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Corcomp 9900 disk controller problems


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#101 RickyDean OFFLINE  

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Posted Fri Aug 5, 2016 10:57 AM

It's to late for that, though I still have the hardware. Do you think I would get a good reading out of circuit?



#102 justacruzr2 OFFLINE  

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Posted Sat Aug 6, 2016 1:08 PM

It's to late for that, though I still have the hardware. Do you think I would get a good reading out of circuit?

 

I'm assuming that means you already removed it.  No matter...also assuming that it's being supplied with 5 volts when on the board so you still should be able to see what it's allowing to get thru off the board.  The middle pin is the wiper so you want to get a reading between the 2 outer pins.  Because I'm not sure which direction voltage is being supplied to the trim pot (which outer pin...unless the trim pot has a "+" sign over one of the pins) you may have to try both ways.  Try supplying 5V to one side and take a reading on the other side.  If that doesn't work, or you get an odd reading, try reversing the test leads.  Also assuming your tester can supply 5V thru the positive lead.

 



#103 Stuart OFFLINE  

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Posted Sat Aug 6, 2016 1:49 PM

 

That's basically what I did too.  Everything on my board is new except for the PAL's, the crystal, the ribbon cable socket and the 8 position DIP selector.  I was able to find everything either from DigiKey or on eBay.  One suggestion....before you remove the trim pots take a reading on them so you can adjust the new ones (if you plan to replace them too) to the same value.  I neglected to do this with mine and now don't know what they should be set at.  This could possibility be part of the problem I'm having with the card not recognizing a disk in the drive.  If you do take the reading would you let me know what it was in a post and I will set mine to the same value.  Thanks.

 

If you look at this page ...

 

[http://www.s100compu...d/ZFDC.htm#Data Seperator Adjustment] hyperlink not working - copy/paste the bit between the []'s)

 

... it has the procedure for adjusting the two pots. But you need to be able the program the FDC to a certain mode though (possibly a bit of assembly) and you'll need an oscilloscope or logic analyser. Or a trial and error approach seems possible ...


Edited by Stuart, Sat Aug 6, 2016 1:51 PM.


#104 justacruzr2 OFFLINE  

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Posted Sun Aug 7, 2016 12:27 PM

 

If you look at this page ...

 

[http://www.s100compu...d/ZFDC.htm#Data Seperator Adjustment] hyperlink not working - copy/paste the bit between the []'s)

 

... it has the procedure for adjusting the two pots. But you need to be able the program the FDC to a certain mode though (possibly a bit of assembly) and you'll need an oscilloscope or logic analyser. Or a trial and error approach seems possible ...

 

Thanks for the info.  At least I now know what these trim pots are there for.  One is a 50K pot like he uses on his board and the other is a 10K pot.  I probably shouldn't have touched these until I replaced everything else and tested it.  Only if it was still not working right should I have tried replacing these.  Not having the fancy equipment leaves me with the trial and error method or maybe I can contact Richard Bell and see if he can do the adjustment.



#105 RickyDean OFFLINE  

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Posted Mon Aug 8, 2016 6:25 AM

 

I'm assuming that means you already removed it.  No matter...also assuming that it's being supplied with 5 volts when on the board so you still should be able to see what it's allowing to get thru off the board.  The middle pin is the wiper so you want to get a reading between the 2 outer pins.  Because I'm not sure which direction voltage is being supplied to the trim pot (which outer pin...unless the trim pot has a "+" sign over one of the pins) you may have to try both ways.  Try supplying 5V to one side and take a reading on the other side.  If that doesn't work, or you get an odd reading, try reversing the test leads.  Also assuming your tester can supply 5V thru the positive lead.

 

Okay, I'll see what I can find out tonight. Thanks



#106 justacruzr2 OFFLINE  

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Posted Tue Aug 9, 2016 10:38 AM

OK...here's what I found when examining the WD2793 circuit traces on the CC9900 board and comparing them with the pinout chart and the instructions given at the web page:

http://www.s100compu...d/ZFDC.htm#Data

Pin 18 (RPW - Read Pulse Width) is tied into the 50K trim pot (W503).  This is the one he uses to adjust the 50K trim pot as mentioned in his instructions.  As viewed from the front (component) side of the board, the right pin is voltage (+), the middle pin (Wiper) is tied to pin 18 and the left pin is ground (-).

Pin 22 (TEST) is tied into the dual pin jumper that is just to the lower right side of the WD2793.  This is what he refers to as JP4 in his instructions.

Pin 29 (TG43 - Track Greater than 43) has a single pin jumper tied into it (about mid point on the right side of the WD2793).  Used to observe the continuous pulse.

Pin 33 (WPW - Write Pulse Width) is tied into the 10K trim pot (W103).  As viewed from the front (component) side of the board, the right pin is voltage (+), the middle pin (Wiper) is tied to pin 33 and the left pin is ground (-).

This is probably enough information now to be able to adjust the 50K trim pot but there's no information as to how to adjust the 10K trim pot in his article.  I did get his email address and I'm going to send him a message and ask him about this.  His board uses 2 trim pots also and maybe that 2nd one is for the Write Pulse Width.  Thanks to Stuart for hunting down the info on the 50K trim pot.



