How fried is this maxtrac?

nmfire10 · Post by **nmfire10** » Wed Jul 05, 2006 6:18 am

I think I hooked up the IGN SENSE to the wrong accessory pin on this UHF maxtrac (16-pin model). About a minute after it was plugged in, there was a loud pop and a large amount of smoke pouring out the radio. (never a good sign).

I opened it up and there is a big electrolytic capacitor that blew up. It is mounted horizontal on the board and very prominent. This appears to be the only thing that got fried. What are the chances this thing is repairable?

kcbooboo · Post by **kcbooboo** » Wed Jul 05, 2006 6:40 am

Probably pretty good. Do you know what pin you DID hook +12V up to, as that will let us trace the circuit back and figure out if it wiped out anything expensive.

Dave or I can try to fix it.

Bob M.

jackhackett · Post by **jackhackett** » Wed Jul 05, 2006 7:06 am

That should be the DC blocking cap on the output of the audio PA, you must have hooked it to speaker +
If you're lucky it just blew out the cap, if not the audio PA might be toast. The easiest way to test would be to cut out the bad cap leaving a bit of the leads, then put another cap across the leads and see if you get speaker audio, probably any large value cap, 100, 220, 330, or 470uF should work for a test, negative side goes towards the back of the radio IIRC. If you get good speaker audio, take out the board and replace the cap with the proper replacement and you should be good to go.

nmfire10 · Post by **nmfire10** » Wed Jul 05, 2006 7:47 am

Well, now that I'm looking at the pinouts for both radios, I'm still confused. I took the acessory connector from my old GTX and put it on the maxtrac. The GTX and the Maxtrac both use pin-10 for +12 ignition sense.

The only other thing was the GTX internal speaker jumper was in place. I think it went from pin 13 to pin 16. On the maxtrac, 16 is also speaker + but 13 is "SW A+ Sense". I don't know what that is supposed to mean.

kcbooboo · Post by **kcbooboo** » Wed Jul 05, 2006 8:11 am

Well, the first thing you now know is that you can't just unplug the accessory plug from a GTX and plug it into a MaxTrac, or vice versa. Put the plug back into the GTX and add a label to it so you don't do this again.

I'd guess that at a minimum the 1000uF cap is now dead. It probably saw +14V on the negative end and +6V on the positive end and let out its lifetime supply of smoke. It most likely shorted out, and might have taken out a couple of transistors as well. Still it should be repairable.

Send your letter of appreciation to Motorola, thanking them for making all these radios use the same accessory plug but wiring it rather differently in the GTX.

Bob M.

jackhackett · Post by **jackhackett** » Wed Jul 05, 2006 8:22 am

Hmm.. I'd forgotten what value that cap is.. been too long since I've looked at a maxtrac that closely ;)

SW A+ Sense basically is A+ after the power switch, generally used to power accessories such as a remote adapter that you want to power up with the radio.

Whatever idiot at Moto came up with the idea of changing that pinout should be fired.. oh wait, he's probably been laid off and his job moved south anyways..

nmfire10 · Post by **nmfire10** » Wed Jul 05, 2006 8:36 am

So I basicly sent +12 right into the speaker circuit. Greaaat.

I'll try replacing the capacitor and see what happens. If it needs more help than that, I know where to find you, Bob... (or dave).

kcbooboo · Post by **kcbooboo** » Wed Jul 05, 2006 8:50 am

For the benefit of whoever gets the radio (to fix) after you, please be careful when removing the bad capacitor.

You can probably get something that will fit at Mouser or Jameco. Go for the same or smaller physical size that's 1000uF at 16 or 25 Volts.

Bob M.