Help Troubleshooting & Repairing TI FDC and TI 32K MEM cards.

[Diecrusher]

Well, my restoration of a basket-case PEB is almost finished but 2 casualties of its former bad life in a damp cellar were the TI FDC card and 32k Mem card.

 

The metal clamshell cases on both cards were heavily oxidized with most of the paint flaking off but the cards themselves looked in great shape. Now in their repainted shells they look like new but aren't working so the battle isn't over.

 

The farthest I have gone in troubleshooting is checking the voltage regulators on the cards and the voltages at the FDC chip and some of the other chips and everything looks right on so far.

 

I have tried another set of cards in the PEB and they function fine so I know that it is the cards that are bad and not the PEB itself.

 

I've tried to dig online but have come up empty so far. I would really like to fix these even if it is only for the experience of trying to resurrect them.

 

I haven't tried swapping out the FDC chip which is probably the first thing I should try since it is socketed but I am lost after that.

 

Thanks in advance for any insights...............

Edited April 6, 2015 by Diecrusher

[+Ksarul]

I may have the TI internal troubleshooting guides for both of these cards around here somewhere--I may have even scanned them and put them up on WHT at some point. I'll have to take a look and see what I've got and I'll get some scans to you if I have anything useful.

[Diecrusher]

Thank you!

 

Hopefully this stuff gets to live again!

[Fritz442]

I have repaired 3 floppy controller cards and 1 mem card.

All 3 floppy cards were 3 diff problems, but that large FDC chip

was not the issue on any of mine.

 

The mem card had 1 bad ram chip.

 

On the floppy controller, does it power on(light flash), does it come on when

accessing the drive? Same on mem card, and does it show with SIZE command.

Explain what your does exactly and maybe we can lead you in a direction.

 

And Ksarul, I would love to see a troubleshooting guide for these...

 

Fritz

Edited April 8, 2015 by Fritz442

[Gazoo]

I have repaired 3 floppy controller cards and 1 mem card.

All 3 floppy cards were 3 diff problems, but that large FDC chip

was not the issue on any of mine.

 

The mem card had 1 bad ram chip.

 

On the floppy controller, does it power on(light flash), does it come on when

accessing the drive? Same on mem card, and does it show with SIZE command.

Explain what your does exactly and maybe we can lead you in a direction.

 

And Ksarul, I would love to see a troubleshooting guide for these...

 

Fritz

 

Fritz, you are hereby elevated to the level of TI Guru.

Several things you've done recently (one of them hacking a piece of my software, much to my chagrin) have been really impressive.

Keep at it, just stay away from my stuff please.

 

Thank you,

 

Gazoo

[Stuart]

On the FDC, I'll put my money on the 74LS245 data buffer being bad.

 

Have you got a Minimem cartridge? You can use that to switch on the card by writing a 1 to CRU address >1100, which should light the LED on the front of the card. Next look at memory locations >4000 onwards which should be the DSR on the card (starts >AA, >55 ISTR - someone with a card handy would need to check to be sure). That will prove that a lot of the card is working.

[Diecrusher]

Unfortunately I haven't' yet picked up a Minimem cartridge but it is on my wish list.

 

On first power on the FDC indicator light does flash for a sec but then the whole card acts dead. Same for the 32K card but then if I remember correctly the system locks up with garbled characters.

 

I have never done and i.c. level troubleshooting other that checking voltages. I do have a logic probe and scope though I barely know how to switch them on.

 

I looking forward to at least tinkering with this and hopefully it will be a learning experience and I might even increase my knowledge a bit.

 

Will update when I can.

 

Thanks again all.

[Fritz442]

Fritz, you are hereby elevated to the level of TI Guru.

Several things you've done recently (one of them hacking a piece of my software, much to my chagrin) have been really impressive.

Keep at it, just stay away from my stuff please.

 

Thank you,

 

Gazoo

 

Thanks Gazoo,

This means a lot coming from you, and I will only hack your stuff with your permission....LOL

 

 

Diecrusher:

A volt/ohm meter is really all you may need for diagnostics, but the logic probe is very handy.

I would first start diag with the FDC card, but install your known good mem card with it

so as to not mix issues.

Use the Disk manager cart to test you FDC, for the error messages. I assume you have only

1 drive connected? Insert a known good formatted floppy and use 'Catalog disk' - check this:

1 Does the light on the controller light at all?

2 Does the light on the drive light at all?

3 Do you hear a loud click & the disk spin... or not.(this is easier to hear with the older drives)

These are 2 separate circuits we need to know if either are active before going inside the card.

And what error message do you get.

 

Do try to get a Minimem Cart, as this will make diagnosing the MEM cart a lot easier.

