Spectra A7 power issue

[W8CLA]

Hey guys,
I picked up a Motorola Spectra A7 at a hamfest and everything seemed to be working fine until I hooked up a speaker. I pulled the control head off of a MaxTrac to borrow the speaker but upon turning on the power the LCD light up with the seftest and went dark.

If I disconnect power and the reapply I can hear the start up tone but nothing from the control head. However if I let it set with power disconnected for 5 minutes or so it will lite up the front for a few seconds and go dark again.

Anyone have any idea as to what I've done? Thanks

[Karl NVW]

Two c0ommon possibilities:

1) The speaker leads of the Spectra are both isolated from ground. A MaxTRAC speaker feed has one side grounded to chassis. If you had any grounded lead connected to the MaxTRAC (including the antenna connector) you probably fried the audio output stage.
... OR ...
2) It could be the perennial bad electrolytic capacitor problem.

If you tested the unit before you bought it and it had clean audio then, expect #1. If the audio sucked, it's probably #2, and you can expect many other intermittent issues until you re-cap the radio.

[W8CLA]

Thanks for the advice Karl. Unfortunately I didn't test until I got it home, just a quick power up without any speaker just to make sure it light up. I bought a MaxTrac a few months ago and it popped the fuse as soon as connecting power.

I had the control head completely removed from the MaxTrac so there wasn't any chance of anything being grounded. I pulled the caps off the control head board and there was definitely signs of leaking so I'm going to recap the whole radio.

Thanks again and 73

[Jim202]

I know this is an old post, but you may have a radio with a sorted reverse polarity diode shorted.

This diode was designed to protect the radio from being connected backwards to the DC source supply. They normally are a good sized diode on the board.

If you have the service manual, it should be easy to locate.

Jim