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Neo 4 Slot BRAM error---SOLVED (Post 20)

Mitsurugi-w

Mitsurugi-w

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Can anyone help me make sense of this one?

I have checked around the battery and there is no corrosion and I didn't see any broken traces when I examined it. What else should I check?

35j0brr.jpg
 
Check for bad traces to the backup ram chips. If all is good you could try swapping them from a parts board.
 
Come on guys, lets help Mitsu out with this.

Anyone seen/troubleshoot this error before? Or know someone that has work on these boards?!
 
Derick2k said:
Or know someone that has work on these boards?!
Click to expand...
Channelmanic does on KLOV. But he's months and months out for repair work last I read. He's a wealth of knowledge though, narrowed down some other RAM errors on my 4-slot through the forum and I got it up and running again.
 
Derick2k said:
Come on guys, lets help Mitsu out with this.

Anyone seen/troubleshoot this error before? Or know someone that has work on these boards?!
Click to expand...
Yes I've fixed a similar backup RAM error. I told Mitsu to check the data lines from the lower backup ram to D0-D7 of the CPU.

Here's the pinout, quoted from MKL:

MKL' said:
RAM___CPU

1______43
2______41
3______36
4______35
5______34
6______33
7______32
8______31
9______30
10_____29
21_____39
23_____40
24_____38
25_____37
26_____42

etc.

There are 3 pins for each backup ram chip that are not connected to the CPU:

lower ram:

20_____74HC32 (13) located at D10
22_____PRO-C0 (16)
27_____74HC32 (8) located at D10

higher ram:

20_____74HC32 (13) located at D10
22_____PRO-C0 (8)
27_____74HC32 (6) located at D10
Click to expand...
 
Ok. I checked and all of the pins show continuity . Checked the upper ram also just for the hell of it. What's next?
 
Put the code into a hex to binary converter. That's how you see where the problem is.

5555 is the A-OK code which is 0101 0101 0101 0101, the digit all the way on the right is the 1st bit of data, there are 16 data lines aka 16 bit.

So if you get a 5545 it would be 0101 0101 0100 0101, so the 5th bit isn't reading right. That means the 5th data line on the lower BRAM is the problem.

This is what I remember from Nightmare Tony teaching me.
 
So is it looking like bad ram itself if all of the traces show continuity?
 
Make sure the BRAM is connected to WRAM, CPU and Bios.
 
The data pins. If it's the 5th bit then it would be the D4 line.
 
I'm not a board repair tech so not sure what that means as far as tracing it back.

Thanks for your patience.
 
This should help.
 

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So would lower backup ram be considered ram3?
 
Shit, forgot this was for a 4 slot, that pinout is for an MV1C, different bios pinout.

Lower RAM is the ram with the data lines that are the lower half connected to the 68k.

For example, 16 data lines D0-D15, D0-D7 are the lower half so which ever ram's data lines are connected to those pins on the 68K is the lower work RAM. Work ram and backup ram work in pairs. Each WRAM will have a BRAM connected to it. You can easily find which one with the multimeter.

Download the datasheets for each item, that way you can see the pinouts and follow them with ease. Doing it this way is the best way to learn how to do some board repair yourself.

Let me know if I missed anything.
 
@Mitsu:

During the memory test four patterns are written to the RAM and then verified:

0x00 (00000000)
0x55 (01010101)
0xAA (10101010)
0xFF (11111111)

The 68000 is a 16bit CPU so it does that twice, on odd and even or low/high bytes. Your unit has a bit failure on the low byte for the address listed on the screen. It wrote 5555 and read back 5545. Means that the data line D4 returned "0" instead of the expected "1" for that particular address.
 
I love you guys, awesome info.

Just wish I could understand it,
This how I feel right now :D
200w.gif
 
l_oliveira said:
@Mitsu:

During the memory test four patterns are written to the RAM and then verified:

0x00 (00000000)
0x55 (01010101)
0xAA (10101010)
0xFF (11111111)

The 68000 is a 16bit CPU so it does that twice, on odd and even or low/high bytes. Your unit has a bit failure on the low byte for the address listed on the screen. It wrote 5555 and read back 5545. Means that the data line D4 returned "0" instead of the expected "1" for that particular address.
Click to expand...
Yeah it's an error in lower backup ram. So far I traced all pins on the ram to the cpu and to the 74HP32P as well as from the 10k resistor after the battery circuit. I have continuity everywhere. Not sure what else to do other than swapping ram. The ram is ordered just in case but might take a few weeks.
 
swapping the ram will tell you if the problem comes fom the ram chip or from somewhere else. my guts tell me is not the ram chip but its worth a shot.
 
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