Anyone Know about RCI 2950's?

[Low_Boy]

I bought a few radios all worked including a RCI 2950 Older with yellow display. while testing it out I found it to be doing 30 AM and SSB.
and on frequency. I first lost AM. Then lost sound. It was receiving though I could tell by bars on meter. Next I lost SSB. Main 2200Uf cap C322 was shorted. I replaced it. I checked The two AM regulators and both were good. Audio chip Good and two 8V regulators. The front end of the radio is dead. It showed 28.0000 MHz then 37.000 MHz. But only after clicking the radio on and off several times.No functions worked. Sometimes a beep is heard. Tonight I turned it on and I get nothing in the front end. Funny thing I plug a speaker in PA and talk and that works when in PA mode. Did something short out and fry the front end? Not going to do anything with this now because I still have a PC122XL to finish. but if the front end is cooked it is going by by. Too bad it is a clean radio. Also I see no battery or reset button.

 

[Low_Boy]

Bad solder joint on the main board I believe.It is working perfect. Now I have to kill it again so I can find the bad joint.

 

[Captain Kilowatt]

Didn't those older ones with the orange display have a CPU battery? Perhaps it needs to be replaced.

 

[Low_Boy]

If I could decipher serial numbers I would know how old it is. I do not think it is the oldest of the old ones. Going to bed have to be up at 3:30 AM. But noticed IC4 a 5V regulator sticking up from the board is getting hot enough to melt the wax. I have to remove that and see if it is shorted. And figure out what it is doing. started to go cross eyed so more schematic looking tomorrow.
Thanks.

 

[nomadradio]

The PLL in this radio has more than one "loop" in the PLL section. Either one of two separate PLLs that are locked together can fall out of lock. The unlock detector signals are combined and feed to an audio mute circuit that kills the receiver audio, and a transmit-kill circuit like every 40-channel PLL radio.

More than one way to loose lock in either of the loops. In the early to mid-1990s radio, see that both 10.24 MHz crystals are running properly.

If either one quits, you'll see this result.

If a tweaker has diddled slugs in the PLL, that can do this, too.

Checking the hot 7805T regulator first is the smart place to start.

73

 

[Low_Boy]

Thanks nomad. My probably stupid trick of quickly going over the board with a heat gun and everything started working. I kind of think the problem lies around the IC4 area. I found many 10V caps in this radio and I can not see what is around IC4 with out removing the channel selector board. There is a cap or two that directly connect to IC4. I am still not finding IC4 on the schematics. but in one of your earlier posts I see that it controls the front end. Further more making me think it is in that area. Serial Number 735388. I really must finish one of my projects before I can start this one. Seems I usually get in to a simple fix that usually becomes a nightmare and do not want to have too many radios apart like I sometimes do.

 

[TheRealPorkchop]

I get small cubbies and put them into that, with a lid. Sounds like we might be brothers or something, I’ll have 5-6 apart at any given time. Too many projects.

My good friend Sonoma opened my eyes to the bad/cold solder joint problem. Until then, messing with a 44HP, I had no idea that was such a big issue with these Ranger chassis radios. It really is though. So maybe just touch up a bunch of joints with your iron and see if the problem goes away.

Not trying to insult you but I wasn’t aware myself, Sonoma said if you hit one and the rosin boils out under the solder, that was a bad joint. He was correct. I fixed a lot of them since and found exactly what he said. Of course I guess the correct way to fix it would be remove the solder, clean up the pad and/or part and reapply rosin and solder it back together. And then of course, clean up behind yourself with some good flux remover and a brush.

 

[PoDuck]

I see rosin bubble out from under the solder on tons of stuff. I never heard that was an indication that it was a bad solder joint.

 

[Low_Boy]

I hate when the wax from the other side comes back up through what you just unsoldered. You keep trying to suck the wax up. Extra rosin and hope it holds.

Time for bed my typing is starting to look like that cobra 29 e bay listing. I fixed it three times, hope it looks better.

 

[Captain Kilowatt]

A cold solder joint should look dull and grainy as opposed to bright and shiny. Even good bright shiny solder joints may have some flux on it or around the edges.

 

[TheRealPorkchop]

I’m just repeating what I was told and what I found to be true. It’s worth a shot to make a trip round the board with a soldering iron, don’t ya think? Might not be your problem but might help. There’s always that wonderful corrosive glue issue, I’ve never experienced it personally but Mike speaks of it a lot.

 

[kaos513]

I fixed 2 radios by cleaning the whole board first really good and used a microscope to look for bad joints method works sometimes

 

[TheRealPorkchop]

I “fixed” one by just cleaning it with flux remover, which told me there was a bad joint. So the solder iron it got.

 

[Shadetree Mechanic]

I had a radiator in a car that had a leak at one of the tank seams. I wire brushed it to see exactly where the leak was and it quit leaking.

 

[TheRealPorkchop]

So you’re saying I could peak and tune a radio with a wire brush? By hand or on a bench grinder?