Mix Computer Trouble Shooting

[marcmozart]

Starting this new thread as I'm currently troubleshooting the Mix Computer.

Check the "Rebirth of the Mix Computer" for details of cleaning/refurbishing the beast!
http://forum.sslmixed.com/index.php?topic=499.0

[marcmozart]

I got a 490 card (E-Series) in this computer with the earlier (standard) memory.
There's a CA Floppy Controller Card to connect the computer to the 8" Floppy Drives.
All the other components + the rack case are from a 1991 G-Computer.

When I switch the power supply on, I get the (totally normal) scrambled screen on the Consoles VDU.
Upon switching the "Solid State Logic"-logo on the the Dual Floppy Drive, nothing happens though. The Floppy drive with the program disc (with a red "P" on the front panel of the Floppy Drive) shows the red activity LED, but the system does not boot.
There is of course a working 8" Floppy (with E-Series System Software) in the drive.

Any ideas?

[marcmozart]

OK, here we go - the actual troubleshooting begins. I am trying 3 different CPUs (2x 4/30 E-Series, 1x 4/90 E-Series) with the standard memory module to see if anything changes.

These are the 2x 4/30 CPUs:



When I switch the computer on, I am getting the following pictures on the VDU - here's one picture for each installed CPU:







Fairly consistent result, I would say. The letters on the screen are almost the same on all three CPUs, with a few different ones.

[marcmozart]

I hope anybody with knowledge of the mix computer can chime in at one point. My problem is, I'm getting the "scrambled screen" upon switching the computer on, but the connected 8" Floppy Drive does not boot (after pressing the "Solid State Logic-Logo"-button on the 8" Drive. The drives are spinning, but the heads never try to access anything, I can never hear the heads of the Floppy Drive.

Here are the next steps I'm going to try - these are suggestings from other forum members that I've spoken to in the last couple of days:

- Lower row of cards have to be installed in the right order.

- Lower row of cards should all be connected to the computer interface card (the card in the back door of the computer).

- Tape Machine Interface needs to have fresh batteries.

- Measure voltages of power supply.

- Check LEDs on Bus Driver Card (anybody knows what these mean?).

- Test all involved ribbon cables.

- Try a different Floppy Disc Controller Card (could be defective and not sending anything to the Floppy Drive).

Since I've tested 3 different CPU/Memory-Combinations, and getting consistent results, I am ruling out the CPU/Memory as the problem for now.

I'd be grateful for any input and/or help!!!

[sintech]

This is the boot sequence of my machine, 4100/A CPU, My "Solid State Logic-Logo" button is broken.. so it starts without activating this, need to investigate if this contact has been jumpered.

https://www.youtube.com/watch?v=9y220c59Jhs&list=UU4h-bJXCVct3T-WrPx4NwXw

[jimlfixit]

Hi chaps
I remember those old large computer cards and I'm surprised they are still just about working today.

I guess cleaning the edge connectors (Marc is probably an expert in this) and inspecting the cards for dry joints has been done (30 years is a long time). Both cards seem to produce the same scrambled results on the screen so it has to be another problem.

Also, Marc has cleaned his computer rack but, I must say that, a lot of the problems with SSL's these days (apart from changing components) seem to be related to the connectors from what I have read on here. So often, I read that, taking out a card or connector, giving it a clean and putting it back, seems to work.

It's a bit like your modern day computer, tablet or phone when it doesn't connect to anything else for some reason. Apart from component failure, it just could be a case of cleaning the connection and putting it back.

Just a thought and hope it helps. Meanwhile, roll on the replacement computer system chaps as I'm sure everyone will have far less hassle in future if it happened.

Regards from Jim Lassen

[StefanNowak]

Bruce Millett knows everything.

[waltzingbear]

You are in a very bad place for troubleshooting. None of this system can be said to be known working as it has been disassembled, reworked and reassembled recently.

You need a working computer to start making headway. Substitution into a known working system of the cards one by one is the best way to begin proceeding. Then you can have a smaller number of problems to pursue. Do you really even know if the disc you are attempting to use is in good shape? I have seen similar results from a bad disc.

Without reducing the number of potential problems, you could be chasing your tail for a while.