Edited April 8, 2015 by Fritz442

[Stuart]

Assuming you have an E/A cartridge, the following will let you read the first couple of bytes of the FDC DSR, to test that that section of the circuit is working. Short enough to type in. Make sure you've got a GOOD 32K RAM fitted when doing this!

 

10CALL INIT

20CALL LOAD(12288,2,12,17,0,29,0,200,32,64,0,48,32,200,32,64,2,48,34,4,91)

30CALL LOAD(8234,63,48)

40CALL LOAD(16176,70,68,67,32,32,32,48,0)

50CALL LINK(“FDC”)

60CALL PEEK(12320,A,B)
70PRINT A
80PRINT B

 

If the DSR can be read, it should print the values 170 and 2 (>AA, >02 - the first two bytes of the TI FDC DSR).

 

[Opry99er]

^^That's cool!!

[Stuart]

Assuming you have an E/A cartridge, the following will let you read the first couple of bytes of the FDC DSR, to test that that section of the circuit is working. Short enough to type in. Make sure you've got a GOOD 32K RAM fitted when doing this!

 

10CALL INIT

20CALL LOAD(12288,2,12,17,0,29,0,200,32,64,0,48,32,200,32,64,2,48,34,4,91)

30CALL LOAD(8234,63,48)

40CALL LOAD(16176,70,68,67,32,32,32,48,0)

50CALL LINK(“FDC”)

60CALL PEEK(12320,A,B)

70PRINT A

80PRINT B

 

If the DSR can be read, it should print the values 170 and 2 (>AA, >02 - the first two bytes of the TI FDC DSR).

 

 

Just adding how this program works. (Really annoying that you can't edit your own posts!)

 

Line 20 pokes into memory the code for the following, starting at address >3000:

 

LI R12,>1100 'CRU base address for FDC card.

SBO 0 'Switch on card.

MOV @>4000,@>3020 'Copy word from DSR ROM at >4000 and store at >3020.

MOV @>4002,@>3022 'Copy word from DSR ROM at >4002 and store at >3022.

B *R11 'Return.

 

Line 30 changes the pointer at >202A to >3F30 to add an extra entry to the REF/DEF table. See the bottom half of page 276 of the E/A manual for further details.

 

Line 40 adds the program name "FDC<space><space><space>" and start address >3000 in the new entry in the REF/DEF table. See page 276 of the E/A manual again.

 

Line 50 calls the code just poked into memory.

 

Line 60 gets the values copied from the DSR ROM to memory at >3020 and >3021. (I've just realised that the code above is copying 4 bytes, whereas only meant to copy 2!) Found (on Classic99 at least) that CALL PEEK can't read from the DSR ROM directly as for some reason the routine is first switching the card off, hence the need for the code above to copy the bytes we need to another location, then the CALL PEEK can read them from there.

[Diecrusher]

Well an update on the FDC troubles.

 

I socketed and replaced the 74LS245 since it seemed easy to do. But problems still persist.

 

I hooked up my system with a known working TI FDC and everything works great.

 

Replaced the working card with the troubled card and have the following symptoms:

 

1. On boot screen hangs on a blank blue screen with no further option.

2. Flex-card light stays constantly lit.

3. Mem Card light blinks quickly and consistently.

 

So obviously the problem(s) still persist.

 

One other thing that I noticed was that the SN74LS161AN chip (located @ U10 I believe), had all of its legs slightly discolored brown-ish so I guessed that it may be bad? I dunno but it seems easy to replace but it is a total stab in the dark.

 

The search continues..............

Edited April 10, 2015 by Diecrusher

[Opry99er]

That's s crazy one... Sounds like your edge connectors are bad... I am certainly no expert, but for the card to hang your operation and affect other cards, I would say it sounds "short"y.

 

Good luck... I know there are some good hardware guys on here who may be able to help you diagnose.

[Omega-TI]

That's s crazy one... Sounds like your edge connectors are bad... I am certainly no expert, but for the card to hang your operation and affect other cards, I would say it sounds "short"y.

 

Good luck... I know there are some good hardware guys on here who may be able to help you diagnose.

 

Nothing more tedious and time consuming than having to pull out the logic probe and truth tables... ugh! I'd rather buy a new one!

[Stuart]

Well an update on the FDC troubles.

 

I socketed and replaced the 74LS245 since it seemed easy to do. But problems still persist.

 

I hooked up my system with a known working TI FDC and everything works great.

 

Replaced the working card with the troubled card and have the following symptoms:

 

1. On boot screen hangs on a blank blue screen with no further option.

2. Flex-card light stays constantly lit.

3. Mem Card light blinks quickly and consistently.

 

So obviously the problem(s) still persist.

