Johnson 430 problem with TX no collector voltage.

[vswr]

I have this radio and Im pulling out my hair with it. I only have the sams for it and I m having the wierdest problem with voltage getting to the driver and final. These voltages all appear correct. The transmitter gets its voltage from #1. The next part shows #1 feeding a diode going up throgh the transformer and making to #48. Well, there appears to be 2 number 48s but only 1 on the board. Both rf transformers both 1k resistors and both transistors test good. Matter of fact, it worked for a micro second at some point during my testing but died as soon as I gave it audio. I even tried ohms checks and got infinity on the resistors side connected to 48 and of course no DC. If there is any sort of jumper, I dont see it. Might have to redraw this section. Any ideas?

 

[brandon7861]

They both show 48 because if you follow the wire around the right side of that picture, they are both connected. You could have 100 points that say 48 and they would all be the same trace.

Maybe the audio transformer's secondary went bad. If 13v goes in and nothing comes out the other end of the winding...

 

[vswr]

I appreciate the info. I am fully aware how the sams spread out connections to indicate points of contact. At the top 1, 50 and 48, i get the correct voltage. That rules out transformer winding issues right there. Thanks though. Appreciate the help.

73s

 

[TM86]

I'm probably wrong, but this is screaming broken trace or cold solder joint at me. If the only physical connection between the two 48's is circuit trace then I don't see how it could be anything else from the symptoms described.

If this is one of the early double sided boards you might try reflowing the connections on everything that is on the path between the two 48's. Or maybe even just removing the solder from those components and going new with some flux just to make sure all the joints are clean.

Only other thing would be if the original electrolytics are still in there is maybe check for signs of leakage as electrolyte will corrode traces to the point that they become disconnected. If that happens where there's a component on top of the trace you'll never see it.

 

[brandon7861]

What looks like a trace on the schematic may have been a wire, and that wire may have been messed with. Perhaps someone cut it at some point to insert a current meter and did a bad job reconnecting it. Can you post pictures?

 

[vswr]

I'm probably wrong, but this is screaming broken trace or cold solder joint at me. If the only physical connection between the two 48's is circuit trace then I don't see how it could be anything else from the symptoms described.

If this is one of the early double sided boards you might try reflowing the connections on everything that is on the path between the two 48's. Or maybe even just removing the solder from those components and going new with some flux just to make sure all the joints are clean.

Only other thing would be if the original electrolytics are still in there is maybe check for signs of leakage as electrolyte will corrode traces to the point that they become disconnected. If that happens where there's a component on top of the trace you'll never see it.

It could very well be. I did reflow what looked like bad solder on the bottom of the board. This was fixed before I got it. Some runs were repaired. Some bad solder joints could be or runs on the top side for sure. Im gonna flux the area and reflow all that has to do with 48 to each collector. I did change the electrolytics in that area.

 

[vswr]

What looks like a trace on the schematic may have been a wire, and that wire may have been messed with. Perhaps someone cut it at some point to insert a current meter and did a bad job reconnecting it. Can you post pictures?

Pics won't be easy to do. The Sams is actually a better illustration than any pic I can provide. Im gonna look for issues above the board.

 

[vswr]

UPDATE: Turns out that it was a resistor that had good continuity on onecsidenofcthe board, and no continuity on the other side of the board. A good reflow solved the problem. Thanks for the support guys!