#107 Stuart OFFLINE  

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Posted Tue Aug 9, 2016 11:45 AM

The two pots also get a mention in the FDC data sheet - there's a copy at [http://lab.nethence....3 datasheet.pdf]. For the WPW, it seems a little vague as to what value you need (but reading more of the datasheet might help - I only had a very quick skim through).



#108 justacruzr2 OFFLINE  

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Posted Wed Aug 10, 2016 10:40 AM

OK.

 

The two pots also get a mention in the FDC data sheet - there's a copy at [http://lab.nethence....3 datasheet.pdf]. For the WPW, it seems a little vague as to what value you need (but reading more of the datasheet might help - I only had a very quick skim through).

 

I'm going to check that out.  Also got a reply from him.  Here's what he said:

 

It’s been a long time since I did that board and have forgotten much of the details.   I do remember that (at least for single density) the settings are really not critical.  Start with the trim in the middle of the pot and do disk reads watching for errors.  If however you have a scope you can fine tune it as I describe (referring to the 50K trim pot).   The second pot is for write pre-compensate and except for very old 8” drives can be ignored (referring to the 10K trim pot).  The WD data sheet really explains well the setup.
 

So according to what he says, the 10K trim pot for write pre-compensate is not critical.  I suppose that setting it in the middle of its range should be sufficient but I will also look at the FDC data sheet for any additional guidance.  Thanks again Stuart.



#109 RickyDean OFFLINE  

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Posted Wed Aug 10, 2016 10:49 AM

OK.

 

 

I'm going to check that out.  Also got a reply from him.  Here's what he said:

 

It’s been a long time since I did that board and have forgotten much of the details.   I do remember that (at least for single density) the settings are really not critical.  Start with the trim in the middle of the pot and do disk reads watching for errors.  If however you have a scope you can fine tune it as I describe (referring to the 50K trim pot).   The second pot is for write pre-compensate and except for very old 8” drives can be ignored (referring to the 10K trim pot).  The WD data sheet really explains well the setup.
 

So according to what he says, the 10K trim pot for write pre-compensate is not critical.  I suppose that setting it in the middle of its range should be sufficient but I will also look at the FDC data sheet for any additional guidance.  Thanks again Stuart.

I am still going to get readings from both of mine. I have ordered replacements parts from Jameco and will be rebuilding it as soon as everything shows up. I seem to have misplaced the contained\r holding the original parts though, that's why I have not yet gotten the readings :_(



#110 justacruzr2 OFFLINE  

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Posted Wed Aug 10, 2016 10:59 AM

I am still going to get readings from both of mine. I have ordered replacements parts from Jameco and will be rebuilding it as soon as everything shows up. I seem to have misplaced the contained\r holding the original parts though, that's why I have not yet gotten the readings :_(

 

Since my original reply some of the details have changed as per the above.  So be sure to use that info also.  And I have to correct myself.  When you take the readings I suggest checking between the (+) pin and the Wiper (middle pin) since it's the middle pin that's connected to pin 18 of the WD2793.  The 10K pot seems to be not critical as per above.



#111 RickyDean OFFLINE  

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Posted Fri Aug 19, 2016 6:34 AM

Okay, I am putting this puppy back together again, have completed the sockets. I will get the readings on the VR's tonight(just found the stuff, had crammed them into my parts cabinet) and post them tomorrow. I still have to order the all the little stuff.

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#112 RickyDean OFFLINE  

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Posted Mon Aug 22, 2016 6:39 AM

Okay, I am putting this puppy back together again, have completed the sockets. I will get the readings on the VR's tonight(just found the stuff, had crammed them into my parts cabinet) and post them tomorrow. I still have to order the all the little stuff.

Okay I got some readings on the to variable pots, the 50k: 3-----14.36K----2------36.8K-----1.   The 10K: 3-----1.60K----2------8.99K-----1. In the picture, the 50K is on the left. Also here are a couple of slightly better images of the card as I rebuild it.

Attached Files



#113 justacruzr2 OFFLINE  

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Posted Mon Aug 22, 2016 10:48 AM

Is the way to

 

Okay I got some readings on the to variable pots, the 50k: 3-----14.36K----2------36.8K-----1.   The 10K: 3-----1.60K----2------8.99K-----1. In the picture, the 50K is on the left. Also here are a couple of slightly better images of the card as I rebuild it.

Is this the way to read that: "between pin 3 and pin 2: 14.36K; between pin 2 and pin 1: 36.8K"?  And if so which pin are you calling pin 3?


Edited by justacruzr2, Mon Aug 22, 2016 10:49 AM.


#114 RickyDean OFFLINE  

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Posted Mon Aug 22, 2016 10:52 AM

Is the way to

 

Is this the way to read that: "between pin 3 and pin 2: 14.36K; between pin 2 and pin 1: 36.8K"?  And if so which pin are you calling pin 3?

