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


Diecrusher

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This is what I found.

 

(1) Typed C1100

(2) Typed "1" (FDC Indicator lights and stays lit solid)

(3) Mem locations show 4000=AA, 4001=02, 4002=AA, 4003=02, 4004=40, 4005=44

Compare some more bytes - they should be as below. But it looks as if what you're seeing is each pair of bytes being repeated? Which I think points to a stuck address bit A14? Do you get the same (repeated bytes) with the 80 track EPROMs?

 

DATA >AA02 standard header mark, version 2

DATA >0000 no programs

DATA >4044 power-up chain ptr

DATA >0000 programs chain ptr (none)

DATA >404A DSR chain ptr

DATA >4010 subprograms chain ptr

DATA >0000 ISR chain ptr (none)

DATA >0000

DATA >4016 link to next subprogram

DATA >5B38 address of that one

 

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Compare some more bytes - they should be as below. But it looks as if what you're seeing is each pair of bytes being repeated? Which I think points to a stuck address bit A14? Do you get the same (repeated bytes) with the 80 track EPROMs?

 

DATA >AA02 standard header mark, version 2

DATA >0000 no programs

DATA >4044 power-up chain ptr

DATA >0000 programs chain ptr (none)

DATA >404A DSR chain ptr

DATA >4010 subprograms chain ptr

DATA >0000 ISR chain ptr (none)

DATA >0000

DATA >4016 link to next subprogram

DATA >5B38 address of that one

 

Sorry Stuart, I don't quite follow what you mean by this I am such a noob. How would I go about doing this??

 

I did put the old 40-track ROMs back in and got the same exact values as I did for my new 80-track ROMs.

 

Another thing that I noticed is that the 74LS74AN chip @ U11 and the 74LS32N chip @ U21 located near the 5v regulator are quite a bit warm than the others on the board, approx. 60c. I don't know if this is normal or not but figured that it was worth mentioning. Those are the only 2 chips around that area that I haven't socketed and replaced.

 

Checked the 5v numerous places on the board and it seems fine but haven't checked to thoroughly.

 

Thanks.....

Edited by Diecrusher
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Compare some more bytes - they should be as below. But it looks as if what you're seeing is each pair of bytes being repeated? Which I think points to a stuck address bit A14? Do you get the same (repeated bytes) with the 80 track EPROMs?

 

DATA >AA02 standard header mark, version 2

DATA >0000 no programs

DATA >4044 power-up chain ptr

DATA >0000 programs chain ptr (none)

DATA >404A DSR chain ptr

DATA >4010 subprograms chain ptr

DATA >0000 ISR chain ptr (none)

DATA >0000

DATA >4016 link to next subprogram

DATA >5B38 address of that one

 

Sorry Stuart, I don't quite follow what you mean by this I am such a noob. How would I go about doing this??

 

I did put the old 40-track ROMs back in and got the same exact values as I did for my new 80-track ROMs.

 

Another thing that I noticed is that the 74LS74AN chip @ U11 and the 74LS32N chip @ U21 located near the 5v regulator are quite a bit warm than the others on the board, approx. 60c. I don't know if this is normal or not but figured that it was worth mentioning. Those are the only 2 chips around that area that I haven't socketed and replaced.

 

Checked the 5v numerous places on the board and it seems fine but haven't checked to thoroughly.

 

Thanks.....

 

What I meant - and I wasn't particularly clear ;-) - repeat what you done with the MiniMem cartridge, but after the "M4000", keep on pressing <Enter> to display lots more bytes from memory, rather than just 6 bytes from the earlier test. Do 20 bytes and report back what you see.

 

The two chips that are warm - is the voltage regulator hot as well? Could they just be getting radiated heat from the regulator?

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Thanks Stuart for clarifying that.

 

 

Here are some more values that I found:

 

M4000 > AA

M4001 > 02

M4002 > AA

M4003 > 02

M4004 > 40

M4005 > 44

M4006 > 40

M4007 > 44

M4008 > 40

M4009 > 4A

M400A > 40

M400B > 4A

M400C > 00

M400D > 00

M400E > 00

M400F > 00

M4010 > 40

M4011 > 16

M4012 > 40

M4013 > 16

M4014 > 01

M4015 > 10

M4016 > 01

M4017 > 10

M4018 > 5B

M4019 > 48

M401A > 5B

M401B > 48

M401C > 40

 

It is strange but the regulator itself reads a lower temp than the 2 chips mentioned above. I was using a Infared Temperature Gun however and I am not sure how accurate that is.

 

Thanks.

Edited by Diecrusher
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I'd say that indicates a problem with address bit A14. This is buffered onto the board by U2 (74LS244) and feeds the two EPROMs, the FDC chip, U23 (74LS259) and U22 (74LS251). The EPROMs are probably OK as swapping between the 40 track and 80 track versions makes no difference. The FDC chip you've tried in a different system and that is OK. I'd try removing U2 and fitting a socket, but before you pop in a new chip, measure the resistance between the EPROMs pin 7 and GND - is it a dead short? If yes, has the board ever worked since fitting the sockets for the EPROMs? If no or unsure, it's possible that fitting the sockets has shorted that pin. It's possible but less likely that U21 or U22 are shorting that address line - could try replacing those as well.

