ARII 5v outputting 14v..?

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Question for the PS gurus...

I have an ARII-02 PCB that's outputing 14v on the 5v line...sense mod is in place...everything else is outputting normal voltages. The adjustment on the AR2 barely makes any difference (maybe a hundredth of a volt)..and swapping the 2N3055 seems to not make a difference. Also swapped out the LM305...and TIP32...no change.

Is there any clever/scientific way to trace what's going on... perhaps removing something and seeing if voltage still appears (perhaps a shorted line?). Measuring another test point...etc?

It's driving me slowly insane as I'm reading 101 'shotgun all the parts' postings...and that's already been done...nothing's cooked. Some really great parts identification sites out there that have really good basic detail as well. I do have another AR2 board that's working fine and compared it, and everything is installed properly, nothing seems out of sorts.

Any ideass are appreciated...

Thanks
Pete
 
At lease one of the following is likely the case (in decreasing order of probability, highest first):

- The 2N3055 is bad (big transistor in middle of heatsink)
- The LM305 regulator is bad (8-legged can-looking thing)
- The TIP32 is bad (square transistor on heatsink, closest to the LM305)
- One of the diodes is shorted (possibly also causing any of the above)

All but the LM305 can be checked with a DMM, pretty easily. Google transistor testing if you don't know how.

Also,note you should remove the 2N3055 to test it, as you can get misleading readings measuring it in-circuit. All you have to do is desolder the 2 pins, and remove the two nuts, and you can pop it free. You don't have to desolder the screws themselves.
 
Andrew - thanks for the detail. I fixed the issue. It ended up being CR4, the 1N4002 diode was cooked. It didn't catch my eye originally because it was black just like a diode, but it was originally clear...removing it made it shatter into a million fragments and everything started smelling like burned electronics :) I swapped in a new diode, and everything checked out - no more 14v, right back at 5.15v

I ran through tests on the 2N3055 earlier (out of circuit) and was having a problem with my other AR2 where it was actually testing out as ok, and in circuit it was outputting 5v, but when I put a board on it, it would drop down to under 1v. I had the sense mod in, so i was thinking the board was causing the issue...since it was only dropping below 5v when it was connected to the board, but when I swapped with a new 2N3055, everything was back on track and I got 5v with the board plugged in as well.

It's been a fun week with ARII's :)

Pete
 
Sweet. Glad you were able to find it. I should have said 'bad diode', as they can open as well as short.

And yeah, the 3055's can be tricky, which I've learned the hard way. They can fail in a bunch of different ways besides shorting or opening, including testing ok with a DMM, but behaving weirdly when powered and under load. I've seen them cause the AR to output 5V when measured without the board, and then drop to 1-2V once the board is plugged in.

I've also even seen cases where they will be ok under a light load, but then fail under a heavy load. As a result, I always bench test them with a full 5-amp load, which is about the most any game PCB will draw (except for Pole Position, which draws around 7-8 amps, but this is why PP uses two ARs).
 
Ok, good to know - yeah.. will have to keep that in mind. Do you just load it down with a fairly heavy resistor to pull that 5a?

I had a Pole Position once....once..:) Lost track it had two AR2's... sounds like a blast :)

Pete
 
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