Teaberry Stalker Two No AM output

[majorxlr8n]

Greetings,
Have a 40 ch Teaberry Stalker Two base that has barely any am power output - test meter barely moves. Receives perfectly on am/ssb. Transmits fine on ssb (15 watts) so mic works fine. radio is dead on frequency on ssb but dont have enough carrier to test am. I have already replaced 4 caps (3 470uf and 1 1000uf) which restored receive and ssb transmit power. should I continue recapping or do I need to look elsewhere for this issue? much thanks!
Marty

[tramd]

You may want to replace all the electroytics. They were only meant to last 10-15 years so by now they are long past due for replacement. Don't bother with any tantalums though as they rarely go bad. Depending on the model it could also be the AM regulator transistor. If you have a schematic it may show what the voltages should be. CBtricks may have a manual and schematics depending on the model. A SAMS book schematic will show all the voltages for all the circuits so it makes it easy to determine if you have all of them present plus it will show all the voltages at every transistor which will help to troubleshoot it plus have the alignment procedure. If it has a board like many of the other radios of that time such as the PC-385 board that has the 8719PLL then you can use info from searches on forums for that board or radios with that board to help you find the problem also.

[majorxlr8n]

Tramd, thanks for the reply!

the board on this is a PC189-AB. The same as a Midland 79-893. There appears to be little info on this particular board. I'd love to find a Sam's book for this. I've been shooting blind as the factory schematic lists no values for many of the components. I've tried checking am/ssb detection control diodes D7, D8 & D9. 7&8 test ok. D9 showed dead short in circuit but seems ok when removed. I'm going to replace it once I get a replacement..

[tramd]

That's common with some diodes when in circuit. Depends on the circuit and what the diode is being used for. Sometimes turning a switch on or off will change how it tests in circuit when they seem to be a short or open. If they test okay out of circuit they are okay. I don't see a specific listing for it in the Sams. It says it's the same as a Cobra 139XLR but they use the PC-196BD board which may be close enough. But if it is like the Midland 79-893 I would use that SAMs book which is CB-211. The only difference would be that the Midland had no internal power supply as it's a mobile.

[majorxlr8n]

I'm taking your advice on the am regulator. Found two 2SD325's mounted on the metal side support but I'm not sure which is the correct one. One is hard soldered, the other one actually has a plug in connector

[tramd]

Not sure what the insides look like but on the PC-196BD boards the regulator is not far from the driver and final and is mounted to the same heat sink. I would guess that is how yours is. There will be a another transistor a 2SC945 (the regulator controller) right by it on the board. Voltages for the 2SD325 will be about 13.7VDC on the collector, 6.2VDC on the base and 6.8VDC on the emitter. For the 2SC945 it will be 6.2VDC on the collector, 4.3VDC on the base and 3.7VDC on the emitter.

[majorxlr8n]

ok I replaced the plug in regulator and actually got 20w ssb but still no am xmit output. I replaced the 2nd one but it appeared the trace peeled away, so I soldered a jumper in its place. Now I have ZERO am and ZERO ssb watts output. I really messed this up now. Got a Sams #211 yesterday but I have to take some time to digest this all. The new transistor could be bad or I messed up the solder locations...

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Not sure what the insides look like but on the PC-196BD boards the regulator is not far from the driver and final and is mounted to the same heat sink. I would guess that is how yours is. There will be a another transistor a 2SC945 (the regulator controller) right by it on the board. Voltages for the 2SD325 will be about 13.7VDC on the collector, 6.2VDC on the base and 6.8VDC on the emitter. For the 2SC945 it will be 6.2VDC on the collector, 4.3VDC on the base and 3.7VDC on the emitter.

Thanks for this!

I repaired another bad trace. Used the Sams to verify and now the am regulator makes proper connections, verified with ohm meter.

installed 2 new 2SC325's.

tested at final, I got 6.57 volts on base & emitter, 13.71 on collector.

Now I'm lost...

[Gold Diamond]

You mentioned that you achieved 20 watts SSB output". Is your radio a CB or some other service? I believe CB SSB has a limit of 12 W peak to peak in the U.S.

