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Corcomp 9900 disk controller problems

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This card has been operating fine up til a couple days ago. Now the LED light on the card stays illuminated and the attached floppies are not accessible. All the usual tricks didnt rectify it.. I even plugged it into a different empty PEB and had the same results. Everything physically looks fine on the card. What is a good starting place for getting this functional again? I was thinking about replacing the TMS 9901 chip for starters.

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Start with the buffers. They'll normally be at the bottom of the board, next to the edge connector. I'm assuming of course that it has buffer chips!

 

Also, the voltage regulators. Lastly, any "can" type capacitors should be changed. 30 year old electrolytic capacitors are going to be way off spec by now. I see this in guitar amplifiers and vintage guitar effect pedals all the time!

 

There's probably not much wrong with it at all.

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The 9901 IS the buffer on the CorComp card. . .that particular design flaw was the demise of many a CorComp card in the past. Easy enough to fix if you have some spare 9901s, but more expensive than fixing the buffer chips used on other boards.

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Maybe it's about time to design an FPGA emulation of a 9901? :)

If its pin compatible, way to go, I'd like to see replacements for all the major chips on all of my boards. I just found and bought some SMC hdc chips for my HFDC's from various countries, and would like a source for replacement gate arrays if the logic is available to burn them. As money permits I am trying to get working replacements, just in case. After the first of the year I will be buying a better eprommer.

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The 9901 IS the buffer on the CorComp card. . .that particular design flaw was the demise of many a CorComp card in the past. Easy enough to fix if you have some spare 9901s, but more expensive than fixing the buffer chips used on other boards.

 

Guess I will start with that and go from there. I have a couple spare CC RS232/PIO cards which I should be able to pull a 9901 from.

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Hmm well scratch that idea. The two CC cards I have both are the type with serial port jumpers, so neither have a 9901. One has an AMI8524 and the other an AMI8327. What's a good online source for a quality 9901?

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That's a good price for them too--it is about the same price as I paid for each of the chips in the last group of 20 that I bought. . .

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Hey guys, got ahold of a few 9901s (thanks Willsy!), and replacing it did the trick, so the controller is back in business.

 

Yeah! Great job!

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Hey Guys, I have a Corcomp, that will work ok with a Geneve, but when it is turned on with a TI, the system locks and stays on the Title screen. I have changed, moved, or tested all of the logic chips on the board to no avail. Does anyone know of anything specific to the TI on the card that the Geneve doesn't need. The eproms are the MIller Graphic eproms and I don't have a way currently to test them. On a side note, last night I finally got my TI to format a MFM hard drive....Yes! I'm getting there slowly.

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If it works on the Geneve but it doesn't work on the TI, that is a sure-fire pointer to the DSR being corrupt or not being read properly. The Geneve uses its own Master DSR to access the card and ignores the one on the card, which is why it works with the Geneve. . .and fails on the TI.

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If it works on the Geneve but it doesn't work on the TI, that is a sure-fire pointer to the DSR being corrupt or not being read properly. The Geneve uses its own Master DSR to access the card and ignores the one on the card, which is why it works with the Geneve. . .and fails on the TI.

That's what I was figuring, but I was hoping that it might turn out to be something else like a bad transistor. All the logic chips that my old tester could test showed up as good.

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If you've got a MiniMem cartridge you can use EasyBug to 'switch the card on' and check you can read the DSR. There's details on a thread somewhere ...

 

Edit: Take a look at this post: http://atariage.com/forums/topic/227990-ti-99-disk-controller-question/?hl=%2Beasybug&do=findComment&comment=3039394 If the first 2 bytes at >4000 aren't AA 00 then there's a problem reading the DSR. Assuming you've got a MiniMem cartridge to hand of course, and the CorComp card resides at CRU address >1100. You'd need to look at further bytes to completely confirm, but you'd need a dump of the EPROMs to compare against.

Edited by Stuart
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If it works on the Geneve but it doesn't work on the TI, that is a sure-fire pointer to the DSR being corrupt or not being read properly. The Geneve uses its own Master DSR to access the card and ignores the one on the card, which is why it works with the Geneve. . .and fails on the TI.

 

So how does the master DSR business work? Does it 'know' about all the cards you're likely to fit in the PEB, or work in some other way?

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If you've got a MiniMem cartridge you can use EasyBug to 'switch the card on' and check you can read the DSR. There's details on a thread somewhere ...

 

Edit: Take a look at this post: http://atariage.com/forums/topic/227990-ti-99-disk-controller-question/?hl=%2Beasybug&do=findComment&comment=3039394 If the first 2 bytes at >4000 aren't AA 00 then there's a problem reading the DSR. Assuming you've got a MiniMem cartridge to hand of course, and the CorComp card resides at CRU address >1100. You'd need to look at further bytes to completely confirm, but you'd need a dump of the EPROMs to compare against.

Yeh, I remember seeing that some time back, but the problem is as I turn on the system it locks. Now to be honest, I just realized that I am using a Corcomp Ramdisk at the same time, so I will take it out and try the rig. But the Ramdisk, or at least the 32k memory part of it works fine(tested with the Corcomp diagnostic cartridge), and the Call RAMGR function in its DSR is good, and I just formatted a MFM drive on the TI rig I am using with a HFDC installed, so I assume it's good. I was thinking maybe that either a PAL chip on Corcomp controller could be a problem or there are two chips, the MCM2114P SRAM and RCA CD4069UBE CMOS Hex inverter(don't know any thing about these chips), that I thought could be a problem. Or the 74LS123 chip(My tester does not have a listing for these and cannot identify it when it is plugged into the socket), but I haven't been able to search for a spare yet. Since I got my HFDC functional a couple of weeks ago, its priority has fallen. Still working on my cars till 9 or 10 at night, after work.

Edited by RickyDean

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The Master DSR has the code to run things like Hard Disks, Floppy Disks, RS-232 cards, and (IIRC) Horizon RAM Disks as the hooks for these things are in the Master DSR. That is why the CorComp disk controller will read and format 80-track disks in a Geneve. . .

 

Other things using DSR space are not supported by the Master DSR. ROMPAGE allows you to bypass the Master and use the DSRs on individual cards. . .

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If it works on the Geneve but it doesn't work on the TI, that is a sure-fire pointer to the DSR being corrupt or not being read properly. The Geneve uses its own Master DSR to access the card and ignores the one on the card, which is why it works with the Geneve. . .and fails on the TI.

 

You may need to put in new eproms since the Geneve bypasses the cards DSR.

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You may need to put in new eproms since the Geneve bypasses the cards DSR.

That may be, but why would a eprom die if it has not been electrically connected for 17+ years and all the surrounding logic checks good, and the erasure window has been covered the whole time? Just a question that may not be able to be answered to well, but I would almost have to rule out static as a culprit since other cards packed with it are working okay. If I remember correctly it was fully functional when packed away. Any how if I can get my Mechatronics programmer to function I can try to program another set of eproms or if I can get my old Logical Devices Gangpro 8( need 1980's software, I believe) to function on a old PC, I could use that. Anybody got the old software for it? I have searched all over with google and other engines to search, but can't seem to find it.

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I read the manual and it said that there were two versions of the software, one for the older model and one for the newer one. It might just work, as I found references to the same software being used back as far as 2004. . .

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I read the manual and it said that there were two versions of the software, one for the older model and one for the newer one. It might just work, as I found references to the same software being used back as far as 2004. . .

Okay, I've downloaded it and will try it over the weekend, I still have a system that runs winXP. I think in my group of stuff, I should have some eproms that will work.

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