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PC76XL driver and final question

1jonnyz

1jonnyz

Member
Dec 30, 2011
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I have a really nice Phillipine 76XL that had no carrier or modulation. I tested the driver, 2sc1957, that was bad. I don't have any so I figured I would throw in a 2314 driver and 1969 final. BTW, the final that was in there was a 2029. After putting these in I still had no carrier or modulation. I tested IC3 and all of the voltages and frequencies and they tested good. Everything was good at Q16. When I checked the voltages at the driver and final I would get around 20 or more volts initially and then it would come down to around 13. I tested them and the driver is shot but the final tested ok, using a BK 520B tester. My question is, do I need to change some electrolytics and other stuff in order to put in the 2314/1969 combo or is there something else wrong somewhere? Thanks in advance!!
 

After you have replaced the driver, think I would pop in a MOSFET final and change a couple of passive parts in order to make it work. Either you can get that info on the forum using the search engine or get it from CB Tricks:

http://www.cbtricks.com/miscellaneous/fet_papers/ekl/index.htm

Are you sure that the PLL circuit isn't unlocked; that too can keeep it from keying up . . .
 
I pulled the 1969 and put a 2078 in it's place. I had it working but it suddenly quit transmitting when I started to align it. I checked the voltage at TR23, the regulator, and they are good. I check the voltage on IC1 and have no voltage until I get to pin 7. I should have 4.9 at pins 1, 4, and 5. When I tried to align the PLL I got no reading on my scope when attached to R85 in RX, and I was reading 4.3 volts in RX and TX when trying to get 3.2V when connected to R88. Not sure what happened but it is getting me frustrated! Btw, I did recap the radio before I started messing with it as it had no TX when I got it. Also it has the 2314 driver in there. I do have static on receive and the PA still works.
 
there is a tuning coil in the TX section that if turned too far in one direction, will completely drop the TX power out, and make you think you blew a driver or final.

i think its L17, or L20, or L21. can't remember which.

i know because this happened to me and had me running in circles trying to find a bad part that was not there.

just key the mic and check your adjustments on these coils.
there is a chance that you will see your deadkey pop right back up after an adjustment of the right coil.

just be sure to only adjust each coil a little bit at a time because you dont want to get one so out of whack that the TX doesnt come back when the problem coil is tuned.
LC
 
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I don't think it's that LC only because I had proper voltages on IC1 and IC3, which now I don't have, I had a carrier and modulation and then after a few minutes nothing, When I checked the voltages they were not where they were before, so I think something else took a dump for some reason.
 
kinda sounds like it might be your TX mixer chip.

using a scope, or an RF probe on your DC voltmeter, trace the TX signal from the mixer chip out to the final.

you should see it grow in voltage as you go through the amplification stages.
if you come to a point where the signal goes way down in level, you have probably found your bad part.
LC

PS- make sure that when you press the mic button, that the RX/TX light goes from green to red.
if it does not, you may be out of lock and need to adjust your VCO coil.
 
Last edited:
I have a scope and I have no rf signal at all. Like I said my VCO voltage is 4.3 on channels 1 and 40, don't know if the problem is somewhere around there or not, I am still learning here. I checked the voltages on IC1 and I noticed some channels I will have the proper voltages at pins 1, 4,5, and 6, and other channels I get no voltage there?? I do get the red TX light too. The voltages on IC3 all check out fine. I do get 10.240 at pin 4 of the mixer too. Not sure where to go next.
 
That's what I use to align Cobras Robb. Channels 1 & 40 both come in at 4.3 volts. Adjusting L19 does nothing to change the voltage. For that matter, step 1 & 4 isn't working either.
 
1jonnyz said:
That's what I use to align Cobras Robb. Channels 1 & 40 both come in at 4.3 volts. Adjusting L19 does nothing to change the voltage. For that matter, step 1 & 4 isn't working either.
Click to expand...
Hmmmmm . . . I would definitely go back over that again and again until either the method is found faulty; or a part is found faulty. One or the other - for sure. Did you check the output of the voltage supply to that circuit???
 
1jonnyz said:
That's what I use to align Cobras Robb. Channels 1 & 40 both come in at 4.3 volts. Adjusting L19 does nothing to change the voltage. For that matter, step 1 & 4 isn't working either.
Click to expand...

you've just found where you should be looking!

if L19 wont adjust the VCO frequency, that is where you start.

start checking voltages on the PLL chip and the VCO chip.
LC
 
I checked the voltages on the PLL... All are ok until I get to 10,
Pin 10 should be 1.9 RX/TX Actual is .8
Pin 15 4.8/4.8 is 0
Pin 16 4.9/4.9 is 0
Pin 17 1.8/1.6 is 0
Pin 18 1.8/1.6 is 0
Pin 19 1.7/2.6 is 4.9/4.9

I have checked a lot of the caps and resistors in the area around there and found nothing out of tolerance.

All of the voltages on the VCO, IC2 were good.
I am now getting no voltage on IC3.
I am not getting the transmit light anymore, when I key up it goes out.
The voltages on the collectors of the driver and final are about 20 volts!

Also Robb, I hooked up my signal generator and could not hear anything but static, so no receive.
 
Last edited:
1jonnyz said:
I checked the voltages on the PLL... All are ok until I get to 10,
Pin 10 should be 1.9 RX/TX Actual is .8
Pin 15 4.8/4.8 0
Pin 16 4.9/4.9 0
Pin 17 1.8/1.6 0
Pin 18 1.8/1.6 0
Pin 19 1.7/2.6 4.9/4.9

I have checked a lot of the caps and resistors in the area around there and found nothing out of tolerance.

All of the voltages on the VCO, IC2 were good.
I am now getting no voltage on IC3.
I am not getting the transmit light anymore, when I key up it goes out.
The voltages on the collectors of the driver and final are about 20 volts!

Also Robb, I hooked up my signal generator and could not hear anything but static, so no receive.
Click to expand...
Then, the PLL circuit is out of lock.
Thought so!
 

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