Alan

[Artur D'Assumpção]

Hi Marc,

We've been talking a lot about this and going through several hypothesis and procedures. At this stage I would go through the following steps:

My 5cents would go to the floppy controller or the floppy drive. With this said, and to rule out all stuff before sourcing these parts, I would also try the following things:

- Do a continuity test all important ribbon cables with a multimeter. Many times plugin and unplugging these cables some bus lines can be broken. Also it's often that the plugs on these cables get bad connections.  So I would go through these 1st...

- Since the Tape card should be connected to boot the computer, I would also replace all the dried batteries, just to make sure this card is working correctly.

- Make sure all the ribbon cables for the lower cards are connected to the Computer I/F card. I'm not sure of this, but this can actually make some interconnections between the cards and the computer that can be important to properly boot:



- If the drive's not spinning but it's lighting, sometimes this happens because the drive is missing one voltage to the motors. This often is a problem with bad connections. I would check with a multimeter if all voltages are present.

- Is the drive trying to read the disk and making the noise, like the one in Sintech's video? If so, the reading head of the drive could also be dirty and needs to be cleaned.

Cheers,

Artur

[StefanNowak]

I'm not sure the Tape card needs to be in there.

I took mine out for a while.

[michaeldtech]

Try to boot by pushing and holding both switches on the bus driver.  From ancient memory, you hold both until the LED's change state then release and check that the yellow (i think) is flashing indicating data from the floppy.  It should flash while booting and then the green goes solid.  A solid red light is not a good thing.  Again, totally from memory have not done this in over 12 years.

I would do this with the I/O cards, TR, Tape, etc unplugged and only the CPU, bus, floppy, keyboard cards plugged.  It should boot partially and then indicate that hardware is missing.

Have you verified all voltages from the supply?  You can do that from the solder side of the motherboard.
Mike

[Artur D'Assumpção]

I'm not sure the Tape card needs to be in there.

I took mine out for a while.

I'm just recalling from documentation. If someone can test this out on a working computer and checks out then Marc can totally remove this card for troubleshooting purposes. When troubleshooting less variables is better!

[Artur D'Assumpção]

Try to boot by pushing and holding both switches on the bus driver.  From ancient memory, you hold both until the LED's change state then release and check that the yellow (i think) is flashing indicating data from the floppy.  It should flash while booting and then the green goes solid.  A solid red light is not a good thing.  Again, totally from memory have not done this in over 12 years.

I would do this with the I/O cards, TR, Tape, etc unplugged and only the CPU, bus, floppy, keyboard cards plugged.  It should boot partially and then indicate that hardware is missing.

Have you verified all voltages from the supply?  You can do that from the solder side of the motherboard.
Mike

This is very good info! One of the things I've learned is that the leds on the bus driver card (i think) actually give you some troubleshooting info, but I've found hard to get any info on how to decode/troubleshoot these. Do you have any info on this?

Cheers,

Artur

[sintech]

Tying to understand more of the computer side of things, as my last computer worked flawlessly for seven years it was with me.. great reliability, but not so great for the learning curve.

Regarding Computer PSU rails, could anyone explain the principles of the 5v Hang Regulator?

[marcmozart]

OK I got some news.

I've exchanged a few e-mails with Werner (the designer of the "The Konnektor" Sync Box), who is probably one of the most knowledgable people about this computer.
Here's what he says:

1. The "scrambled screen" is produced by the VDU & Keyboard Card. The screens I'm getting at start are not related to the CPU at all. In fact, I've took the CPU out, and I'm getting the same exact "scrambled screen". It could be that the computer hangs at this graphic, so trying to reseat the graphics card and the ICs helps sometimes. (Tried that, no luck!)

2. Tape Machine Interface is not needed to boot the computer. So I'm taking it out until we got the computer to boot.

3. The CPU needs to have a working Autoload-ROM. It's a chip on the CPU that tells the CPU what device to boot from. Back in the day, you could boot it from a paper card or Tape or Floppy.
The 3 CPUs I have here, have the number 682-38 handwritten or printed on the Autoload-ROM. Werner says that he never got his computer to boot from Floppy when using the Autoload-ROM with this exact number. He is using an Autoload-ROM with the number 683-38. Plan is to clone the Autoload-ROM that works on Werner's computer.

Will try some things and keep you updated.