The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

I got a free radio last night that is not working, removed covers and found
burnt up voltage regulator part #L78M08CV, when powering up radio
with the bottom board near the front of the radio removed, chip#2902N
gets very warm is this because i have no voltage regulators. or do i have more problems? i can not get any parts untill tomorrow. thanks any help would be great!!! kevin from
colorado

ONE UPDATE..... I just found foil in place of the fuse thats nice. any help would be great thanks. kevin

it sounds like it has been reverse wired, you will need to replace a few parts, the main regulator on the chassis side rail, both regulators on the cpu pcb, the audio amp ic, and the 2902, then you may find that it wont rx/tx, or the cpu will be fried, if your lucky the cpu is ok, th final and driver will be fried too, and has probably burnt out the trace that supplies DC to them.

I have fixed several reverse wired HR's, sometimes it is a big job getting it up and running again, sometimes it almost isn't worth it.

what is the part number for the audio ic chip? is there a way to test the voltage regulator or am i just better off replacing all off them.thanks alot for the help!!! cant wait for the stores to open tomorrow to get some parts!!

The reverse voltage would have gone right through the radio (otherwise the regulator would not have blown), so it is best to just replace everything that would have been subjected to it (better to replace it now for a little bit on $$ than risk further damage, or blowing new parts).

The audio amp looks like an IC, it is located at the left side towards the rear, and has a small copper heatsink sticking up from it which is soldered to the PCB, I cant remember the number of the top of my head right now.

i have a extra radio i pulled the topped board out of an installed it in my junk radio. the radio meter is pegged, but it does transmit very low power. no rec at all now the 2902n chip is not getting warm. the part number on the side rail voltage reg is HA17808 and i have a L7808c-v can these be crossed? the display is working just really low rf power and the meter is pegged all the time unless i key the radio. thnaks alot for all the help.. kevin from colorado

The meter is pegged because of the 2902 being blown, replace it and it will fix that fault, it may even fix your RX fault.

You can replace the 7808 with any other 7808 device of the same package.

If you end up not needing the junked MPU PCB I could use another one to repair a radio I have here, in case you are interested in selling it once your radio is fixed.

ok scott i will let you know on the board!! thanks for all the help. i just replaced the side voltage regulator and tested still same problem. so tomorrow i will try to get new chip! the part number was L7808c-v hope thats ok. thanks again!!! kevin from colorado

I saw this thread when trying to find what is going on with my 2510. First off this radio was hooked up backwards by my Dad. I replaced the audio chip & the 2SC2166. There also was a trace that was burnt. Fixed that trace. Radio is working. When I key up. The dead key is sparatic. Sometimes I will get a high dead key. Sometimes a low deadkey. Then sometimes when I key it. The deadkey will be a lil high & as I am holding the key. The watts just start dropping. Like it will key 8 watts & then start falling down to like 2 or 3. Sounds like a bad cap or something? thanks

You will need to replace the final as well, it is very likely that it has been damaged, they rarely survive being reverse wired.

The finals in it now seem to test fine. I did replace the 2166, because it was the only one that seemed affected to the reverse hookup. When I was turning the am power up. It shot up to around 35-40 watts. But so did the dead key. And then I turned it down. I like the higher watts, but I need a lower deadkey. So I think the mrf477 is fine. This is what i got when trying to align the the finals tho.

I am getting no reading on TP4+ to TP3-. And On TP4+ to TP2- getting a 32.5ma.