504B MPU Problem

[cowboygames]

A while back I'd posted about an issue where I turned my machine on to a RAM error and ended up swapping the ram chips on the board to solve the problem...I thought. A few weeks ago the same board started acting up again except that it would go into a ram error while the machine was on and running. I'd do the normal resets and only lose whatever credits were on the machine at the time of the error, all game settings stayed intact so it was just the MPU ram that was being affected. A couple weeks ago it went into error and wouldn't reset, had the red light on the MPU and couldn't get it to work so I swapped the board out and the machine has been working fine since. Anyone ever experienced this before or have any ideas what might be going on? CMOS battery is showing 2.899 volts, which is low, but not critically low by any stretch of the imagination. And why would it do this only after the machine had been running for a while? Pretty mysterious I wouldn't worry about it, but I paid $80 for this board about a year ago. Definately one of the most expensive boards I've ever bought and my only 504B. Thanks in advance for any help or suggestions

[stayouttadabunker]

There IS a threshold point of charge at which a low battery will make the MPU show that error.
I don't know what the voltage number would be for that particular point the battery capacity charge is though.
It may or may not be in the board specs somewhere.
for example: I know I've seen it written once somewhere in an S+ manual.
Problem is: There's so many bloody pages of S2000 manual materials I don't know where the reference to the threshold is. 

Anyways, by the time you get a battery meter on it - it's almost too late
and the battery surges back to a point to where it appears okay.
I would still suspect the battery because that's the only thing that can keep the memory intact.
Unless...there's some other nearby IC component that could be going out of specs -
causing the flaky memory.

[cowboygames]

I was thinking along those lines, but while the machine is running I wouldn't think the error would pop. I would think it more likely to be a startup problem.
I beleive the threshold on these is around 2.4v or something like that and this battery was new when I got the board about a year ago. Maybe I have some type of short that's draining my battery or interrupting the power to the ram chips???

Yeah, I know, I know, new don't mean crap except that it SHOULD last a while :97

[stayouttadabunker]

I agree..."new" or "newer" doesn't always mean better...
You just got unlucky with a lemon board maybe?
I have an old 502 that's NEVER given me any problems for 3 yrs so far...( knock on my wooden head )
You won't BELIEVE how many games I've changed on that MPU...

[cowboygames]

I don't like lemons ...

[Foster]

Do yo have the rechargeable battery pack on the board?

If not did you solder a jumper between the two solder pads for the positive pole of the battery.

If not try soldering one in. if it helps. if it does not solve the problem, leave it installed anyways, it wont damage anything.

I had a 502A/B that I removed that battery and it started to reel tilt either reel 2 or 3 95% of the spins it tried to complete
the spins would be from game play or a reset spin from a prior reel tilt.
I even rebooted the machine, no help
Once I put that jumper on the positive solder pads, the reel tilts went away.
I did test them to see if the board had them connected via a hidden trace without the battery there. not connected.



 

[cowboygames]

I'll give that a try as the battery is gone, but on the other hand, the board worked fine for a year before it started acting up. Thanks for the suggestion Foster, I'd forgot about that one

[Foster]

Another suggestion is to borrow a set of the RAM chips from a known good board
they are the 2 unlabeled chips between the game chip sockets and VS and SS chip sockets.

One of them could be about to fail.

[cowboygames]

That's what I did the first time the board acted up. Unless something about the board is wrecking ram chips I've already tried that

[Mirage_Chaser]

In my experience even a battery that is over the "will cause problems" threshold can be an issue. If your board is having ram problems I usually go to the battery first.