[majorxlr8n]

You mentioned that you achieved 20 watts SSB output". Is your radio a CB or some other service? I believe CB SSB has a limit of 12 W peak to peak in the U.S.

its a 1976, first generation 40 channel cb radio with am/ssb. its not uncommon to see the ALC turned up to achieve about 20 watts ssb output - however, I did not touch the ALC.

[Gold Diamond]

Learned something new. Thanks.

[tramd]

majorxlr8n have you checked the regulator control transistor 2SC945 next to the AM regulator? You should have according to the Midland 79-893 schematic 5.09vdc on the emitter, 5.74vdc on the base and 7.5vdc on the collector. That collector voltage should be the same as the base voltage of the 2SD325 AM regulator. The voltages may not be exactly as the ones I listed but should be close. Actually on a 458/457 schematic they are 3.69 on the emitter, 4.33 on the base and 6.23 on the collector. Also have you tried adjusting the AM TX power level which should be right next to these transistors?

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If you have correct voltages at those points then the the output from that circuit goes through the transformer and then to the CB/PA switch. That may be dirty or defective. Then it goes to the mode switch. If you measure the voltage of the collectors of the driver and final transistors there should be around 5vdc in AM mode and 13.7 in SSB. That will be a quick way to see if the CB/PA switch and mode switch are working.

[majorxlr8n]

majorxlr8n have you checked the regulator control transistor 2SC945 next to the AM regulator? You should have according to the Midland 79-893 schematic 5.09vdc on the emitter, 5.74vdc on the base and 7.5vdc on the collector. That collector voltage should be the same as the base voltage of the 2SD325 AM regulator. The voltages may not be exactly as the ones I listed but should be close. Actually on a 458/457 schematic they are 3.69 on the emitter, 4.33 on the base and 6.23 on the collector. Also have you tried adjusting the AM TX power level which should be right next to these transistors?

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Added 12 minutes 58 seconds after previous.
If you have correct voltages at those points then the the output from that circuit goes through the transformer and then to the CB/PA switch. That may be dirty or defective. Then it goes to the mode switch. If you measure the voltage of the collectors of the driver and final transistors there should be around 5vdc in AM mode and 13.7 in SSB. That will be a quick way to see if the CB/PA switch and mode switch are working.

I MUST THANK YOU for taking the time not only to reply, but for perusing the schematic for me. That takes time and a trained eye. I greatly appreciate that! I haven't dug back into it for a week. Kind of spent too much thinking, tracing the schematic etc and needed a break. I'll heed your advice on checking the 2SC945 - I think its right ahead of the 2SC325 on the circuit board IIRC but should be easy to locate. I've played with the mode & cb/pa switches some but you hit another good point there to check.

Again, MUCH THANKS for your time & input. I'll get cracking on this!
Marty

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Added 1 month 17 days 23 hours 49 minutes 48 seconds after previous.
Had family issues keeping me from this but spent a good 2 hours on it this am...

the final xmit voltages are below what they should be, and the voltages FALL after a few seconds.

I back traced (via Sams) and those transistors also are low voltages with falling values.

DUMB QUESTION: since the final voltages are too low, should I be testing AHEAD or BEHIND them?

Very wet behind the ears with testing here but have the will and brain to learn.

THANK YOU!

[tramd]

Since you have the SAMS it should show all the voltages coming off the power supply and going out to all the different circuits in the radio. I would start with the voltage at the power supply and make sure it is correct. Should be around 13.8vdc or so. The book will tell you what it should be set to. Then check all the voltages it shows for AM transmit at the various points.This will help you break it down to a specific circuit. SAMS usually has pics of the bottom sides of the circuit boards that show where to measure the voltages at.

[majorxlr8n]

TramD: thank you again for the reply. I did check the power supply voltage, it was 13.86 which is good. I did poke around some an hour ago and had SSB working once again, but it only lasted maybe a minute - so its no am and ssb output.

I'll take your advise and start checking from the power supply feed to am/ssb xmit...

Marty