PC-122 / TRC-453 No Transmit - Help ?

[sdmahr]

I've got a Uniden PC-122 / Realistic TRC-453, (same radio) which will not transmit. Receive is still working. Red X-Mit light comes on when keyed, but on AM and USB/LSB no power output and no indication on the S-Meter.

It was working one minute, dead the next.

Suggestions on where to start? Have any of you been through this before with this chassis?

Need to understand where to begin.

Any help greatly appreciated ! !

 

[Robb]

Remove and test the final and the driver.....or did you already do that?

 

[bigwheel82]

I have a TRC-453 that has intermittant transmit problems, but on A.M only. Traced it down to the large ribbon cable that connects to the board. Best I could tell when I was "probing" around that area that the transmit came back. (I was keyed down the entire time)

 

[sdmahr]

I'm not sure what is going on with the radio. Receive works great.

I have the service manual, but that only really helps someone who knows what to do with it ! ! (this is what happens when a mechanic goes to do electrical repairs)

I went through and checked all the IC's. Below are the readings:

IC1

Pin # Voltage Should be Voltage is
1 N/A N/A
2 0.2 Floating 1-2V
3 0.1 Floating 1-2V
4 0.1 1 V
5 0 0
6 1.2 1.52
7 1.5 1.6
8 0 0
9 8 8

IC3

Pin # Voltage Should be Voltage is
1 0 0
2 3.3 3.2
3 3.2 3.2
4 0 0
5 5.8 5.75
6 7.3 7.25
7 3.7 6.46

IC4

Pin # Voltage Should be Voltage is
1 8.1 8
2 0 0
3 13.6 13.8

IC5

Pin # Voltage Should be Voltage is
1 0.1 68.5mv
2 1.9 1.95
3 1.3 1.33
4 0 0
5 0 0
6 7 7.04
7 12.7 12.83
8 13.8 13.85

IC6

Pin # Voltage Should be Voltage is
1 7.8 7.63
2 N/A N/A
3 N/A N/A
4 N/A N/A
5 0 0
6 2.8 2.8
7 4.1 4.25
8 4.1 4.24
9 7.5 7.36




Receive on the radio works great. No problem there. Just no TX. I hate to replace everything that is listed above that is off or dead as I have a hunch there is something else going on. I cannot figure out how all these are related and if just one component fault could cause all these to show like they do.

Anybody know??

 

[sdmahr]

Problem solved. Ended up being 2SA1012 transistor bolted to the back wall of the radio. Ordered a replacement and dropped a TIP42 in there till the mail-man shows up with my part.

 

[sonoma]

just saw this posting and was reading through it then saw you had found the problem. good job. the tip42 will work fine . a lot of guys are using the tip trans now since the others are so hard to find.

 

[sdmahr]

I wonder if the TIP42 has any long term disadvantages ? It seems to work great, is readily / locally available, and best of all CHEAP, not to mention it is a direct bolt/solder in fit. I tried it as a short term fix till my part gets here as I read on the net where a group of guys from the UK have been using them with good results. I can buy several TIP42's for the price of one 2SA1012 ! Wonder what happens if I just leave it in ?

 

[sonoma]

I wonder if the TIP42 has any long term disadvantages ? It seems to work great, is readily / locally available, and best of all CHEAP, not to mention it is a direct bolt/solder in fit. I tried it as a short term fix till my part gets here as I read on the net where a group of guys from the UK have been using them with good results. I can buy several TIP42's for the price of one 2SA1012 ! Wonder what happens if I just leave it in ?

I keep tip41 and tip42 and tip36 on hand to replace those parts with.a buddy of mine has a shop and he has been using them for several months now and none have went out. most seem to handle the voltages better also.

 

[sdmahr]

Well...?.if it ain't broken I'm not going to continue to fix it! I`ll leave it in there.