I'm working on a MPU 200 for a friend. I replaced the transistors (Q1, Q2,Q5), new U8 socket and a few capacitors in the corrosion zone. Overall it's was in pretty good condition.

When I connected my power supply I thought I was getting nothing on the LED. Then I shaded it with my hand and I saw it was flashing but the LED is very weak. I'm getting 12 volts on both sides of R29 - which makes me believe I'm getting the proper voltage to the LED.

Can a LED go bad and still flash (weakly)?

Also what's strange is I'm getting 2 flashes then pause - then 1 flash and pause - then 4 flashes. And I don't have 43 volts connected - and the first flash don't seem to be a flicker - looks like a real flash.

Thanks Jack, I did clean and check the traces in that area and they seem to all make good continuity.

Sounds like the R29 and the LED need to be changed - I'll do that and try again.

I thought I could ground the transistor to test the LED but which leg is the collector. (I know just enough to be dangerous).

Thanks

Bob

Thanks Jack - you were right - the LED was going dim. I changed the LED and R29 and it flashes nice and bright now. (but still have 12 volts on both sides of R29)

But I'm still getting 7 flashes without 43 volts connected.

2 flashes and pause
1 flash and pause
4 flashes

And the first flash is not a flicker - it's as bright and long as the second flash.
This doesn't seem right.

Any suggestions?

Thanks

Bob

Actually the LED appears (to me) to be off after the last flash.

I have a 24 volt transformer with rectifier that I used before to check zero crossing before. I'll hook it up and check.

If you're correct (and I think you are) I should get 5 flashes after the last pause? And if I do then all is OK?

I'll let you know how it turns out.

Thanks for your help.

Bob

Unfortunately I don't have the game here (just fixing the board for a friend) and I don't have the connector headers installed yet. So I can't test it in a game.

However, I just tested it with my 24 volt transformer and I now get 8 flashes - so I'm thinking the first flash is just the flicker.

Looks like we fixed it - thank you so much for your help.

Bob