Penrose shutting down

Lostintime

Hi all,

I recently built my second Penrose from a kit.  The first one, that I built a couple months ago, works great.  The second one works fine when first turned on, but after a few minutes it stops working (lights out).  If I restart it immediately, it will shut down after a second.  If I let it sit for a while, it will stay on for a couple minutes before shutting down.  I noticed that the voltage regulator gets very hot.

So far I've  tried reheating all of the solder joints that I could reach without removing the front panel.  This did not change anything.  

Does anyone have suggestions where I should look for the problem?

Altitude

5V power rail short.  Your voltage regulator is overheating and shutting down as a result.  You can start by pulling the boards apart and powering it, if it still gets super hot, its on the main board, if not it's on the button board

Lostintime

Thanks.  I'll try that tonight.

Lostintime

I've isolated the problem to the main board.  I did so as suggested by Altitude.  I also double checked by swapping the boards between the functioning and nonfunctioning units.  I also separately swapped the ICs to make sure none of them were the problem.  

Now the problem is, I can't find a short.  Using a multimeter set to measure resistance I've gone contact by contact looking for differences between the functioning board and the non-functioning board and I can't find any differences.  

What should I try next?

Altitude

Its going to be tough without the board files but looking at the schematic, you can start by looking around the power pins for each chip (i.e. anything that connects to +5) , chances are there is a solder bridge somewhere

Lostintime

I've done that and found nothing. Also, I don't measure any shorts with the multi-meter.  I'm thinking that one of the components is probably defective and causing a short when it warms up.  Does this sound plausible?   If so, how would I go about finding the defective component?

Altitude

The odds of an actual bad part are very slim.  Post some high res pics of the mainboard, component and solder side

Lostintime

I appreciate your help.

Altitude

hmm.  soldering looks tidy.  When you pull all the chips off, what the resistance between +5 and GND?

cj55

What's the actual resistance between +5V and GND? Can you compare it to your other modul you built a couple month ago?

Lostintime

4.23k +5V to GND on the nonfunctional module.  4.29k on the functional one.  I think the problem is not a direct short. Something must be causing one of the ICs to draw too much power.  It takes several minutes for the module to shut down when started from completely cold. 

zorgo

Hey Lostintime,

I have the same issue. Did you ever figure it out?

Thanks

julian

have you checked the polarity of the tantal cap next to the DAC?
I had one penrose here for repair where the tantal was inserted the wrong way round and it resulted in an overheating and shutting down 78L05.

Lostintime

Thank you Julian.  It seems that a backwards tantal was the problem.   I destroyed the capacitor when I removed it and replaced it with a 10uF 16V electrolytic cap I had on hand.  Is this substitution likely to cause any problems?

zorgo

Hey Julian, mine pretty much had equal legs, but I see a small +16 text closer to one of the legs, is that the positive one? In layman's terms: should the text on tantal (marked 106) be facing the IC that it's next to? Currently mine is facing away from IC.

nightworxx

Yes, the plus sign marks the positive leg.

zorgo

Thanks night and julian. Flipping the tantal did the trick.