Hello Group,i got colt 485 black shadow ssb it has Cybernet chaise,friend i got from said that the AM transmit audio use to work then one day it quit,he told me while out driving around in car with new cheap ant,he said the swr might have been abit high how high i do not know,he said the audio start to get weak as he keep taking on it .When i key AM side it transmit a signal and it has great receive on AM and the ssb receives and transmit really good.
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colt 485 problem
- Thread starter awc
- Start date
Hello Sonar,thanks for replying back,yes that correct everything works except the dead carrier when i key the mic,when i speak there no audio.
if the mic works on SSB it should be just fine. I tried to find a schematic for this radio and no luck. was just wondering if it has a AM modulation trans like the 148 has if it goes bad it will throw a high carrier at times and no modulation. normally it is a 3 leg trans mounted to the side of the case.
I have never had one of these to work on so not much help here.
I have never had one of these to work on so not much help here.
It's odd that you're getting modulation on ssb but not on AM.
I'm sure someone who knows that rig will eventually Chime in.
I assumed the Modulation for AM, and SSB come from the same place on the board. Could be a bad componaint somewhere in the AM modulation chain. I'm kinda surprised no one else replied.
Give it another day. You obviously have knowledge, and I've little doubt that the problem will get rectified. Good luck. 73's
Hello Group,like 2 thank all of u for ur input on this matter, sp5it i can not fine that Q50, i do have a copy of the RCA Co-Pilot service manual that has same Cybernet chaise,the block diagram for the Am transmit does not have Q50.
The original 40-channel (ONLY) Colt model 485 dates to 1978. It's covered in Sams volume CB-227. Has a PLL02A pll chip. This is the "unlocked" type chip that was outlawed a year or so later. Made this radio popular for folks who wanted lots of extra channels easy.
The AM carrier is set by a big white ceramic power potentiometer. It's mounted on a bracket to the side rail, about halfway to the rear of the radio behind the channel selector. If it fails, you get no AM carrier. Simply turning the shaft a bit to see if maybe it is set to a "bad" spot on the resistance element is where I would start.
The two wires that connect to this control are a good place to test for DC voltage. Should have at least 12 Volts DC on one of the two lugs when you key the mike in AM mode. The other lug will have roughly half that, depending on the setting of the pot.
And if one lug shows zero volts, the control could have failed altogether.
Not a common thing to see, but not impossible.
73
The AM carrier is set by a big white ceramic power potentiometer. It's mounted on a bracket to the side rail, about halfway to the rear of the radio behind the channel selector. If it fails, you get no AM carrier. Simply turning the shaft a bit to see if maybe it is set to a "bad" spot on the resistance element is where I would start.
The two wires that connect to this control are a good place to test for DC voltage. Should have at least 12 Volts DC on one of the two lugs when you key the mike in AM mode. The other lug will have roughly half that, depending on the setting of the pot.
And if one lug shows zero volts, the control could have failed altogether.
Not a common thing to see, but not impossible.
73
Always giving excellent advice nomadd.
But he's got receive and modulation on ssb. Receive and a carrier on AM. But no modulation while in the AM mode. So everything is working with the exception of AM Modulation. Are there separate components for Modulation on SSB/AM?
What would be a reason for have modulatiion on SSB and an AM carrier, but no modulation on the AM mode?
Thanks psycho and the rest who took interest in my repair project,i hope 2 fine a answer as well on here.Again thanks 2 all for input on this matter.73s for now.
Hello Group,like add some info from the block diagram of the AM transmit section,do u think of these might be my problem is it RF amp Q7 or RF pre driver Q8 or RF driver Q9 or RF power amp Q10, there more 2 the block diagram,any 1 input be nice thanks again group for help from before, this what being on here all about helping one another thats how we all learn from 1 another. 73s for now