Hello everyone, this is my 1st thread, it's going to be more question with a small introduction.
All of my radios were either given to me, or purchased for a few dollars. They were mostly basket cases that were replaced by something more modern and some from retired Truckers. Every time I recieved a radio I knew it had issues that would need addressed, Sometimes I like the "tinkering/testing" part of the hobby more than talking on air part. These issues are usualy common things like a reverse polarity diode, conectors coming loose, smoked output transistor, dirty switch/pot or just out of whack due to the trimmers and cans being screwed with. Every now and then I'll get something that operated normally, I still like to make sure they operate to the best of their ability and are on frequency just like the others after the repairs.
Recently I recieved a "Cobra 29 LTD Chrome", The owner said it wouldnt shut off, Keys up but doesnt transmit and recieved just fine. It spent the 1st half of its life in a gravel truck with no windows. After I cleaned it up in and out with electrical cleaner and a little work on the switches and pots on the front panel, I had a working radio. Most of the issues were due to dirt and moisture. My meter only shows 3 or so watts into a dummy load, so I begin what I call my "mini align" it goes like this:
1: Scope on resistor near front of IC2, peak L22.
2: DC meter or scope on DC 1to1 gradient on R88, channel 40, TXing, L19 to 3.2v.
3: Scope on jumper between L18 and L4 or resistor above L4, peak L18.
4: Scope on R61, peak L20 and L21.
5: Watt/Mod meter into dummy load, 1000hz tone on phone (adjust volume/distance for near 100% mod on meter), TXing, adjust L23, L17 and L14 for greatest output on watt meter.
6: Frequency counter on output into dummy load, TXing on 19 or 20, Adjust L24 to correct frequency for desired chanel and doube check 1 & 40 just to be sure.
This has worked for every cobra 29 I've popped the bottom cover off of so far, except for two. One I will ask about today and the other might get a claw hammer if I look at it any time soon. If anyone has any pointers or corrections for the "mini align" Please chime in, I'd hate to leave misinformation for others to stumble across, plus it might answer my question.
I don't feel that I have the right equipment or experience to do a recieve align yet, thats for another day.
The radio was tweeked in like above, will deadkey around 5 watts on my antique Micronta 3 window meter and gets 100% modulation with maybe a 1/2 watt upswing while speaking normaly into the mic., but when I return the bottom cover it will backswing to 3 watts and only gets to 60% modulation. With the radio upside down I can put the righthand side on while tilted up on the left and there is no change, but the lefthand side will cause the above issue. Remove cover/all is fine again.
What do you feel could cause this?
I'm going to mess with it more tomorow, as I'm off work for a few days.
All of my radios were either given to me, or purchased for a few dollars. They were mostly basket cases that were replaced by something more modern and some from retired Truckers. Every time I recieved a radio I knew it had issues that would need addressed, Sometimes I like the "tinkering/testing" part of the hobby more than talking on air part. These issues are usualy common things like a reverse polarity diode, conectors coming loose, smoked output transistor, dirty switch/pot or just out of whack due to the trimmers and cans being screwed with. Every now and then I'll get something that operated normally, I still like to make sure they operate to the best of their ability and are on frequency just like the others after the repairs.
Recently I recieved a "Cobra 29 LTD Chrome", The owner said it wouldnt shut off, Keys up but doesnt transmit and recieved just fine. It spent the 1st half of its life in a gravel truck with no windows. After I cleaned it up in and out with electrical cleaner and a little work on the switches and pots on the front panel, I had a working radio. Most of the issues were due to dirt and moisture. My meter only shows 3 or so watts into a dummy load, so I begin what I call my "mini align" it goes like this:
1: Scope on resistor near front of IC2, peak L22.
2: DC meter or scope on DC 1to1 gradient on R88, channel 40, TXing, L19 to 3.2v.
3: Scope on jumper between L18 and L4 or resistor above L4, peak L18.
4: Scope on R61, peak L20 and L21.
5: Watt/Mod meter into dummy load, 1000hz tone on phone (adjust volume/distance for near 100% mod on meter), TXing, adjust L23, L17 and L14 for greatest output on watt meter.
6: Frequency counter on output into dummy load, TXing on 19 or 20, Adjust L24 to correct frequency for desired chanel and doube check 1 & 40 just to be sure.
This has worked for every cobra 29 I've popped the bottom cover off of so far, except for two. One I will ask about today and the other might get a claw hammer if I look at it any time soon. If anyone has any pointers or corrections for the "mini align" Please chime in, I'd hate to leave misinformation for others to stumble across, plus it might answer my question.
I don't feel that I have the right equipment or experience to do a recieve align yet, thats for another day.
The radio was tweeked in like above, will deadkey around 5 watts on my antique Micronta 3 window meter and gets 100% modulation with maybe a 1/2 watt upswing while speaking normaly into the mic., but when I return the bottom cover it will backswing to 3 watts and only gets to 60% modulation. With the radio upside down I can put the righthand side on while tilted up on the left and there is no change, but the lefthand side will cause the above issue. Remove cover/all is fine again.
What do you feel could cause this?
I'm going to mess with it more tomorow, as I'm off work for a few days.
