Atari TT - Bus errors, advice needed! - SOLVED

[Atarian Computing]

Quick update:

* noticed that if I remove the ST ram card the machine will boot from floppy and read the floppy fine
- But when loading mint it still gives a memory address / bus error in the system log
* Running yaart crashed with the ST ram card installed, but not with it removed

I know you could assume that it's related to the ST ram card but I don't think so as Mint will still show a bus error upon loading, but with it removed does solve the floppy issues. I am feeling that it's something to do with memory address allocation, where adding the extra memory space causes issues or makes the issues worse somehow, but I still feel the issues are underlying even without the card installed.

Could some of the TT experts let me know what they think of this? Is there a certain chip in charge of memory allocation. Could adding the ST ram card cause something to do with how the floppy uses memory space/locations?

I know from experience and from others (Tuxie) that TT-Ram and ST-Ram sockets go bad. It's not at all unusual to replace them. Symptoms with bad TT-Ram sockets are as you experienced but yaartt would show problems as well. Whatever it is, it's likely a small thing that's hard to track down.

[exxos]

Maybe its a bus loading issue.. I get it all the time, its why I swap out the SIP's for 2.2K ones now.. at least in the STFM & STE.

[Steve]

Maybe its a bus loading issue.. I get it all the time, its why I swap out the SIP's for 2.2K ones now.. at least in the STFM & STE.

I am new to SIP resistors :)

I have the following types on my board:
M9-1-102J 124
M9-1-122J 104
103J 120
R 220J
4 102J

Would you suggest replacing *all* of these with 2.2k ohm versions? and perhaps socket them? Thanks

ALSO I found one cracked resistor, colour codes: brown green brown silver silver, found near the rear I/O ports. I'll replace that. I think that equates to 1.51 Ohm +/- 10%.

[exxos]

Looking at the schematic, they are all 10K on address and databus..

I would just solder some 4.7K arrays on the bottom of them on the PCB, see if it works before changing them as of course runs the risk of damaging tracks..

Of course its only a guess to your problem, I see problems with bus loading on STE, STFM all the time so possible could be a problem on TT..

[Steve]

Looking at the schematic, they are all 10K on address and databus..

I would just solder some 4.7K arrays on the bottom of them on the PCB, see if it works before changing them as of course runs the risk of damaging tracks..

Of course its only a guess to your problem, I see problems with bus loading on STE, STFM all the time so possible could be a problem on TT..

Thank you Chris, this is fine I know it is a guess. You see, I am happy to try *anything* to fix my machine.

Please could you let me know how many I need, and which ones in the list I posted above are 10k? I don't know how to read these figures.

[Atarian Computing]

Looking at the schematic, they are all 10K on address and databus..

I would just solder some 4.7K arrays on the bottom of them on the PCB, see if it works before changing them as of course runs the risk of damaging tracks..

Of course its only a guess to your problem, I see problems with bus loading on STE, STFM all the time so possible could be a problem on TT..

Thank you Chris, this is fine I know it is a guess. You see, I am happy to try *anything* to fix my machine.

Please could you let me know how many I need, and which ones in the list I posted above are 10k? I don't know how to read these figures.

Sketch (39).png

Looking at the highlighted components, RP*** (RP stand for Resistor Pack), they are clearly (as they usually are) bussed. Meaning all resistors share common VCC (Pin 1 +5V in this case). There are 8 other pins, so 8 resistors + 1 VCC. That isolated SIP on the left I don't know if matters, it's not on the data or address bus. So you might wanna leave that alone.

So you will look for Resistor Pack/Network/Array - Bussed (not isolated) - SIP/SIL - Through Hole and you end up with this:
https://www.digikey.fi/products/en/resi ... ageSize=25

I use these all the time: https://www.digikey.fi/product-detail/e ... ND/3593671

[exxos]

:goodpost:

No harm in tagging one on that also I guess..

Probably 4.7K ones would be a good one to try I think thinking about it a bit...

[Steve]

Ok guys, I've ordered the parts - hopefully they will arrive tomorrow. PS THANK YOU for supporting me through this repair, it is most appreciated. Like I say, my soldering skills are top notch, but my schematical/technical knowledge is limited.

Atarian - could you do me a massive favor and just help me pin point the SIPS on the motherboard photo? There are 7 surrounding the TT ram VME header, one underneath the DMA's, two under the ST ram, two above the VME riser and one near the floppy controller. Are these the ones I'm interested in?
- Also just wondering - The MC146818AP (next to the floppy controller) and the square atari custom chip 9127FLA (under the yamaha chip) are absolutely stone cold when the machine is running, is this normal/suspect? Is there a way I can test if these chips are working with a multimeter? Thx

Exxos - So I'm just soldering these onto the bottom side of the mobo, under the existing SIPS, is there a polarity I need to worry about?

Thx again

[Atarian Computing]

Here are the SIPs on your board:

Inked20170304_112017_LI.jpg

[exxos]

Exxos - So I'm just soldering these onto the bottom side of the mobo, under the existing SIPS, is there a polarity I need to worry about?

There is a "dot" on the SIP which shows pin 1.