. Single density still works without problems. But no double density at all. The drive refuses to read, write or format DD disks. It is not the Speedy, tested that with another drive and there it works without problems.

 

I started adjusting the analogue part of the drive as described in tf_hhs post here in the forums. There's a weird thing with the measurements - Other than in the post I have no 125 kHz on Pin 16 of the FDC or on TP10. But the other two signals I can measure just fine and they both have perfect 125 kHz frequency and I adjusted them to a length of 1µs respective 230ns (both were a bit off). But I have this issue with the measurement on Pin 16 on all the drives I have (three in total, including the patient). Speed is bang on 288 +/-0,3 RPM measured with the Speedy System Disk. I measured the RPM with two different original game disks, to be sure that the measurement is as correct as possible.

 

Any ideas what could be wrong with this drive that only breaks DD? I'm a bit lost here as single density works fine and double density is a real big mess. I have done all the basic things - the drive is cleaned and lubricated and I also tried a mechanism of one of the working drives with no difference.

[+Nezgar]

Just to confirm it's MFM in general.... does "enhanced" aka "dual" density also not work? How about without the Mini-Speedy back in stock configuration?

 

Stock 1050 is capable of 2 modes: Single & Enhanced/Dual Density.

Speedy 1050 is capable of 3 modes: Single, Enhanced/Dual, and true double density.

 

It sounds like lack of signal on TP10 might be a factor. Can you try swapping a WDC controller chip from another drive? And test this WDC controller in another 1050? This will normally require re-calibrating as you have done already, or ensuring the original chips end up back with their original drives, but should be "close enough" for a quick test to see if you get any DD (and ED?) capability.

 

Lastly, which WDC controller part number do you have? 2793 or 2797? The Mini-Speedy may not be compatible with 2797.

[+tf_hh]

9 hours ago, trekkie22 said:

But I have this issue with the measurement on Pin 16 on all the drives I have (three in total, including the patient). Speed is bang on 288 +/-0,3 RPM measured with the Speedy System Disk. I measured the RPM with two different original game disks, to be sure that the measurement is as correct as possible.

 

Just to be sure, the following order must be used:

 

1. Power-On the 1050 without mechanics attached (for easier access). Also remove the Speedy or similar

2. While powered on, set a jumper between TP8 and TP9

3. Check pin 16

 

If the jumper was placed before power is switched on, the FDC doesn´t enter the test mode correct.

 

9 hours ago, trekkie22 said:

Any ideas what could be wrong with this drive that only breaks DD? I'm a bit lost here as single density works fine and double density is a real big mess. I have done all the basic things - the drive is cleaned and lubricated and I also tried a mechanism of one of the working drives with no difference.

 

Check pin 37 of FDC and pin 13 of the RIOT (6532) about continuity, these both pins are directly connected. Test (in standard usage mode, with standard ROM or with Speedy) the pin 37 of the FDC. Start DOS, give a single-density format command. Pin 37 of the FDC must be high. If a medium/enhanced density or double density (only with Speedy) format is sent, the pin 37 must be go to low. If not and continuity to 6532 is given, replace RIOT, then FDC itself.

 

[+tf_hh]

3 hours ago, Nezgar said:

Lastly, which WDC controller part number do you have? 2793 or 2797? The Mini-Speedy may not be compatible with 2797.

 

All Speedy versions work fine with the 2797, no issues known.

 

[trekkie22]

44 minutes ago, tf_hh said:

If the jumper was placed before power is switched on, the FDC doesn´t enter the test mode correct.

 

That was the exact issue. I read the datasheet this morning and I found the note: "NOTE: To maintain internal VCO operation, ensure that TEST# = 1 whenever a master reset pulse is applied.". I tried again with that information and the signal is there. I was switching around the drives for comparison without removing the jumpers. It's always the small things that let's you pull out your hair...

 

Thanks for the further help, I'll test the connection between RIOT and FDC.

[trekkie22]

11 hours ago, tf_hh said:

Check pin 37 of FDC and pin 13 of the RIOT (6532) about continuity, these both pins are directly connected. Test (in standard usage mode, with standard ROM or with Speedy) the pin 37 of the FDC. Start DOS, give a single-density format command. Pin 37 of the FDC must be high. If a medium/enhanced density or double density (only with Speedy) format is sent, the pin 37 must be go to low. If not and continuity to 6532 is given, replace RIOT, then FDC itself.

Fixed it! I forgot one of the basics with old electronics. I measured the connection and it was broken. Just needed to reseat the FDC and now the drive works  Thanks a lot!