Determining Health of A4000 Mainboard

[irishmike]

Hello All:

I borrowed a known good A3640 processor card from one of my local Amiga User Group members in order to test my A4000 Mainboards.

We have previously determined that the PSU is good by checking voltages under load.  

I seated the A3640 card to one of the two mainboards and put a stick of RAM in the first slot (towards the Processor board) hooked up my 1084S to the video port and turned on the PSU.  Got a series of green and yellow screens which flickered for 2 minutes but nothing more.  

The other mainboard is apparently DOA completely because you get no video. EDIT:  This board is missing a chip that the other one has in socket U103 (this is on a REV B board).

I waited 3 full minutes to see if it would go the KICK ROM (there is no floppy or hard drive connected currently).  Is the mainboard good or am I missing something?  EDIT:  This is the board that gave the colors on the screen, not the one that had no video ;-)

Help would be appreciated.


Thanks,

Mike

[irishmike]

Hello All again:

In doing a Google Search, the green screen may be bad chip ram and the yellow may indicate that the CPU found an error... is there anyway to get more information?  Is this accurate for the A4000?

Thanks,

Mike

BTW:  The only RAM on the board I am aware of is in the SIMM area of the board.  The SIMMs I have, may indeed be bad.

Thanks again.

[patrik]

1. Do you have the stock doublesided 2MB SIMM to try with as chipmem, just to be sure there arent any compatibility issues?
2. Are the motherboard INT/EXT jumpers set to EXT for use with the A3640?

The colours, especially if they arent consistent will not tell you more than that "something" is wrong.

Also even if you get one consistent colour, it is not a very precise indication of what is at fault - say if you get a green screen for chipmem error, it might not be the chipmem itself which is at fault, but something else needed to make it function. Say in the case of the A500/A2000/A3000 a green screen more often means that there is oxidation and bad contact in the Agnus socket. This should not be the case of the A4000 as Alice, the Agnus equivalent in the AGA chipset is soldered to the motherboard, but I was just making an example.


/Patrik

[irishmike]

@patrik

The jumpers you mention, do you have numbers where these would be located?  Are they on the Processor board or the Mainboard?

The RAM is not the stock ram.  What would be the RAM I need?  I have two single sided 72 PIN SIMMS.  All I can tell you for sure (because my reading the numbers on them skill is VERY rusty) is that they are 80 ns.

Does the ram need to be parity or non-parity?

Thanks for your help!

Mike

[patrik]

@irishmike:

The INT/EXT jumpers are a pair of jumpers (two) located on the motherboard, under the processor card, so you need to remove it to get access to them. They are marked as INT/EXT on the motherboard in white, printed letter.

The chipmem simm need to be doublesided to give you a full 2MB of chipmem. If not - say if you use a singlesided 4MB simm, you should get 1MB chipmem, but the computer should still work. Usually a doublesided 8MB simm works. Parity is ignored.


/Patrik

[tonyvdb]

Mike,
What is the condition of the Battery and the area around it?
Battery leakage can cause the traces to become dammaged and because the 4000 mb has layered traces it can sometimes be tough to see.

[irishmike]

@tonyvdb

Both the mainboards have had the battery removed and there is no sign that they were ever leaked upon.  The one I am working with that seems to be fine (and actually I determined that it is in fact working just now) has the button cell modification made to it.

@patrik

Thanks a bunch!   It turned out that the INT/EXT jumpers were fine, but there was no jumper on the SIMM SIZE jumper.  Also the CHIPRAM jumper was set to the wrong size.  These corrected and the insert floppy kick screen came up!  I believe the board is in good shape!

Now I just have to find the rest of the parts to build the A4000 :-)

Again, Appreciate your help on this :-)

[doctorq]

Now I just have to find the rest of the parts to build the A4000 :-)

Have you recently looked in the thread where you requested you parts?

[irishmike]

@doctorq

Hello:  Indeed I have and thanks.  I did decide however that I want to go with the A3640 because according to my case, this was what this machine was from C= :-)   If you have the daughterboard and the case parts however, I may be interested in obtaining those!   I am waiting to hear from a fellow that is here in the States on both the Processor and Daughterboard, if we can come to an agreement on price -- then that will likely be the way I go.  The case is another story altogehter.

In any case, I will PM you when I find out :-)

Thanks my friend!

[irishmike]

Was just thinking (I know how dangerous this can be) -- I think my second A4000 Mainboard is probably good too... it is missing some jumpers and the chip marked U103... can someone tell me what this chip is?  That may be it.

Thanks for the help so far :-)

[ZXoney]

U103 is a 74FCT244T this chip is need for the CPU CLK Source, I don't think the A4000 would function without it!

-=(ZXoney)=-

BTW,

74244 is a TTL check this link for specs.
http://www.idt.com/?genID=74FCT244T

[irishmike]

That is probably the problem with the second board then :-)  Aside from three missing jumpers :-)

Cool.

Thanks,

Mike

EDIT:  Could use one if someone has one.  PMAIL me :-)

[irishmike]

Hello Again All:

I am trying to track down this IC for U103 (74FCT244T) as suggested by ZXoney.

We can't find a good crossreference on any of the semiconductor suppliers I know.  There was one that had a 74HCT244T (must buy quanity 10), I wondered if that would work or if someone knew of a good replacement part.

Obviously, if someone has an A4000 mainboard with battery acid damage or otherwise unrepairable situation with a good chip on it, I would be interested.   They cost $.60 USD each or $.33 each from the supplier I mention, so basically my offer is whatever it takes to ship them safely.

If you can help there, please PMAIL me!

Otherwise, good replacement advice is welcome.

Thanks,

Mike

[dnelsonfl]

I looked on a few suppliers, too, for the 74FCT244T, and the ones I came across that were available were not the DIP package but the kind meant for soldering (with the bent legs). Hope I described that right. So it begs asking if that kind can be adapted to fit. Smallest was quantities of 10, again. Maybe we looked at the same places.

[irishmike]

@dnelsonfl

hmmm, this was a DIP package but the "H" in place of the "F" bothers me a little... I guess that I don't mind quanity 10 for $4 USD.  As long as the IC is one that works identically.

But these were definitely DIP packages.