 

Wouldn't worry about the warm chips at the moment. Sort out the memory problem first. They might just run warm normally anyway.

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SUCCESS!!!!!!

 

But it was not what I expected.....

 

I socketed and replaced quite a few chips on the board the last few being U2, U23 and U22. No difference. I checked for shorts and found none.

 

I tried swapping out the 40-track ROMs for the 80-track ones, no difference. I did notice that the machine would boot with no ROMs installed at all so that got me checking the sockets that

I put in for the ROMs. I checked all of the socket pins with their corresponding traces for continuity and everything checked out. No shorts either that I could find. The soldering job looked clean.

 

I had originally installed the high-qualitiy machined gold-plated pinned sockets but figured that I might as well try to replace them with regular 24-pin sockets I bought too.

 

To my suprise everything now WORKS so I am guessing that was the problem all along! Sheesh! No regrets though as I learned alot and quite a few of the chips have brand new replacements and will

be easier to replace if necessary in the future.

 

THANKS AGAIN EVERYONE! 1 down, 1 to go..... now on to the 32k card.

 

I ran the p/card program on the TI Diagnostic Disk with a known working 32k card and it finishes the test. With the faulty 32k card the test immediately reports an error and ends. Here we go again! :)

Edited by Diecrusher
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I definitely need to scan the copy of the 32K troubleshooting guide I have. . .it may come in useful here. I would probably look at the buffer chips first though--assuming the card is even getting power.

 

It is unfortunate that I'm out of the PEB Extender boards right now--you could probably use one to good effect here.

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... I had originally installed the high-quality machined gold-plated pinned sockets but figured that I might as well try to replace them with regular 24-pin sockets I bought too.

 

To my surprise everything now WORKS so I am guessing that was the problem all along! Sheesh! ...

 

What?—so better is worse? Did you replace/check the machined sockets one at a time or replace them all at once?

 

...lee

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One thing I have noticed with Machine Pin Sockets is that the source is VERY important. I have received sockets that were missing the inserts on one or two pins or had inserts that were loose in the pin so that they made very poor contact. Even from the sources with bad sockets, only about 3 in 100 are bad--but if you don't look at them carefully, those bad ones can bite you. The good ones from the same lot work great--the problem is in the quality control at the factory.

 

Augat is generally perfect quality, as are several other sources. The ones from Taiwan are also almost uniformly good. It is the ones with dubious origins that you have to watch out with--and it is hard to know if they are bad until you've inspected them. Often these will be surplus, no-name brand lots that ended up surplussed because they were questionable when initially inspected by the receiving factory. It was cheaper to write them off and buy new ones than it was to sort out the bad ones. . .

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I have no idea what happened. I just replaced the ROM sockets only and follow ed the same methods. I am very careful with my soldering job. The machined sockets themselves looked good too, purchased locally. Maybe the round pin sockets didn't make good enough contact with the flat pins on the chip and that is why the replacement non-machined sockets worked better? I have no idea except that now it works fine.

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I have no idea what happened. I just replaced the ROM sockets only and follow ed the same methods. I am very careful with my soldering job. The machined sockets themselves looked good too, purchased locally. Maybe the round pin sockets didn't make good enough contact with the flat pins on the chip and that is why the replacement non-machined sockets worked better? I have no idea except that now it works fine.

 

Back when I was doing the 80 track upgrades for the TI Disk Controller, I used the machined sockets. If you look at the board, there are traces that run between the pins.

If you push the socket all the way in, it will short some of the socket pins to those traces. You'll never find that with an ohmmeter if you just check the socket pins. The tip I gave to everyone doing the upgrade was to leave the socket up off the board a little, don't push it all the way down. That way you'll avoid shorting the socket pins to the in-between traces.

 

Gazoo

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One thing I have noticed with Machine Pin Sockets is that the source is VERY important. I have received sockets that were missing the inserts on one or two pins or had inserts that were loose in the pin so that they made very poor contact. Even from the sources with bad sockets, only about 3 in 100 are bad--but if you don't look at them carefully, those bad ones can bite you. The good ones from the same lot work great--the problem is in the quality control at the factory.

 

This is one of the reasons I still use double-wipe sockets for most of my repair work.

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I tried to look 'through' the PCB with a bright light from the opposite sides with a pair of magnifiers and could swear that none of the pins were double-touching but I must have missed one. Sure makes sense that it was probably the fault. Great future advice Gazoo for what to look for! Thanks.

 

So guys, any ideas for troubleshooting the 32k card. I will dig further online. I've got a scope and logic probe that sadly I have never used and now might be the time!

Edited by Diecrusher
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