HowTo: Adjust analogue part of FDC 279x in a 1050 disk drive

[HiassofT]

I went through my 1050s and checked the write compensation settings (via TP11) on almost all of them.

 

2 of them looked untouched: they had the shield in place and all pots, even the RPM adjust, had their seal intact.

 

The first one measured 251 ns immediately after powerup, 263 ns after 5 min, 265 ns after 10 min and 266.5 ns after 20 min

 

To be sure I checked it with my DS1052E in addition to my main scope, a MSO2072A. Both scopes had warmed up for more than an hour and I performed self-cal before doing the measurement.

 

 

The second one measured 241 ns (cold), 250.5 ns (5 min), 252 ns (10 min) and 254.5 ns (20 min)

 

 

I also found my first 1050 that I bought new back in the 1980ies. I installed a 1050 Turbo in it but otherwise didn't touch the FDC / analog part.

 

This one measured 254ns (cold), 260.5 ns (13 min), 264 ns (31 min), 265 ns (53 min).

 

I also checked 2 of my 1050ies which I modded with a Mega Speedy. In these FDC pin 31 is routed through the CPLD, for simplicity I just checked the CPLD output which runs into TP11 (except for a steeper edges and a minimal phase delay the signal should be idendical).

 

The one with my Mega Speedy prototype measured 243 ns (cold), 252 ns (12 min), 254 ns (26 min), 254 ns (40 min).

 

The one with the final version of the Mega Speedy measured 235 ns (cold) and 240 ns (about 10-15 minutes).

 

I also found a 1050 with a Happy installed that was way off. WPC was at about 440ns and RPW at about 1.5µS - not sure how well this one would have worked without adjusting

 

All of the measurements showed a spot on 125kHz clock. Except for my 1050 with the Turbo that I bought original I acquired all my 1050ies second hand from various places. So even if two of them looked untouched (and I remember several others looking untouched before I installed upgrades in them) I can't be 100% sure that the FDC was still the one that was installed during factory calibration.

 

It would be great if someone else could take measurements as well, my samples don't seem to match Jürgen's - here it's more like 250ns on average and variations between about 240 and 260ns

 

Edit: of course these are all ~35 year old drives, so they can have drifted away from their factory settings, no doubt about that.

 

so long,

 

Hias

Edited September 15, 2018 by HiassofT

[_The Doctor__]

all of the one I have ever seen are between 230.3 and 240.x depending on ice cold or 5 or so min later... who knows maybe they will reach 250 in a heated up drive...

[+tf_hh]

Very interesting these different results

 

But, overall I can´t see any problem even if you use 230 nS or 250 nS. I setup two fine working drives using my instructions in the first post, one with 230 nS setting, the other with 250 nS. Both drives are running for more than 30 minutes before. Both drives are stock drives, good adjusted RPM speed and the same firmware ("L").

 

I take 5 different disks, format them using single density and medium density, write data (all sectors full) and put these disks to the other drive, read them out. If all is fine, I try to write to this disk without formatting it. Works fine. Read back the whole disk in the 1st drive. Works fine. This test I repeat with both drives for all 5 disks.

 

Last test: I put two Minispeedy 1050 into the drives and repeat the test with double density. Also no problem at all - in both directions.

 

When I have had drives for repair with problems using medium density or double density AND something of the adjustments were wrong, then the differences were much higher than discussed here. For example, with one WD2793 I measure below 180 nS and this setting prevents the drive from successful formatting and writing above track 25 approx. Also if people totally screw up all pots, sometimes the drive can´t ready ANY other disk than their own formatted one. And so on.

 

So after all, if somebody has problems with a 1050 drive, it´s a good thing to check the settings. What you use at the end - 230 or 250 nS - may be something like a personal flavour

 

[HiassofT]

Room temperature / temperature drift could play a role. Room temperature was about 25°C here yesterday.

 

 

When I checked the 2 untouched drives I had them completely disassembled, drive mechanics sitting on the table. So the top of the PCB wasn't covered by anything and air could freely vent.

 

On the other drives I just removed the top cover, moved the mechanics a little bit away so I could attach the scope probe and plug in the jumper. During the test the mechanics was sitting above the PCB, so it probably heated up more.

 

so long,

 

Hias

[_The Doctor__]

hmmm, maybe good to note which mech is in use and stepper etc an rom configuration...

[+tf_hh]

hmmm, maybe good to note which mech is in use and stepper etc an rom configuration...

 

I have only Tandon drive mechanics in use. But I´m pretty sure, the result is not dependent on the mechanics nor the firmware. You can do adjusting also with 6507 CPU, 6810 RAM, 6532 RIOT and ROM/EPROM removed without issues.

[E474]

There's an article starting on page 40 of "Atari Magazin", March 1987, on programming a Happy that lists a value of 230ms. It's also quite an interesting article. I think I found it on the Atari Mania site, as a PDF.

