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89xlr
- Thread starter Ben Hebert
- Start date
TR14 is the sensing transistor for the modulation limiter circuit. The trimpot VR5 that's connected from the base of TR14 to ground sets the modulation limit.
TR15 is part of the "compression" circuit for the mike-preamp chip IC2. Serves to boost the preamp's output and feed it back to TR16 and hold the preamp chip's output level below its distortion point.
The phrase "not working right" covers a lot of ground.
Maybe what is 'working wrong' would be a more-helpful description of the problem you seek to solve.
73
TR15 is part of the "compression" circuit for the mike-preamp chip IC2. Serves to boost the preamp's output and feed it back to TR16 and hold the preamp chip's output level below its distortion point.
The phrase "not working right" covers a lot of ground.
Maybe what is 'working wrong' would be a more-helpful description of the problem you seek to solve.
73
I replaced tr14 but still no good. And I replaced th vr on the power supply board board but it's not the 13.8v I need
Can I use resistors for the power supply board.. does tr14 and tr15 is on the tx side of the radio?
I will mail you a proper VR to put in if need be, my thinking tells me it is not the VR anyways.
Replace TR15 if you can.
(As far as I recall, without pulling out the schematic again)
The section of the area of the radio deals with audio, if you have a diminished microphone input gain throughout the radio you may or may not be able to notice the difference in the way PA mode functions with the reduced gain but I can tell you from experience on a 89 XLR did had a few blown transistors in this very area once it was repaired I had to turn the microphone gain way way down otherwise the PA mode would blow my ears out, oh yeah and the modulation picked up to the point where I could talk on the radio... It is still talking on the daily, knock on wood!
It is running as it should to spec of the F.S.M. minus RX input sensitivity and alignment.. Need more gear lol.. 73
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So you are telling me you think PA mode works as it should?
And let me guess the radio has poor or no modulation?
Check tr11,tr12, tr13,tr14,tr15,tr16
So I guess the audio signal is not getting amplified enough, the problem is likely in the audio section. Even though PA mode works, it is not as it should be, once you have replaced the burnt transistor (or what it is) & the radio modulates correctly; you will notice a LOUD difference in how PA mode works, with almost no mic gain..
Check the tantalum caps (if this isn't a radio that you re-capped) in the audio chain.
So I guess the audio signal is not getting amplified enough, the problem is likely in the audio section. Even though PA mode works, it is not as it should be, once you have replaced the burnt transistor (or what it is) & the radio modulates correctly; you will notice a LOUD difference in how PA mode works, with almost no mic gain..
Check the tantalum caps (if this isn't a radio that you re-capped) in the audio chain.
Still though, once the audio section is kosher you may have to turn the gain all the way down and have the speaker at least ten feet away!
Tr14 and tr15 are no good. Will go and check the rest again to make sure. What's the best way to get the 13.8v to the main board right?
you say you do not have 13.8 volts to the main board. what actually is not working on the radio? do you have 13.8 volts at the power switch where you turn it on and off? you do not have 13.8 volts at all locations. some areas are 8 volts and some will be around 5 to 6 volts. do you have 13.8 volts at the VR201 I think is the right one for the main power feed to the board from the power supply.
does this radio have a plug on the back to put 13.8 volts from an external power supply? I have never seen or even worked on this radio.
according to the schematic and the owners manual the radio has a dc power plug on the back of the radio. you can use this to see if the radio works off a external power supply.
does this radio have a plug on the back to put 13.8 volts from an external power supply? I have never seen or even worked on this radio.
according to the schematic and the owners manual the radio has a dc power plug on the back of the radio. you can use this to see if the radio works off a external power supply.
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Yes not getting 13.8v at vr201 I'm getting 16.44v before vr201 ant 7.4v on the other side of vr201 when fully opened