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MPU4 Lamp Matrix Fault Help


netdent
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Thought I would start a thread! This board works perfect apart from stuck lamps? The whole reel glass area come on solid from power on and stay on but seem to flicker sort of in attract! however there is little or no lamps in the top glass.

I metered all the triacs and was sure T45 was reading short to it's tab from one side but upon removal it reads fine as does the board with it removed? unless the heat desoldering it un shorted it again? Not replaced it as yet just wondering what else to check while board is out?

 

Thanks Ronnie

 

 

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9 minutes ago, fruit58 said:

most of the mod 2 are like that ic 13 is that a small crack  on it all so some times them transistors can go leaky rather than going short hope this helps

Thanks yes all info helps, can't see a crack on ic 13, but would a leaky triac light all the bottom glass lamps and cause none to light on top glass?

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Just now, netdent said:

Thanks yes all info helps, can't see a crack on ic 13, but would a leaky triac light all the bottom glass lamps and cause none to light on top glass?

They are not triacs, they are darlington transistors for the lamps. Triacs are AC switching devices for the solenoids, lockouts etc

One dodgy transistor won't cause the symptoms you are experiencing. I guess you need to work out whether it's a row fault or column fault

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1 minute ago, Wizard said:

They are not triacs, they are darlington transistors for the lamps. Triacs are AC switching devices for the solenoids, lockouts etc

One dodgy transistor won't cause the symptoms you are experiencing. I guess you need to work out whether it's a row fault or column fault

Cheers Wizard, so would I try leaving either the row or the column plug on the mpu to see which puts out the stuck lamps? is it looking more like a PIA fault if unlikely a transistor?

Cheers Ronnie

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18 minutes ago, netdent said:

Cheers Wizard, so would I try leaving either the row or the column plug on the mpu to see which puts out the stuck lamps? is it looking more like a PIA fault if unlikely a transistor?

Cheers Ronnie

No, pulling out either will turn off all the lamps

I suspect one of the ULN2803s might be bad ( or IC3 that drives them ) , check the output pins 11, 12, 13, 14, 15, 16, 17 & 18 and see if they are stuck lo

Also check that you are getting high going pulses on the yellow connector pins 1, 2, 3, 4, 6, 7, 8 & 9 ( only one should be high at any one time )

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13 minutes ago, Wizard said:

Maybe, depends on whether the game starts up without any switches connected, it needs to be running

Cheers I have a whole box of mpu carts hopefully one will run on the bench

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39 minutes ago, netdent said:

Right I'm not sure if the game is running or not! But all those pins ic13 and 14 are high and the yellow plug pins are pulsing ? I have a spare alpha but it's wired for mpu3

 

Thanks Ronnie

So if all those outputs are high, there should be no lamps on at all, so I suspect a bad T22-29 or T30-37. Measure all the voltages on the green socket without the loom connected and see if any are ~34v, if so that is a bad transistor

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Right! I decided to ft the board to the machine as I could not see what was going on, bottom lamps still solid, restricted light and space I must have shorted pins 10 and 11 of the uln! it went up like a firecracker! Busy replacing that just now, hope nowt else blew!

 

Cheers Ronnie

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Right probed all those pins again so

IC 14 pins 11 to 14 are oulsing but some go high when probe is held on pins 15 to 18 are high when probe attached some lamps come on in bottom glass

IC 13 pins 11 to 18 are all high and each when probed will light some top lamps

the segment plug pins 1 2 3 4 5 7 8 and 9 are all pulsing?

Thanks Ronnie

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