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

I have another Cobra 148, Had a terrible clarifier unlock job done to it:

PC-412 Board
PLL 8719

MB3756 pin 1 should have 8 volts, just as pin 3, but this radio is a 13.8 on pin 1. Is the chip bad? It had a very weird clarifier mod, I am putting it back to stock , and noticed pin 1 was high. ( The mod was attached to pin 3..... Bad , I know)

Should I replace the mb 3756? Thanks in advance!

There is another thread in this section which shows the correct voltages for the device (active within the past couple of weeks), just cross check against that to confirm your readings.

if any output from the device is not correct it is likely that the device has failed, BUT first check that someone hasn't done something stupid and connected another supply to that rail by mistake when doing any mods.

Thaks Scott, I did look for a thread, must of missed it. I did lift pin 1 to see if there was voltage on the board, there wasn't . 13.8 coming from the chip.
I don't have a spare, but I'll pull one from a working radio to test.

Only problem noticed so far, audio real distorted, and on SSB there is a pitched squeal on RX when volume is turned anywhere above the very lowest setting. Squeal seems to be in volume circuit, not an actual RX signal coming in.

Thanks again!

It may be that the radio is trying to TX and RX at the same time, replace that IC and see if that fixes the problem.

Thanks again Scott,

I pulled a good one out of the other 148 and put it in. All problems went away. In fact to get it on freq before, I had to bottom out L23 to get AM right. Now I had to realign it and the L23 slug is back to around center.
Audio is great on AM and SSB again.

Freq also climbed about 8Kc's as it was warming up, this time it was steady, only about a 1 Kc jump.

Now if I can can just fix the F model in the other post!!!!

Thanks Again!!!!!!
73's