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Old style connex 3300 no modulation?

Low_Boy

Low_Boy

Sr. Member
Jan 21, 2010
1,934
1,199
173
Rochester N.Y.
I have a old connex 3300 that has no modulation. But if you remove TR53 or R249 modulation comes back. Works with echo on or off when either component is removed. Audio chip is also good. I have been poking and testing and can not find anything wrong or unhooked. Also TR53 tested good and R249 10 K ohm resistor is good.
Anyone ever see this before?
 

If you move a component around and then the radio works; then what does that tell you?

First best guess would be a poor solder joint. Besides old caps in old radios, bad solder joints are the next biggest trouble area. That is a little time consuming to remedy, but it gets the job done. You also need the right gear and technique to do it correctly. Small chisel point soldering tip on a 20-30 watt iron, solder sucker, solder wick, flux, rubbing alcohol and small brush to clean off flux residue, and adequate ventilation. By the time you remove/replace solder on 30 joints, you should be an old hand at it.
 
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Robb, I think this is the IRF520 driving two that I had so much trouble with.
Short version : D76 and IC4 the NMJ4558D not playing nice.
Repair: D76, TR36, TR37, C199. (IC4 survived)
What a merry chase. I don't know which solved which as I have to admit to a shotgun repair :-/
I'm a hack after all :wink:
 
Robb said:
If you move a component around and then the radio works; then what does that tell you?

First best guess would be a poor solder joint. Besides old caps in old radios, bad solder joints are the next biggest trouble area. That is a little time consuming to remedy, but it gets the job done. You also need the right gear and technique to do it correctly. Small chisel point soldering tip on a 20-30 watt iron, solder sucker, solder wick, flux, rubbing alcohol and small brush to clean off flux residue, and adequate ventilation. By the time you remove/replace solder on 30 joints, you should be an old hand at it.
Click to expand...
Ok so not just reflow the solder but replace it? Taking notes.
 
Robb... I looked back at my post and I never said the radio worked after moving any components. So obviously I have fixed a few radios in my time and I am not stupid like you are trying to make me out to be.

Possibly I am interpreating Your first paragraph as a bit contrary and if I am, I am sorry. I do appreaciate your help but obviously can not take the time or the space to write every detail that I do while tryingto get a radio going. But the easy first step kind of thing like brushing and poking the board while looking for bad solder connections is a step I thought I did not think had to be mentioned.

Now I did say how I got the radio to work by removing one or another component at a time.

So again I will try not to take any offense at that paragraph and if I misunderstood it. Sorry.
 
Kopcicle
Thank You. This radio is factory no IRF520 in this one.
I started probing IC4 with my scope With R249 in and out of circuit and Found With R249 out I get modulation on pin 1 and 3. With R249 in I only show modulation on pin 1.
Then I had to stop to take a sick friend to the hospital and will resume this after work tomorrow. I will start by checking the components you mentioned.
Thank You,
 
Low_Boy said:
Robb... I looked back at my post and I never said the radio worked after moving any components. So obviously I have fixed a few radios in my time and I am not stupid like you are trying to make me out to be.

Possibly I am interpreating Your first paragraph as a bit contrary and if I am, I am sorry. I do appreaciate your help but obviously can not take the time or the space to write every detail that I do while tryingto get a radio going. But the easy first step kind of thing like brushing and poking the board while looking for bad solder connections is a step I thought I did not think had to be mentioned.

Now I did say how I got the radio to work by removing one or another component at a time.

So again I will try not to take any offense at that paragraph and if I misunderstood it. Sorry.
Click to expand...
No, I don't think you are stupid and that isn't why I elaborated..
It was my fault for not reading your post carefully; my mistake. When I do elaborate about something, it is for the benefit for any new readers so they can grasp a point.

Back to business; does this radio have the RWOB mod done to it?
 
Thanks Robb.
No Red wire on bottom mod. and No NPC. I had this radio in my truck for a while it never put out much more than 20W even on high with the NPC mod. It had been sitting. I started looking at it and demodded it. Changed all 10V caps Found a burnt resistor R252 but still checked good replaced that. Power was about the same. Possibly a bit more. Cut R249 to see if there was a increase. There was not a lot of difference so touched it back to see what it looked like on the scope and lost modulation. Took R249 out and it worked. Removed tr53 checked that it was good radio worked with TR53 out. Put it back plenty of carrier no modulation.
I am done for tonight. Typing is getting bad so that means shower and off to bed.
 
I had replaced TR51 probably about a year or so ago. So I checked the voltage and the collector was reading about 2 volts low on key up. I poked arount there a bit. Everything looked good so I desoldered and soldered everything back up. Collector voltage came up and the radio is working again. Still a bit low on power low 4W RMS and about 12 PEP. High 8 RMS and about 26 PEP. It may have a week final, Driver or Pre Driver.

Robb thanks for suggesting TR51. I am not sure I would have looked there.
 
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Low_Boy said:
I had replaced TR51 probably about a year or so ago. So I checked the voltage and the collector was reading about 2 volts low on key up. I poked arount there a bit. Everything looked good so I desoldered and soldered everything back up. Collector voltage came up and the radio is working again. Still a bit low on power low 4W RMS and about 12 PEP. High 8 RMS and about 26 PEP. It may have a week final, Driver or Pre Driver.

Robb thanks for suggesting TR51. I am not sure I would have looked there.
Click to expand...
Congrats on finding the bad part; always makes me grateful to find them straight away. I'm also more grateful for finding a well hidden problem too!

Again, I am going to be as thorough as I can , so take it all in stride if you know this stuff . . .

As any radio ages and especially if they get bumped around a lot in a mobile situation, the TX coil chain can and will go out of balance. This is also due to the fact that as a radio gets older, the values of some components will change and season. Not always a good thing. Bumpy rides will also just throw the coil cores out of whack; it will also throw board VR's out too.

Sooo, it may be best to re-peak the TX coils and see if that doesn't put it back on top using a dummy load (essential) and a 1khz audio source for the mic. If you know how to do this, then that is what I'd do and then judge the results and the situation. Doubt very much that a final or driver is going foul; but not entirely out of the realm of possibility either. Just more unlikely.
 
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