CorComp 9900 DSDD disk controller

[johnph3]

I recently acquired a Corcomp 9900 disk controller card for the PEB. Looks to be modified for it has a daughter board with a WD1773 28 pin controller chip plugged into the original 40 pin socket on the main board. My question is what was original 40 pin controller chip and can I replace the daughter board with the correct 40 pin chip? Thanks for your help

[+dhe]

Pictures would be great. The is a thread here not to long ago which I think applies to your board.

The original chip used in the corcomp was very buggy, the daughter-board is an engineering fix for reliability.

 

Is the unit working?

[+mizapf]

Corcomp FDC with WD1773 and with WD2793

[+Ksarul]

The board you have is the original revision of the CorComp DSDD controller. It was designed for the WD2793 controller chip. Unfortunately, at the time CorComp started production on them, a huge number of defective WD2793 chips were released into the distribution channel by the manufacturer. The defect was due to a process error at the factory. The defective chips affected a lot of OEMs at the time, as the 2793 was a pretty popular chip. There was a serious uproar about it in the tech media at the time.

 

Some chips produced at that time were good, but something like 90% of them from the affected lots were bad. CorComp tested their on-hand stock and fitted the good ones into as many of the disk controllers from the first run as they could. There weren't anywhere near enough good chips though, so they built the daughter boards with the software-compatible WD1773 on them and finished the run. To avoid a repeat of the problem, the boards were redesigned to use the WD1773 from that point on. If the board you bought was the one recently sold on eBay, I believe it even included a letter from CorComp that somewhat explains what they did (a clean scan of that letter would be a good thing to add to our online documentation repository too). Your DSDD controller with the daughter board is actually seriously uncommon, so you may want to keep it as it is.

[johnph3]

so mine looks like bottom production board except instead of 40 pin chip it has this daughter board with wd1773 on it. So my question is is there any other mods done to the main board to allow the daughter board to work. The daughter board is built on a 40 pin plug that plugs directly onto the main board 40 pin socket. I read about the issue at the time, but I was wondering if I came across a new version of the WD2793 which is what I believe is original could I substitute it without any reverse modification? Just like to play you know.

[apersson850]

I have one of those with a working 2793 controller.

[johnph3]

It is working in it's current configuration. So you might wonder why I want to mess with it? Because I can,  I like to play and see if I can get it to work as originally designed. Strange thing I have noticed going between it and my ti floppy controller is the ti controller doesn't recognize the disk I formatted with the CorComp controller not even the single density ones. However the Corcomp seems to functiopn properly, haven't had any trouble formatting disk single density or double density and it reads back fine. I did however burn a couple of upgrade proms for it to get rid of corcomp's annoying opening screen.

[+arcadeshopper]

55 minutes ago, johnph3 said:

It is working in it's current configuration. So you might wonder why I want to mess with it? Because I can,  I like to play and see if I can get it to work as originally designed. Strange thing I have noticed going between it and my ti floppy controller is the ti controller doesn't recognize the disk I formatted with the CorComp controller not even the single density ones. However the Corcomp seems to functiopn properly, haven't had any trouble formatting disk single density or double density and it reads back fine. I did however burn a couple of upgrade proms for it to get rid of corcomp's annoying opening screen.

it also won't read a disk formatted dsdd with my corcomp controller right?  maybe some sort of issue with either your drive or that controller 

 

Greg 

[johnph3]

This my Corcomp 9900 card. IT is working and is capable of formatting  double density disk and reading from them. And I have tried three different 5 1/4 inch half height drives A teac fd235 and a panasonic JU-475. The other one however is not double density but these two are. Same issue reading the tunnels of doom disk. I don't know why.

[atrax27407]

FWIW, Unicorn Electronics has 2793 disk controller chips for $14.99. Their stuff is really good.

[johnph3]

23 hours ago, arcadeshopper said:

it also won't read a disk formatted dsdd with my corcomp controller right?  maybe some sort of issue with either your drive or that controller 

 

Greg 

It reads the header and catalogs part of contents but not all of it

[+arcadeshopper]

14 minutes ago, johnph3 said:

It reads the header and catalogs part of contents but not all of it

sounds a lot like it's not reading side 2.

[+mizapf]

If you have the Disk Manager cartridge or some other disk manager tool, try to do a sector read over all sectors of the disk (simple test). Note the first sector that is unreadable.

 

For instance, when there is a problem with the second side, you should be able to read sectors 0-719 of a DSDD disk, but sectors 720-1439 are unreadable.