Re: Stern MPU-200 REV-A LED problem
- From: "seymour-shabow@xxxxxxxxxx" <seymour-shabow@xxxxxxxxxx>
- Date: Fri, 22 Feb 2008 08:50:19 -0500
Pinballed wrote:
The LED stays on. Here's whats known to be good...Game (Meteor) works
with another CPU...all functions normally. THIS CPU stays lit. All the
chips are good...tested them ALL, new roms etc. Here's where it goes
wrong. Pin 5 at U9 is simmerring at 3.9 VDC. So it's not pulsing
properly and the CPU will never turn on. Getting proper pulses and
power at other key pins at U9. So I started checking things out
between boards and I noticed something that I'm not sure is correct.
The resistors at R4 and R10 are 13.7K and are huge. The schematics I
have call for 5.6K. (The other board I have has 5.6K resistors there.)
I think thats draining R6 which normally should be 1K but this one is
reading 3.3k. And the C14 and C15 caps arent functioning properly.
(same value on both sides when board is powered) They are directly
linked to what appears to be those wrong resistors. But I cant be sure
if those in fact, ARE the wrong resistors because I dont have a
schematic for this board. I'm using the Bally schematic and just
visually comparing with a Stern MPU 200...but not the REV-A version
that I'm working on.
Regardless...did someone just put the wrong resistors in there and
replacing them with the proper ones...as well as the C14,15 and R6
should remedy this? Or...do those happen to be the proper resistors
for that board? I sure hope they aren't. Because that should do it.
Signs are pointing towards U16 being bad - a 9602 which is hard to find. See http://www.flipper-pinball-fan.be/ for info on replacing it if you can't get one. If it's socketed on your boards you could swap from the working one to the other. The schematics I have for the mpu200 show 13.7k 1% as being the resistors 4, 10 too.
Do you have an oscilloscope or logic probe you can test the clock and rule that out at the 6800 pins 3 & 37..... also do you have the board jumpered correctly for the Roms you're using? Have you tried the leon test chip yet.... that will help you narrow down what's causing the problem.
Be aware also that the mpu200's 5101s must be a faster variant that the bally -35 board uses - -45 (450ns) work in a bally board but usually not in the stern boards you need -3 or -15 (300ns or faster) for the mpu200 boards. With the test chip you can try it without the ram to see if this might be the problem.
The seawitch 11x17 schematic set on IPDB is very readable - also on Monday I have at work a redrawn mpu200 I could send you if you need it, it's not checked against a board but I suppose that's the next step in cleaning it up..... also making a key for the parts as it took me a bit of scrolling around to find the 2 resistors you reference!!
-scott CARGPB#29
.
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