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MPU4 board repair advice


Prototype_uk
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3 hours ago, midibob said:

The PIO's you can get from Ebay but it's a case of Caveat Emptor as there's so many Chinese knock off's about! A spare board (if it's cheap) is your best bet although look for a MOD2  as on MOD4's all the leads are cropped and no good for fitting in a socket.

Good advice thank you. Do these look genuine to you? 

https://www.ebay.co.uk/itm/274346525722?hash=item3fe053c41a:g:9q0AAOSwZDleov8~

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Thinking outside the box it's obvious but are those resistors the right value? I've only done one mpu4 repair so I don't know them to well. Watching the thermal video they're getting very fecking hot... Where is the power going and is it related to the other IC getting hot? I couldn't really tell what's happening in the vid... just asking out of interest. 

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11 hours ago, MattyL said:

Thinking outside the box it's obvious but are those resistors the right value? I've only done one mpu4 repair so I don't know them to well. Watching the thermal video they're getting very fecking hot... Where is the power going and is it related to the other IC getting hot? I couldn't really tell what's happening in the vid... just asking out of interest. 

Yes the resistor values are correct. They haven't been replaced either. They are being driven from IC14 and that is getting the signal from IC3. The draw will be from the MOSFETS being powered up continually. I doubt 8 Fets have all failed together so I would suspect it is a fault on IC14 or even IC3 or both.

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Are the Fets on the lamp circuit? I really don't know Mpu4 that well, is there a lamp enable line? Seems weird that that area whatever that area Is is enabled and driven aswell. Is the board coming out of Reset at all if not it may just be twitching in the dark.

I'm totally intrigued on this one I'm not going to lie. 

Is the cpu on a socket? 68b09p. Are the data lines all over the place?

 

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20 hours ago, Prototype_uk said:

Good advice thank you. Do these look genuine to you? 

https://www.ebay.co.uk/itm/274346525722?hash=item3fe053c41a:g:9q0AAOSwZDleov8~

They could be OK, I've dealt with them before with no issues. Genuine 'pulls' are normally good but with Ebay you always need to be suspicious. I thought you were looking for PIO's?

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On 1/12/2022 at 9:58 PM, Prototype_uk said:

Do you know if the PIA's are still available or would I have to get a scrap board for parts? I think I will try changing IC3 (EF68B21P) and IC14 (ULN2803A) Those resistors were getting mighty hot. 

 

This is brilliant 

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3 hours ago, midibob said:

They could be OK, I've dealt with them before with no issues. Genuine 'pulls' are normally good but with Ebay you always need to be suspicious. I thought you were looking for PIO's?

Oh are they not the PIO's? Sorry this is my first time at a repair. Can you point me in the right direction please?

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7 hours ago, MattyL said:

Are the Fets on the lamp circuit? I really don't know Mpu4 that well, is there a lamp enable line? Seems weird that that area whatever that area Is is enabled and driven aswell. Is the board coming out of Reset at all if not it may just be twitching in the dark.

I'm totally intrigued on this one I'm not going to lie. 

Is the cpu on a socket? 68b09p. Are the data lines all over the place?

 

Sorry I haven't got a logic probe so I can't' check any activity. If I had a working Test ROM that would be half the battle but as I said in my video which I made for midibob I don't want to blow my actual machines ROM (ANDY CAPP) which is why I got a second hand ROM off eBay to do this testing with this repaired board. Problem is it appears this ROM doesn't work so for all I know the board might boot if I had a working ROM. I might be over cautious but I don't want to blow my Andy Capp ROM testing this board. 

The reason why I am trying to get this repaired board running is to eliminate the problem I have with my machine which is it has stopped accepting coins. Magik said it could be the Switch Matrix and to try another board so I bought this MPU4 off eBay to repair and use for testing to see if it fixes the fault.

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3 hours ago, midibob said:

They could be OK, I've dealt with them before with no issues. Genuine 'pulls' are normally good but with Ebay you always need to be suspicious. I thought you were looking for PIO's?

DUH, I just realized these aren't the right part numbers. I've been working too hard of late :(  

How about these to replace IC3 - IC8? 

https://www.cricklewoodelectronics.com/6821P.html?gclid=CjwKCAiA24SPBhB0EiwAjBgkhpXJibcZo6dnPKz-1zNrRMCLsNNpYi5u_5VT7Hb380nBWp2jeGk2JBoCgFwQAvD_BwE

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12 minutes ago, midibob said:

Nope, afraid not. You need 68B21 which are slightly faster. Don't buy anything which comes from or looks like it might come from China! Some times Ebay sellers say they are UK based but they aren't. A lot of these are fakes so beware.

Third time lucky? 

https://www.cricklewoodelectronics.com/68B21.html

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