Color Ram Bank Error - Write 5555 Read B240

[Zellez]

Hi guys,
I've got a M1BBV board that has the error:
Color Ram Bank Error - Address 0040000 Write 5555 Read B240.

It was working fine until approximately a year ago, then I stored it away and now that I've tried to plug it, got the above issue.

What can I do to fix it? Searched a bit on the internet, and found that it could be some bad chip, but I?m not really sure how to identify the broken one and where to start.

Can someone point my in the right direction? Thanks!

 

[aha2940]

it may be a broken chip, because the difference in values is big (more than one bit):

5555 = 0101 0101 0101 0101
B240 = 1011 0010 0100 0000

As you can see, there are 9 different bits between the two values. That, to me, seems hard to be caused by a single trace being broken.

Regards.

 

[GadgetUK]

Edit: scrap what I said - looks like a RAM error or something to do with WE pin.

 

[bustedstr8]

Edit: scrap what I said - looks like a RAM error or something to do with WE pin.

Yup...looks like a /WE issue. The BRAM will also spit out a B240 when the /WE is bad.


The Color RAM /WE is the OR of the NEO-C1 PAL and WE signals (pins 16 and 32). So if you start there you can hopefully trace the problem.

 

[Xian Xi]

B240 is a RAM /WE error caused by an open transistor on the /WE line, usually located on the back of the board. Most times labeled as Q1.

 

[bustedstr8]

B240 is a RAM /WE error caused by an open transistor on the /WE line, usually located on the back of the board. Most times labeled as Q1.

Ya...the transistor is usually the problem for the BRAM /WE.

This is the first time I have noticed the Color RAM spitting out B240. The Color Ram only has one control signal, all the others are tied to +5 or Gnd ( /CS1 CS2 and /OE)

 

[Zellez]

Thanks a lot for all the answers.
I've tried to find the Q1 transistor on the back, but saw only Q2 and Q3.
Noticed that the soldering is not that good there, so I wonder if that could be the problem and how that happened since last year the board was working.

 

[Xian Xi]

Check if either of them connect to the /CE or /WE line on the RAM.

 

[GadgetUK]

If its anything like the MV1-FZ the Q1 is not marked and sits under the area near the backup RAM. I didn't realise Q1 was related to Color RAM?!?

 

[Zellez]

Both Q2 and Q3 connect to the Neo C1 pins 16 and 32, so it might be something else.
Still wasn't able to find Q1 though

 

[bustedstr8]

The transistor outputs should trace to an OR gate (either a LS/HC32 or the NEO-GO pins39,40 depending on hardware revision)

The OR output (from a LS/HC32 or NEO-GO pin41) is your /WE. It's pin27 for the 6264 Color Rams. If everything traces out with continuity you have a bad component somewhere that needs to be replaced.