Motorola spectra help

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k5rpd

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I am having a problem with a Motorola Spectra. I have a vhf analog with an A5 head that is working with no problems (P/N HLN6337D). I also have an 800mHz analog model with an A5 head (P/N HLN6075D) that will not power on. The power protection diode was ok. The small green fuse on the control board was ok. I had power into the DB15 plug for ignition sense. So I checked the circuitry of the two control heads (visually) and here is what I found:
On the attached pictures I labeled the Damaged one and the Not Damaged one. The unit that will not power on was obviously damaged. This is right behind where the power button makes contact with the board to turn on the radio.

Has anyone seen this damage before? Thoughts on repairing vs. replacing?
good_a5_spectra.JPG damaged_a5_spectra.JPG


Going to use the to monitor here locally in Russellville!
Thanks,
JJ Smith
K5RPD
 

jim202

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New Orleans region
The componets in that corner are part of an ignition sense circuit that feeds U4 pin 42.
The burned component area contains 4 capacitors, one resistor and 3 diodes.

The circuit has the A+/IGN come in through R3 (22k) resistor. The other side of the
resistor feeds the U4 pin 42 and 3 diodes in series to the gate of Q51. This feeds
or generates the SWB+ line.

I suspect that this Q51 FET is not turning on. You would just have to mess around and
see if one of the diodes is open or shorted.

2 of the caps go to ground on one end. The other cap is across 2 of the diodes.
All the caps are 0.01 uf.

If all else fails, you could add JU007 which will provide SWB+ any time you get
an IGN voltage.

So I guess the best place to start is to see if you have the SWB+ coming up with the
PWR switch being pushed. If not, you could add the JU007 and make the problem
go away. Just remember that the Q51 still needs to function.

Jim
 

k5rpd

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Joined
Mar 7, 2006
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Location
Springfield, AR
..

Jim, Thanks for the wealth of info you provided.
I am going to clean that area to see what it looks like under the charred or burned looking area.
You wouldn't happen to have the component layout handy for the HLN6075D A5 head would you? And be willing to snap a pic of that area of the board for me?

Again, thanks for the information!

JJ
 
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