Ultimate problem

kinrat · Joined: Jul 27, 2010 Posts: 4 Location: UK

Wonder if anyone can help with my next step at fault-finding my SL Ultimate.
I have a short circuit between -12V and ground somewhere on the pcb. I've checked the obvious, no bridging tracks or leads, isolated the panel wiring so it is not there. I've spent 2 days looking for this through a magnifying lamp and I still can't find it.
My final solution is to cut the ground track at several points and reconnect them one-by-one until I can narrow it down to a single area. Is there anything else I could try before this?

blue hell · Posted: Sun Dec 12, 2010 10:12 am Post subject:

kinrat

Yeah there are some tricks ... but its a nasty problem once the board is populated ... if you still have some voltage and the power supply does not over heat on it you can try to trace it with a (milli) Volt meter ... the nearer you get to the short the lower the voltage would be ... another one is to hope its a small short and apply a lot of current to burn it out ... always tricky though Rolling Eyes

(and you need a good power supply of course).

th0mas · Joined: Feb 27, 2010 Posts: 12 Location: Ottawa

Check with a multimeter on it's most sensitive setting

Is there any resistance between power and ground at all? Absolutely 0 ohms? The closer to 0 the stronger the short. You may be able to use this to determine if it's a strong connection or a burnt out capacitor or something more indirect.

... I think. I'm not really that great with analog electronics Wink

Can anyone add to this? An engineer at my work fixed my laptop motherboard and was watching the resistance between power and ground as he cleaned up the carbon that was acting as a resistor bridging power & ground

blue hell · Posted: Sun Dec 12, 2010 5:38 pm Post subject:

th0mas · Joined: Feb 27, 2010 Posts: 12 Location: Ottawa

ew, it wasn't from smoking Smile

.. well, aside from magic smoke when I first applied power.. I replaced the dc input jack and there was a slight bridge that turned to carbon when I applied power. Amazingly this laptop works fine after he scraped away the carbon. Using it right now.

kinrat · Joined: Jul 27, 2010 Posts: 4 Location: UK

Thanks for your advice guys, I looked around the area with the lowest voltage on the negative rail and found the fault (eventually)
All works and getting some nice square and saw waveforms on all 3 oscillators, now just have to setup and tune it.

Thanks again Very Happy

blue hell · Posted: Mon Dec 13, 2010 4:06 pm Post subject:

good work