Trying to track down this issue on an MPU-200 for Meteor and not sure of the next step:
MPU will boot and I get all 7 'flashes', but it is running slow. It takes about 35 seconds to get thru all 7 flashes, and the 'flashes' themselves last about 1 second each.
I checked the clock into the 6800. Both phases are nice clean square waves, but at about 233kHz each (about 1/4 speed). It is jumpered for the higher clock rate.
I checked resistor values and continuity in the clock circuit, and didn't see any issues.
At this point, I'm looking at U15 or U16 as being the culprit, or maybe the caps at C14 and C15? Is there any way to isolate which component? Those are all part of a feedback loop, so it's hard to isolate without breaking the feedback (i.e. taking something out of the circuit).
TIA

#2 4 years ago

237

slochar

Pinside member

7y 86,550 6,862

Caps first.... there was just a recent thread about these wearing out over time, replace with new. Also, it's the cheapest part of the circuit.

#3 4 years ago

MAX

mbaumle

Pinside member

Gloucester Township, NJ

8y 119K 4,199 18 32

There are jumpers to adjust the clock speed on the M-200 board.

Check for jumpers E32-33 and E34-E35. They should be present for the M-200 MPU. It's possible they've been removed at some point to make the clock speed compatible/slower with the M-100 or Bally games.

Edit: Jumped the gun on my recommendation. Didn't realize you already checked the clock jumpers. Sorry. Good luck tracking down the issue! Wish I could be of more help.

#4 4 years ago

RJB

yendor0

Pinside member

Marion, IA

11y 36,050 131 21

Caps did it, thanks slochar!
Interestingly, C14 and C15 were 470pF. I couldn't see the value when they were in the board, but noticed after I took them out. 470pF is what is used on the Bally -35 boards, but the MPU-200 schematics call for 100pF (and correspondingly have different values for R4 and R10). Am I correct that the RC combination sets the clock rate, so 470pF would be wrong for MPU-200?
Also, the only 100pF I had were ceramic disc. Do those need to be mylar/mica/tantalum for better tolerances?

#5 4 years ago

PIP

Quench

Pinside member

8y 114K 8,020

OP
Quoted from yendor0:
Am I correct that the RC combination sets the clock rate, so 470pF would be wrong for MPU-200?
Also, the only 100pF I had were ceramic disc. Do those need to be mylar/mica/tantalum for better tolerances?

The originals are 100pf ceramic disc capacitors.

Yes, the RC combination sets the pulse length and the two identical multivibrators feed back on another to produce your 50% duty cycle clock.

Note the timing resistors R4 and R10 are oddball values at 13.7k ohms - you won't find them at your corner electronics hobby store so will have to get them from the big guys, eg:
https://www.mouser.com/ProductDetail/594-5053HD13K70F

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