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139 XLR (858SSB) RX/TX Issue

Yup, while doing the resistance test for NPN transistors, it became apparent that both are at least partially cooked.

Should I do a mosfet conversion or Swap in the countless SC2078's leftover from mosfet conversions in Co29s? What can I use for a driver? I still have a few NTE152s
 
How about 2SC2312 for driver and 2SC2166 for the final? This thing will have a low-drive afterburner on it so I'm really not worried about lots of power.
 
They either work - or they don't. Did you test them with the diode check tests? That is most important. If you cannot get thru testing transistors correctly, you might be better off sending the radio to a shop and let them troubleshoot/fix the radio.
 
Last edited:
Robb said:
They either work - or they don't. Did you test them with the diode check tests? That is most important. If you cannot get thru testing transistors correctly, you might be off sending the radio to a shop and let them troubleshoot the radio.
Click to expand...
I did the resistance checks forward and backwards between the legs. Basically all the legs are conducting to each other without any power to the unit. The site I was reading the check procedure indicated that if the transistor failed that preliminary test, there wasn't much point in testing any further
 
The chances that both driver/final have failed are almost nil. Usually one or the other; but almost never both. So your testing method/results just concludes that a high probability that your results cannot be correct. Might want to review transistor testing if you plan on working on radios, as this is an important step to conquer.

When I test transistors with a DVM, i just used the diode test because it shows if the gate has been shorted or is still conducting one way. Apart from using a DVM, using a dedicated, cheap tester just makes the work time just go so much faster and conclusive when needing to test several. You might want to get one of those cheap testers from a US source if you are getting into this, as it helps immensely - IMO. But knowing how to use the DVM is also invaluable.

The 2166 are used as a driver and the 2312 are used as finals.

You cannot use the 2078 in a SSB radio . . .

EDIT:
Check the transistors you first replaced.
 
Last edited:
Robb said:
The chances that both driver/final have failed are almost nil. Usually one or the other; but almost never both. So your testing method/results just concludes that a high probability that your results cannot be correct. Might want to review transistor testing if you plan on working on radios, as this is an important step to conquer.

When I test transistors with a DVM, i just used the diode test because it shows if the gate has been shorted or is still conducting one way. Apart from using a DVM, using a dedicated, cheap tester just makes the work time just go so much faster and conclusive when needing to test several. You might want to get one of those cheap testers from a US source if you are getting into this, as it helps immensely - IMO. But knowing how to use the DVM is also invaluable.

The 2166 are used as a driver and the 2312 are used as finals.

You cannot use the 2078 in a SSB radio . . .

EDIT:
Check the transistors you first replaced.
Click to expand...

So use something like this guy?
 

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Umm, let's back up a step.

Should have suggested listening for the signal that feeds into the driver transistor.

If you have another radio, put it on the same channel and plug a coax jumper into it. Thread the shell of the plug at the far end of the jumper back over the plug and slide it back down the coax. Now the exposed center pin is a half-inch long "sniffing" antenna.

Key the "dead" radio and probe your sniffing antenna around the transmit-mixer section of the radio to see if you can hear a weak transmit signal from the 'dead' radio's transmit side.

If you can't, leave the driver and final alone. Doesn't mean that they are okay. But if you can't hear the signal that feeds into the driver transistor this way, your failure is UPSTREAM from the driver. No point in investigating the driver and final until you have a signal feeding into them. And that "pre-driver" signal should be strong enough to hear in your test receiver. Might have to get your sniffing antenna really close to the transmit-mixer circuit, but you should be able to hear it on the test receiver.

And if you have a 'scope, you don't need to use this trick.

73
 
nomadradio said:
Umm, let's back up a step.

Should have suggested listening for the signal that feeds into the driver transistor.

If you have another radio, put it on the same channel and plug a coax jumper into it. Thread the shell of the plug at the far end of the jumper back over the plug and slide it back down the coax. Now the exposed center pin is a half-inch long "sniffing" antenna.

Key the "dead" radio and probe your sniffing antenna around the transmit-mixer section of the radio to see if you can hear a weak transmit signal from the 'dead' radio's transmit side.

If you can't, leave the driver and final alone. Doesn't mean that they are okay. But if you can't hear the signal that feeds into the driver transistor this way, your failure is UPSTREAM from the driver. No point in investigating the driver and final until you have a signal feeding into them. And that "pre-driver" signal should be strong enough to hear in your test receiver. Might have to get your sniffing antenna really close to the transmit-mixer circuit, but you should be able to hear it on the test receiver.

And if you have a 'scope, you don't need to use this trick.

73
Click to expand...

Turned on my AR1000XLT to 27.215, put the cobra on 21AM, and clicked the key on/off while dragging the antenna around the entire board. Nothing there.....

EDIT: Still trying to figure out what I possibly could have done to an otherwise working radio during a recap. C94 was the only one installed incorrectly, I checked every other one vs the PCB markings this morning.
 
Are we sure that it's receiving on the channel that's selected? If the PLL is not locked, you can still hear noise and maybe channel chatter.

But if the PLL is not locked, this will totally shut down all transmit signals at the transmit-mixer stage.

Pin 1 of the uPD858 PLL chip is the lock detector. Should read zero Volts.

73
 
nomadradio said:
Are we sure that it's receiving on the channel that's selected? If the PLL is not locked, you can still hear noise and maybe channel chatter.

But if the PLL is not locked, this will totally shut down all transmit signals at the transmit-mixer stage.

Pin 1 of the uPD858 PLL chip is the lock detector. Should read zero Volts.

73
Click to expand...

This is probably a really dumb question but I'm still learning so forgive me.

Do the Driver and Final need to be installed to receive? both are currently unsoldered and sitting on the bench next to the radio.
 
They should not have any influence on the receiver in this radio. The relay totally disconnects the transmitter side from the antenna while receiving.

Other radios that don't have a relay can behave differently.

73
 
nomadradio said:
They should not have any influence on the receiver in this radio. The relay totally disconnects the transmitter side from the antenna while receiving.

Other radios that don't have a relay can behave differently.

73
Click to expand...

Just hooked up a 29 LTD WX to a mag mount antenna stuck to a file cabinet. Zero receive on the 139. I'll try to find a pinout diagram for the 858 and check that lock pin.
 

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