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Hi folks. I finished my board and switched on the power but zero leds came on... 

Seems like there's no power. I've heard about the mpu switching on the psu?

Just seeking some advice slightly confused as I don't know the tech to well.

 

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M1A all finished and the machine back to life. 😎 20200313_105646.mp4

key to maygay is test the RAM pins with a logic probe while there is no card in.  They should all be floating (not HI or LO) .  If any are showing a signal theres a shorted IC on the databus. Sec

Here's two of my latest boards I've repaired while off work furloughed. Both were not to bad battery damage really.  One had burned out track under the meter driver which I've not seen before...

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If you have removed the capacitors chances are you pulled the through hole copper out of the holes to so they no longer make connection from the top of the board to the bottom, caps rarely need changing in M1, Its usually the bridge rectifier that starts to fail rather than the caps, I bet if you measure the removed caps capacitance they will be fine

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That's useful information thanks. I've not removed the large caps yet I'm doing some research before hand. With my other techs I accumulate Psu's so I've never actually repaired one!

I've found a fault on Diode D1, I'm getting a reading both ways on that.

The bridge rectifier on the board I'm not sure how to test yet. It goes up slowly because I presume it's charging the caps? So I'm unsure of how to read it. The relay looks ok visually.

I'm up for doing this though.

Apologies for the lots of questions I was psyched up to test my board this evening. Is there a schematic for the psu? I'm searching for the diode ID and other ID's

Also when you guys replace the loom psu connector block to the mpu. What type do you order?

There's nothing better than learning all this stuff! Thanks fellas 😊😎

 

Edited by MattyL
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Yeeeeeaaaaaaahhhhh!

I've got it running!

Came back to the psu tonight, the power fault on the was a broken 5v volt fuse holder...the thread was knackered. Tested it and found it supplies 5v if it's pushed in haha!

Pushed it and my board fired up. It's running now great but now its the waiting game to see if the board holds up 😎

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Edited by MattyL
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10 hours ago, warlord said:

Lets hope it works and dont give you greif,maygays are like gorgeous women,high maintenance.nice machine dude and well done

Haha yeah they're also welcomed on my bench.

Thanks mate 😎

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Hi folks... I'm still having a few issues with this M1B PSU. What happend the 5v fuse blew now there's an initial supply of 5v there which then drains down to 0vDc within 20/30 seconds of power on.

I suspect that also causes the 12v relay to not be switched because the main board power drops off so quickly.

Does anyone have any ideas? I can replace everything back from the 5v pins but would be nice to know what's happening.

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Yeah cheers mate. This time I did replace the bridge rectifiers also replaced the big 5v cap(cut it off) and smaller caps... also the did the diode too and the 5v fuse holder. Finished it at 1am last night.😎

 

It's back up and running now... phew. Totally sweating the board was ok!!

It's the first psu I've done so I'm happy I need a spare though I'm not used to having so little spares. Hopefully I've got one lined up.

 

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Ok so now I'm up and running again I thought I'd give the Maygay test Rom a try. I tried it in my board while hooked up to the machine and all board LEDs remained solid on. Everything is running ok so I must be doing something wrong?

I copied them onto a TI/ TMS 27C010A which was the same Eprom as the game Rom. Tried them onto the green 1993 Esp card. Any ideas anyone?

 

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