(Topic ID: 279195)

MPU LED solid & Testing C23 on Solenoid Driver Board

By EEE

11 months ago


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  • 11 posts
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  • Latest reply 57 days ago by T-Tommy
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#1 11 months ago

I am experiencing a problem with the machine not getting past the initial led flash, it stays on solid.

I read on the pinwiki repair site that when powered on the solenoid driver board C23 capacitor should read very close to 0.30 when the J4 connector is removed from the mpu.

On my stern Nine Ball it shows about 14.68 VDC. I just replaced that cap.

The power supply board readings are about 10% high across the board.

Where should I look next in diagnosing this problem?

#2 11 months ago
Quoted from EEE:

I am experiencing a problem with the machine not getting past the initial led flash, it stays on solid.
I read on the pinwiki repair site that when powered on the solenoid driver board C23 capacitor should read very close to 0.30 when the J4 connector is removed from the mpu.
On my stern Nine Ball it shows about 14.68 VDC. I just replaced that cap.
The power supply board readings are about 10% high across the board.
Where should I look next in diagnosing this problem?

15vdc is a good sign the cap is doing its job. The voltage reads more like 11-12v when this capacitor is failed / out of circuit

I think what you are trying to do is measure the ripple in AC volts. So click your DMM over to AC volts instead of DC volts and repeat the test.

Do note some DMM don't like to measure low AC ripple volts when set to autorange. If the meter read out just constantly bounces around take it out of auto range and go to lowest AC volt range. More than 0.30vac means the cap is not filtering the 12v enough and there is ripple.

#3 11 months ago

Thanks Andrew!

It looks like it’s within spec.

#4 11 months ago

Due to the age of the machine, I just automatically replace that capacitor.

#5 11 months ago

And at the same time, the display HV filter cap too.

#6 11 months ago

I'm still trying to get beyond the mpu led staying solidly lit on power up. All Header pins have been replaced and no apparent acid damage.

The Mpu test points seem to be within reason at approximately 10% variance.
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#7 11 months ago

Looks like corrosion below the 5101 ram chip socket.

#8 11 months ago

MPU is locked up which can be from any large number of causes.

Visual inspection always good starting place. No IC chips with a folded over leg. Blown out parts. Deep gouge breaking a trace. Solder splash....

Check at the CPU chip reset and clock. The clock circuit fails fairly often in the original boards and will lock up the MPU.
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Rotate in known good ICs. Verify the ROMs.

After that stuff it gets more technical, but probably how I would approach it.

So many locked up boards have magically started to work after I replace all IC sockets, rejumper to 2732, and install new roms. Not really something I would recommend tho unless you are well practiced at working on PCBs. 40 years later the IC sockets which may not have been good to begin with are known to be unreliable and a pain to diag. The IC socket may start to conduct from the pressure on the chip leg/dmm lead.

You have some voltage drop on the 12v compared to the driver board (14.5) and MPU (13.4) Should not be bad enough to stop the MPU from booting up but may hint at connector issues.

9 months later
#9 67 days ago

My problem of a solidly lit LED on the mpu has resurfaced.

I have a newer mpu (nvram rev 9), the female connectors on the power supply, solenoid driver board, mpu, etc have been repinned and the test points on the PS, SDB and #3-5 on the mpu all appear to be within the reasonable range.

The original -200 mpu had occasionally demonstrated the same locked on led. I sent it to Nabours for a rebuild and it operated fine for a while before I replaced it with a newer nvram mpu.

I’ve been running led displays for well over a year.

edit..Today I swapped in a different solenoid driver board with no difference.

Any suggestions on what to focus on next?

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#10 61 days ago

User error on this one.

I have an older version of the nvram mpu and it requires that a few jumpers be changed using solder blobs. I missed one.

#11 57 days ago

Nice. Glad you found it. Sometimes the simple things get passed us.

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