Yes, that is the way to read it, and if you can bring up the photo full size, of the two pots, you'll find the answer to the second question. The number 3 is on the left side front face of the pot, 2 in the middle, 1 on the right.  :)



#115 RickyDean OFFLINE  

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Posted Tue Aug 23, 2016 6:13 AM

     Below is the progress that I have made so far, now I have a question on the picture that I have the areas circled in red( this card is a picture I pulled from my archives). The one next to the two eproms, mine did not have any jumpers, but in other photos, in my archives, I see jumpers in several configurations, is this why my TI kept coming up with a cyan screen, was this tear down preventable?

    The area where the trim pot is marked, what is the value on your pot, mine keeps fluctuating around?

    And what is the purpose of the two caps on the marked regulator, for decoupling or smoothing out of the by-passed voltage? I am trying one of the TRACO dc-dc converters talked about in the 1meg SAMs thread, instead of a regulator.

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#116 justacruzr2 OFFLINE  

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Posted Tue Aug 23, 2016 11:01 AM

Got it....

 

Yes, that is the way to read it, and if you can bring up the photo full size, of the two pots, you'll find the answer to the second question. The number 3 is on the left side front face of the pot, 2 in the middle, 1 on the right.  :)

Got it...Thanks.

 

"The one next to the two eproms, mine did not have any jumpers, but in other photos, in my archives, I see jumpers in several configurations, is this why my TI kept coming up with a cyan screen, was this tear down preventable?"

 

I've seen the same thing in another photo.  But mine has only 1 jumper between pins 2 and 3 on the lower 3 pin jumper pack.  Those other jumpers in other photos may be for testing purposes.  I don't know for sure.  All I can say is that my card works except that it doesn't recognize a disk in the drive.  I doubt that's the reason why.  There are still some minor unresolved issues like setting my trim pots and until I have addressed all those things I'm not pointing the finger at the jumpers.

 

"The area where the trim pot is marked, what is the value on your pot, mine keeps fluctuating around?"

 

Haven't done mine yet.  You do have to do the procedure correctly to be able to adjust it correctly.  The master Reset has to be pulsed first before you jumper the pins and put it into test mode.  The better and correct procedure is in the datasheet for the WD2793.  I downloaded it and read it and it's very thorough.  The setting that other fellow who built his own disk controller card is incorrect for 5 1/4" floppies.  He said to set the 50K pot to 250ns but he didn't mention that setting is for 8" floppies.  The datasheet says 400ns for 5 1/4's.  I recommend you download that datasheet and read it.  The procedure for setting both the 50K and 10K are there.  Afterwards they should settle down and give a steady reading.

 

"And what is the purpose of the two caps on the marked regulator, for decoupling or smoothing out of the by-passed voltage?"

 

Basically you are correct.  The answer is actually in this thread a page or 2 back.

 

Hope that helps!



#117 RickyDean OFFLINE  

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Posted Thu Apr 20, 2017 11:08 AM

Well folks, after a hiatus, I am resuming the rebuild of this Corcomp controller. I had to search google for the proper, I hope, replacements, and found most, after getting the values from Jameco and Mouser. I had to concentrate on getting my salvage diesel truck fit to be inspected for a rebuild title, so it took a lot of my time(shame that life gets in the way of a good hobby, right :_( ), as well as a couple of broken ribs.. Any way in the picture  in #79 it shows two tantalum caps, orange in color in the photo, I have seen other corcomp photos with electrolytic caps there instead, does it matter. I am good at building from kits and plans, but have never had any formal training in electrical components, so I know what can be substituted or not. Are the values the same as the other electrolytic caps, 47uf 25v, and what would be the limits, say can a  35v cap be used? Thanks for your input, and I have included a snippet. Once i get it together and working I will put together a BOM of small parts.

   

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  • Attached File  ccdc.jpg   260.38KB   0 downloads


#118 Shift838 OFFLINE  

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Posted Thu Apr 20, 2017 1:33 PM

Well folks, after a hiatus, I am resuming the rebuild of this Corcomp controller. I had to search google for the proper, I hope, replacements, and found most, after getting the values from Jameco and Mouser. I had to concentrate on getting my salvage diesel truck fit to be inspected for a rebuild title, so it took a lot of my time(shame that life gets in the way of a good hobby, right :_( ), as well as a couple of broken ribs.. Any way in the picture  in #79 it shows two tantalum caps, orange in color in the photo, I have seen other corcomp photos with electrolytic caps there instead, does it matter. I am good at building from kits and plans, but have never had any formal training in electrical components, so I know what can be substituted or not. Are the values the same as the other electrolytic caps, 47uf 25v, and what would be the limits, say can a  35v cap be used? Thanks for your input, and I have included a snippet. Once i get it together and working I will put together a BOM of small parts.

   

 

 

This chart works good to convert capacitor values.  I have used it many times when upgrading/repairing PEB cards and musical equipment.

 

HERE

 

Also, 35v will work in place of the 25v with no issues.  It's increases the max voltage it can take.  I typically replace and use 35v in all my peb cards.






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