Need advice repairing Ranger 2970N4 amp

[llilillill]

So, a little background...

I hooked a battery charger to my truck while I was at home. Later, I went out to the truck to get something and noticed my inverter was beeping with an overvoltage alarm and displaying 17 volts on the panel. After shutting the inverter off, I heard the fan running on my radio which was off at the time.

Since then, the radio will only deadkey 30 watts, max, with the variable power wide open.

I finally got around to opening the radio up to have a look last night. When you key it up on AM, one transistor heats up over 200 degrees very quickly, while the other three stay just above ambient. I'm guessing three are dead and the fourth is now way overdriven.

I don't see any blown resistors or caps. Can I just replace the transistors with a matched set and call it good? Or will something need adjustment after replacing them?

Also, the tops look to have been sanded and blacked out. From what I found on the net, they should be 2SC2879's. Anyone know for sure?

 

[Ranch55]

According to Ranger Communications, U.S.A. customer service repair folks, they specifically sent me information earlier this year telling me the transistors they used in the RCI 2970N4 are the DEI 2SC2879 transistors. I opened a couple of them up when I did a repair on a N4 radio, and they were DEI's. I installed Toshiba 2SC2879 transistors in their place.

 

[9C1Driver]

So, a little background...

I hooked a battery charger to my truck while I was at home. Later, I went out to the truck to get something and noticed my inverter was beeping with an overvoltage alarm and displaying 17 volts on the panel. After shutting the inverter off, I heard the fan running on my radio which was off at the time.

Since then, the radio will only deadkey 30 watts, max, with the variable power wide open.

I finally got around to opening the radio up to have a look last night. When you key it up on AM, one transistor heats up over 200 degrees very quickly, while the other three stay just above ambient. I'm guessing three are dead and the fourth is now way overdriven.

I don't see any blown resistors or caps. Can I just replace the transistors with a matched set and call it good? Or will something need adjustment after replacing them?

Also, the tops look to have been sanded and blacked out. From what I found on the net, they should be 2SC2879's. Anyone know for sure?

If your radio got hit with 17 volts I would think the finals are the least of your problems. If it is just the finals you will have to decide how much you want to spend. You can go to Toshibas but you don't have to.

 

[W2EKG]

The Ole Four Pounder?

 

[W2EKG]

View attachment 21641
The Ole Four Pounder?

Seriously send to Bells, Carl has experience with the PA PCB.

 

[llilillill]

If your radio got hit with 17 volts I would think the finals are the least of your problems. If it is just the finals you will have to decide how much you want to spend. You can go to Toshibas but you don't have to.

The radio still transmits and sounds alright when listening on another radio. It just doesn't have the power output it used to.

I ordered up a matched set of HG's from RF Parts. As soon as I get a minute, I'm going to put them in and see what it does.

 

[W2EKG]

 

[Robb]

So, a little background...

I hooked a battery charger to my truck while I was at home. Later, I went out to the truck to get something and noticed my inverter was beeping with an overvoltage alarm and displaying 17 volts on the panel. After shutting the inverter off, I heard the fan running on my radio which was off at the time.

Since then, the radio will only deadkey 30 watts, max, with the variable power wide open.

I finally got around to opening the radio up to have a look last night. When you key it up on AM, one transistor heats up over 200 degrees very quickly, while the other three stay just above ambient. I'm guessing three are dead and the fourth is now way overdriven.

I don't see any blown resistors or caps. Can I just replace the transistors with a matched set and call it good? Or will something need adjustment after replacing them?

Also, the tops look to have been sanded and blacked out. From what I found on the net, they should be 2SC2879's. Anyone know for sure?

This makes no sense at all. Regardless of the fact that the battery charger was on the car; the radio was 'off'. Which means there is no current flowing thru it. Pretty hard to damage something like an amp OR the radio if the power is off and it isn't keyed up.

Even if the radio was on and the voltage feeding it was 17v, it wouldn't fry the receiver portion. Would take a little more than that and would take a little while to get there.

If it is still under warranty; then send it back. Or was it modified with an amp switch to shut off power? The heating up could be due to bad solder joints or power feed to the amp board. I would test the transistors before throwing money at it. That isn't the way to fix things.

 

[llilillill]

Something caused the transistors to heat up enough while the radio was off that it caused the fan to turn on. When I saw the over voltage on the inverter, I put two and two together and concluded the battery charger was the most likely suspect.

I will check them after they are pulled out, if they test ok, then I need to look elsewhere. Here's what I do know...

1. Only one of the four finals gets hot.

2. I don't see any burned components or flakey solder joints on the board.

3. The radio used to draw about 35 amps at full tilt. Now the max is 17 amps.

It could be that the over voltage didn't have anything to do with it at all, just that it caused me to become suspicious of damage when I heard the fan running.

I won't be back home to tear into it until next Friday.

 

[Tallman]

There are amps in which the power to the finals is not run through the switch.
Most switches are rated for 20 amps maximum. The switches on the RMItaly amps cannot even begin to handle that much power. They bypass the switch and take power directly to the finals.
If you look at the KL-500 schematic the power comes in to the and is tapped before capacitors and then is routed directly to the output transformers. There is no switching for the power to the finals.
I'm not saying your is the same way, but that is a reason so many amps fail. There is an inductive kick in the electrical system when the starter is disengaged from the fields collapsing in the starter. Those voltages can be three times the battery voltage. Most have no surge protection inside.

 

[llilillill]

T

There are amps in which the power to the finals is not run through the switch.
Most switches are rated for 20 amps maximum. The switches on the RMItaly amps cannot even begin to handle that much power. They bypass the switch and take power directly to the finals.

It appears that's the way Ranger does things. The power comes in at the amp pc board with no switch. Power at the finals whenever the radio is plugged in.

The radio itself gets power from the amp's circuit board.

 

[Tallman]

Here is a more information on inductive kick.
http://www.richieburnett.co.uk/indkick.html

 

[llilillill]

And I think this just decided the question of what type of relay to use on the power feed to the radio. I was going to use a continuous duty dual battery relay like Ford used on some Econolines, and just wire it to the ignition switch. But after your post, I think I'll use a latching relay and trigger it manually after the truck is started.

I've had issues with the inverter triggering an overload error code after starting the truck.

 

[Tallman]

By Jove I think you got it! Good move on delaying the power application.

 

[llilillill]

Just had another thought...

I could wire the ignition switch to toggle the relay off if the radio is on already. This would prevent brain farts if I shut the truck off momentarily at a guard shack and then start it back up while the radio is on.