 

One other thing that I noticed was that the SN74LS161AN chip (located @ U10 I believe), had all of its legs slightly discolored brown-ish so I guessed that it may be bad? I dunno but it seems easy to replace but it is a total stab in the dark.

 

The search continues..............

 

Try also replacing the 74LS125 next to the '245. This controls the READY output (amongst others) and on my FDC this was shorting READY to ground, hence hanging the console. [http://www.avjd51.dsl.pipex.com/ti/ti.htm#resurrecting_disk_system]

[Stuart]

Also see what happens if you fit the card with the new 74LS245 removed. Does the console then boot? That might point to a problem with the EPROMs, and the console is reading code that is sending it to never-never land.

[Diecrusher]

Well, today I socketed the 74LS245, 74LS161 and 74LS125 and replaced all 3 with new chips. Still boots to a locked blank blue screen.

 

I also chanced changing my EPROMs to my new 80-track ones and figured (hopefully right) that I would have nothing to lose - same result. I then pulled the 74LS245 per Stuarts advice and the machine booted fine.

 

I usually do a fine job of soldering-in sockets but I am wondering if I missed something somewhere. I even used high-quality machined ones and I am almost certain that I didn't

short any of the legs but maybe I should redo them just to be sure.

[Stuart]

Have you got an E/A cartridge?

 

Try switching the console with E/A cartridge on first so it boots, then switch on the PEB. Then try my BASIC program above. Type in and try running just line 10 first - it *may* not work (and would save you some typing) - not sure if the E/A cartridge has to be able to detect the 32K memory at power up in order for it to run CALL INIT.

[+Lee Stewart]

Have you got an E/A cartridge?

 

Try switching the console with E/A cartridge on first so it boots, then switch on the PEB. Then try my BASIC program above. Type in and try running just line 10 first - it *may* not work (and would save you some typing) - not sure if the E/A cartridge has to be able to detect the 32K memory at power up in order for it to run CALL INIT.

 

The E/A cartridge does, indeed, need to find the 32KiB memory.

 

...lee

[Stuart]

Thanks Lee.

 

Without a Minimem cartridge, that rather puts a spanner in the works trying to confirm how the DSR is reading. Although with the 74LS245 now in a socket, you could I suppose bend out the /EN pin and connect it to it's driving signal via a switch, and a pull-up resistor to +5V. Could then disable it until after power up.

[Diecrusher]

Well, further on with my feeble attempts to try to make sense of this all.

 

I pulled the the FD controller chip and tried it in a known working card and it works fine so I guess that rules out that chip being bad.

 

One other thing I noticed is that the 74LS38 @ U14 is piggy-backed on top of another chip. I dunno if this was on purpose or to repair a previous bad chip.

As I said all of this is way beyond me at my current electronics knowledge stage!

 

I will try to source and purchase a Minimem card as suggested.

 

Thanks again Stuart and all those others offering help, I really appreciate it and hope to learn something along the way.

 

Any other suggestions at all please shoot them my way.

 

Update: I just read on T. Nouspikel's site that the piggy-backed 74LS38 has been observed on other cards and may be a normal occurence. ???

Edited April 14, 2015 by Diecrusher

[Opry99er]

DieCrusher:

 

I am not using my MiniMemory currently. If you need to borrow it for some testing, I would be happy to loan it to you temporarily.

 

That is, unless you're planning to buy one for your collection anyway.

 

Let me know.

Edited April 15, 2015 by Opry99er

[Diecrusher]

Thanks Opry99er!

 

I think that I may have a lead on one offered by another forum member but thank you very much for the offer and I will definitely keep it in mind!

 

Thanks again all for your help..... what a great forum!

[Diecrusher]

Hi all!

 

Well, hopefully I can get moving on this again as I have gotten a MiniMem Module (THANKS Ksarul!!)

 

I am as novice as can be on using the MiniMem however. I am going to try to follow the advise and instructions mentioned above but I am not confident that I will get very far.

 

Could someone give me a step-by-step from the point of inserting the MiniMem and turning the console on?

 

In the meantime I am going to give it a good try and see what I can dig out of the manual.

 

Thanks again!

[Stuart]

(1) Insert MiniMem cartridge and switch on console.

(2) Press any key at the master title screen then select option (2) Easy Bug.

(3) Press any key.

(4) Type C1100<Enter>1<Enter><full stop (.)>

(5) Type M4000<Enter><Enter><Enter><Enter><Enter><Enter><full stop (.)>

 

It should now be showing the contents of memory location >4000 to >4005. These should be >AA, >02, >00, >00, >40, >44. Is that what you see?