Mix Computer Trouble Shooting

[alchematic]

When my TR computer went south I sent it to Bruce Millet who did a rebuild and test for a reasonable price though I don't remember what the price actually was. He is a great guy and very very helpful!!

I had a really hard to track down problem  ..  no booting or operating of the computer that was caused by this. If you have replaced screws in the rack side, you can install one that is slightly too long and it will connect to the buss and/ or crush an unused connector. Mine was on the upper left top connector. This pulled a couple buss lines down with out either frying anything of screwing up power rails. I can't even tell ya how much fun it was figuring that out!

[sintech]

Got Marc’s CA floppy card to boot in the test computer.. which is just a load of spares that have never worked together, so hard to know what's good or not…



Whatever the order of the cards, can never got the keyboard to work, yet.. could hear it beep back to warn me that a Reel Disc wasn’t inserted.

The bus driver is kind of doing this!!.. https://www.youtube.com/watch?v=3-JVOvR7LZM&feature=youtu.be

When tested in the studio computer, get the red light also.. and it seems fine, but I didn't have the console on for that test. Normal operation is just the yellow LED.

CA Floppy card tested in the known working Studio machine.. gives the same result, as the test computer.. boots, but keyboard doesn’t react, so this is definitely bad

[marcmozart]

Thanks mate! We're getting there Andy!!

[Artur D'Assumpção]

Andy,

Thanks so much for the troubleshooting! This is been the computer troubleshoot from hell! I feel for Marc...

And I promise I will cry when Marc gets his computer back to life!

You know what I say? Lets get the SSLMixed Computer running and you'll shed no tears anymore!

Cheers,

Artur

[glorymorris]

I'm having a similar issue with our G Computer -- The garbled screen, no disc access. We actually have two computers-- just received one from a guy in Germany. It was supposed to be totally working, but it didn't even come with the original floppy drives.

Our main mix computer has these aftermarket cards by the Desk Doctor. They're for G+ SCSI floppies, presumably to mate with a G computer. I'm kind of confused by these two computers which are externally ostensibly the same. Their cards are quite different. The BUS driver in the computer we just received doesn't have pushbutton switches like the other one.

Anyway-- no disc access occurs. The drives power up fine, but no action. Screen hangs on the garbled mess for a second, then clears and goes blank. Any tips would be appreciated.

[glorymorris]

Actually, upon further inspection it appears the primary differences are in the total recall outfitting. Our original motherboard seems to have been modified to go along with the new cards provided by Desk Doctor for connection to G+ Floppy Drive systems. It contains a different Autoload Rom chip .

If I had the original G floppy drives, it might boot up correctly.

[sintech]

You need to workout what processors are in the two computers. If you have aftermarket cards to run G+ 3.5" then the CPU is most likely to be a 490.

The G from Germany, maybe a standard 4100/A

[glorymorris]

You need to workout what processors are in the two computers. If you have aftermarket cards to run G+ 3.5" then the CPU is most likely to be a 490.

The G from Germany, maybe a standard 4100/A

This is true. I don't really have any information pertaining to the main computer card. I purchased a G Service Manual from a link here in the forum, but it contains very "light" functional descriptions of the independent subboards and literally no information about the motherboard.

[glorymorris]

One of the cards reads 'LSI 4/95 BASIC' -- this is the one modified by Desk Doctor.

The other has no marking that I can find (this is the one from Germany)

[sintech]

If you can take some pics.

[glorymorris]

If you can take some pics.

I'm pretty sure these two boards are 4/90 boards. I dug out a 4/100 board from our supplies and compared all 3. They appear to be almost completely 74 Series logic. From what I've extrapolated, one of the processors has a special AutoLoad ROM chip and mates with two other cards designed to trick it into working with the G+ 3.5" Floppy drives.

Swapping the ROM chip to the other motherboard, swapping out motherboards, etc has done nothing to change the fact that the screen loads up gibberish and appears to wait for data to load into memory from some medium. It's a shame the guy we bought this spare computer from didn't include the drives.

I don't have my Logic Analyzer on me, otherwise I could take a peek at what's happening on the busses. Looks like I need to call Desk Doctor...

[marcmozart]

As Andy said, pics would be appreciated. Andy and I have most of the CPU-cards that were made around, so we can quickly compare.

[ULH]

Sorry to dig up this old thread but I have a question related to all the 4/30, 4/90 and 4/100 processor and memory talk:

In the "SSL Setup page" (see G computer service manual section 1 page 11) there is a setting called "Processor/Memory Type". The manual says this setting should always be set to "1" and states "don't ask why". But I just came across setting up a computer where this setting needs to be "2" to make it read from the reel disk. It will boot and function in the "1"-setting but without any access to the reel floppy which of cause is of no use. Is it because the cpu board in this computer isn't the G type 4/100 but maybe an 4/30 or 4/90? I havn't checked on the physical pcb yet.

This is the g4.01 software connected to a 4000e vca console.

What does this setting do?

Cheers,
Uffe