 

(posted this to another thread, though it might be useful there too).

[ijor]

There's an article starting on page 40 of "Atari Magazin", March 1987, on programming a Happy that lists a value of 230ms. It's also quite an interesting article. I think I found it on the Atari Mania site, as a PDF.

 

Thanks for the interesting article. I don't see the 230ms value in the article (it's really on page 50, right?). But it may be buried somewhere on the listing and it is difficult to follow for those of us that don't read german.

 

Anyway, if it is 230 milliseconds indeed, and not nanoseconds, then it is something completely different and might be related to the timing of a full disk revolution that it is close to that value, or to some timeout value. Either way it bears no relation whatsoever with the FDC precompensation adjustment.

 

Edit: typo on the timing unit

Edited September 19, 2018 by ijor

[+tf_hh]

Thanks for the interesting article. I don't see the 230ms value in the article (it's really on page 50, right?). But it may be buried somewhere on the listing and it is difficult to follow for those of us that don't read german.

 

I read the article (and the part 1 in the previous Atari Magazin), but there´s no part talking about precompensation. Only the rotation speed of 208 ms (milli-seconds) is named, as you already mentioned.

[E474]

Yes, sorry, was skimming the article. Actually, thanks for the tip on the previous article, just getting on a 2 hour flight!

Edited September 19, 2018 by E474

[pawelkrak]

Hello  im just looking for solution for my CA2001. I just mounted TOMS TURBO and added extra parts to my CA2001 board ( was WD1772). How enable test mode and rest setups are same like 1050?

[xrbrevin]

On 11/20/2022 at 2:29 PM, pawelkrak said:

Hello  im just looking for solution for my CA2001. I just mounted TOMS TURBO and added extra parts to my CA2001 board ( was WD1772). How enable test mode and rest setups are same like 1050?

if its anything like the IndusGT and LDW drives, look for a 5-pin header accessible from the side of the casing. you have to GND the TEST pin to enable calibration mode. the 3x other pins are the signals for your 'scope - 2x for variable resistors, 1x for variable capacitor

[pawelkrak]

On 11/21/2022 at 5:30 PM, xrbrevin said:

if its anything like the IndusGT and LDW drives, look for a 5-pin header accessible from the side of the casing. you have to GND the TEST pin to enable calibration mode. the 3x other pins are the signals for your 'scope - 2x for variable resistors, 1x for variable capacitor

Thanks for answer. You mean 5-pin header (P6): from left close variable resistor is:   H|   R2-.25|   G|  R1-.5|    C1-.4|  .... and should conect H+G ? the rest are for probe?

Edited November 24, 2022 by pawelkrak

[xrbrevin]

10 hours ago, pawelkrak said:

should conect H+G ? the rest are for probe?

hi,

youve found the right pin header. as for which pin is which, see the attached schematics.

 

'H' connects to FDC pin22 - 'TEST' so connect the GND pin here to put the FDC chip into test mode.

 

comparing the diagrams, it looks the same as the LDW drive:

pin 2 (WPW) adjusts via VR2
pin 4 (RPW) adjusts via VR1
pin 5 (VCO) adjusts via VC1

but i'd advise you test your circuit to make sure as i dont have a CA2001 - i have the LDW which is mostly similar and the IndusGT from which they were cloned.

 

 

 

 

 

ca2001circuit.zip

Edited November 24, 2022 by xrbrevin
boot error

[pawelkrak]

10 hours ago, xrbrevin said:

hi,

youve found the right pin header. as for which pin is which, see the attached schematics.

 

'H' connects to FDC pin22 - 'TEST' so connect the GND pin here to put the FDC chip into test mode.

 

comparing the diagrams, it looks the same as the LDW drive:

pin 2 (WPW) adjusts via VR2
pin 4 (RPW) adjusts via VR1
pin 5 (VCO) adjusts via VC1

but i'd advise you test your circuit to make sure as i dont have a CA2001 - i have the LDW which is mostly similar and the IndusGT from which they were cloned.

 

 

 

 

 

ca2001circuit.zip 127.51 kB · 1 download

ThankYOu. Osciloskop working pin WPW,RPW - VCO reporting noises and not working  

[xrbrevin]

3 hours ago, pawelkrak said:

VCO reporting noises and not working  

take multimeter readings of the variable components and/or mark them before you move them so you can always return them to their original positions

do you get any variation on the 'scope readings when you adjust the components?

i only have a handheld oscilloscope and i dont think it operates at the ranges required.

 

the target readings are as follows:

VR2 - 230 nanoseconds (nS)
VR1 - 1.0 microseconds (uS)
VC1 - 125khz / 4.0 microseconds (uS)

 

as far as i know, they are duration readings i.e. the length of the square wave, not the height