maxtrac 300 serial port problem

fredv · Post by **fredv** » Sun Jan 28, 2007 9:21 am

I have a UHF maxtrac 300 D34MJA77A3CK and while attempting to reconnect the 2 connecters from the controlhead to the radio, I believe I smoked parts that control the serial interface to the RSS. And yes the power switch was off but the power supply was still on and connected (I know, I know........)Anyway, the radio works fine except when trying to program it. The RSS fails to connect to the serial port and aborts. I had programmed it earlier and all went well. An identical radio programs fine. So, am I correct in assuming I have smoked certain parts on the logic board, and how who or where can I get it fixed? Thanks FRED

Max-trac · Post by **Max-trac** » Sun Jan 28, 2007 9:42 am

You are lucky the programming is the only problem.
I would look for a burned trace, that might be repairable.
If you know what connections you crossed, you could trace it back.
If you smoked something in the brains, the eaisiest fix is to get a cheap 800 radio and steal the logic board, (blank and initialize).
(you can do a search here for the proceedure).

fredv · Post by **fredv** » Mon Jan 29, 2007 7:53 pm

Thanks. I will trace it out. do you know which chip(s) are used for the serial port.

fredv · Post by **fredv** » Mon Jan 29, 2007 9:13 pm

Well it looks like I sent 12 volts from pin 6 on J8 to pin 7 which is the SCI. I believe there are 2 transistors in push pull(?) directly in the path starting from pin 7.
If anyone knows there value or if the IC on the other side is part of that same circuit please reply.

Max-trac · Post by **Max-trac** » Tue Jan 30, 2007 9:38 am

I looked on the schematic for the 5172 logic board;
There is a 10v zener to ground on that line, probably took that out.
You should see 5v on that line.
It goes to 2 transistors and to IC U601B.

Which logic board is it?
Send me your email;
I will send you a jpg of the area.