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Fried a Grant XL...

U

ultanium

Member
Nov 15, 2012
5
0
11
Picked up a really clean Grant for $25 from an abandoned storage room. I hooked it thinking nothing could possibly be wrong with it, but it smoked out. Pulled the covers & found wires melted to the noise blanker & more. The radio still powers up, receives signal by watching the meter, but nothing comes out of the speaker. I also tried an external speaker but no joy. I'll replace the melted wires and the two chokes this weekend, but are there any other components I should check or replace?

Tom
Black Sheep 228
grant1.jpg

grant2.jpg
 

I know this sounds stupid, but did you hook a mic up to it? It won't play the receive through the speaker if you don't.

Hope you get her fixed, they are great rigs!

73,
RT307
 
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Yup, needs a mic plugged in for recieve to work. It would be well worth sending in to someone like DTB Radio and just get it fixed & tuned right the first and last time.
 
From what can be seen from the pictures, those chokes at the power plug are usually fried when there is a dead short on the board or the radio's main power wires were hooked up backwards. If the protection diode was removed and you powered it up with the wires reversed; then that radio is close to 'toast'.

You will need to look at the schematic (found on 'CB Tricks') and replace the first diode closest to the power plug (called the 'reverse voltage protection diode' - for reasons that are obvious by now).

IS that long wire that fried in the center of the photos - have three conductors in it? IIRC, that is the noise blanket circuit switch wires that goes to the front of the radio. It does not carry 13.8v to fry like that. Really is hard to diagnose your problem from a picture on a forum.

Start the troubleshoot from where the power comes in the radio and work your way in. The use of the schematic is ESSENTIAL!

If you haven't done this before, then either take your time and learn to fix it or pass it on to a tech that can sort it out and do it for you.
 
Last edited:
Got home and read all the replies, you guys are quick! Plugged the mic in and bingo, there's audio now. The 3 wires in the brown cover do go to the nb switch, and no the radio was not hooked up backwards. That being said, I will double check the power cord that came with the radio (cig plug to 3 pin) and see if the PO wires it backwards. Hooked to my antron right now, and it looks like she's gonna live.

Tom
Black Sheep 228
Houston, Texas
 
Yeah, you would think I would have learned that by now :) I did check the original power cord today, it was wired correctly but had a 15A fuse! As near as I can tell, the radio is still working (I yanked power from it when it started smoking), one tough radio. Also picked up a semi-dead 2950 for $10, think it has power supply issue (dimly lit backlight but no readout on the display), and a working Magnum 257 without a mic for $75. I may have to put my Golden Eagle MkIV up for sale if this keeps up, I need more room!

Tom
Black Sheep 228
Houston, Texas
 
Good question. As far as I can tell, the 1135 on the back panel is shorted and thanks to the 15A fuse, the damage was done. It looks like the 1135 is also a part of the noise blanker circuit, and that explains the wiring to the NB switch also being melted. I searched the forum, and it seems the 1135 is prone to failure and is commonly replaced with a TIP-31 or NTE part.

Tom
Black Sheep 228
Houston, Texas
 

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