Charming Samson Servo 200 Fried output transistor pair

[nylicens]

I've got this Samson Servo 200 amplifier that has fried one channel's output transistors. I am ordering in new TIP35/36's to replace and also some other driver transistors, but I thought I'd ask here if anyone has had experience with Samson Servo 200/300/600 series amps. If you have had the experience of replacing the output transistors, what other transistors did it take out when the it blew?

[Enzo]

AMps are amp, they mostly all work the same way.When the outputs blow up, we replace them, but we also always check all the resistors associated with them for open condition. Then the drivers and predrivers should be checked along with their resistors,

[nylicens]

More...

AMps are amp, they mostly all work the same way.When the outputs blow up, we replace them, but we also always check all the resistors associated with them for open condition. Then the drivers and predrivers should be checked along with their resistors,

I guess what I meant to ask was if these specific units have a habit of blowing out the outputs. I have read other places where these particular units are available used but many are blown, so I wanted to get an idea of whether or not I might better spend my time on other things.

[J M Fahey]

Not "a habit" .

Any amplifier can blow, usually by shorting output transistors, which as Enzo said almost always take out other components with them.

In any and all cases, you must troubleshoot, meaning you must measure voltages, shorts, some parts values, replace them (not any and all at random) , turn amp on afterwards but for safety reasons in a power limited way, with a Variac or a Limiting Bulb and remeasure again.

When you think it looks good, you connect a speaker and test it works properly putting out a couple Watts and only then, you connect it straight to the wall socket.

All amps, no matter brand or model are repaired in a similar way.

This is as generic an explanation as can be.

Applying a cure "seen in a Forum", or something which worked for others in general does not apply, each amp has its own problems, and you must check anyway.

Is it worth for you?
Yes if you have reasonable skills or time and patience and follow suggestions.

If not, it can be frustrating.

[nylicens]

Yes if you have reasonable skills or time and patience and follow suggestions.

If not, it can be frustrating.

I know. I've been repairing electronic gear since 1966.

I failed to make clear I was asking about the problems with this *specific* piece of gear as I had heard that they are pretty regularly blown. I wanted to see if there was any info as to why.

[Enzo]

These amps are not unlike other Samson models. As to why they would fail, I would first suspect the users overtaxing them. I know of nothing inherently frail in them.

ABout the only shortcut for Samson I can think of is the small electrolytic caps dry out sometimes, in the speaker relay control circuit. But you don't have that symptom.

[km6xz]

The Servo series of amps are reliable low to moderate duty cycle amps that are built to be light weight(before Class D came out). My shop was a warranty station for them and never saw a rash of failures just the typical problems of too low of Z load or a burned VC with low but not low enough of a load z to trip the relay. Don't run them without good air circulation on "11" all night in an outdoor gig and they will be fine.
When a unit seem to have a lot of them available in unrepaired condition you have to consider how many there are in circulation and whether they cost enough to motivate people to have them repair. Almost all analog gear is rendered beyond economic repair solely because of incompetent techs either could not figure the circuit out or had butchered it so badly that a competent tech does not want to touch it. As Enzo wrote, amps are amps, no mystery or magic that requires the secret handshake or saying incantations over them. Lets put it another way, I would rather repair a Servo Samson than say a Mesa amp solely because the guys who laid out the boards in Korea, knew that someone eventually would need to get access to both sides of the boards. Im moderate use the Samson should last many decades. That can't be said of any modern digital gear since when the parts go out of production, that is it. There are digital circuits less than 10 years old where there are no second sources of parts in existence, like masked programmed mpu's or gate arrays.

[nylicens]

Replaced tips and drivers - sad

The Servo series of amps are reliable low to moderate duty cycle amps that are built to be light weight(before Class D came out). My shop was a warranty station for them and never saw a rash of failures just the typical problems of too low of Z load or a burned VC with low but not low enough of a load z to trip the relay. Don't run them without good air circulation on "11" all night in an outdoor gig and they will be fine....

Thanks for the info. Since these units are pretty cheap I wanted to see if fixing was worth it. I replaced right channel's Tip35/36 and 1837/4793 and checked the rest of the xistors as best I could. Replaced fuse and fired up. Heavy distortion on the the left and nada on the right, no leds light on power pcb. Already have 3 hours into this so I just may bin it.

[plec.22]

Thanks for the info. Since these units are pretty cheap I wanted to see if fixing was worth it. I replaced right channel's Tip35/36 and 1837/4793 and checked the rest of the xistors as best I could. Replaced fuse and fired up. Heavy distortion on the the left and nada on the right, no leds light on power pcb. Already have 3 hours into this so I just may bin it.

One way to solve amplifier fault such as this one, is not to pop replacement parts in and power up but to use it's work channel to check input circuits followed driver and out put circuit..even check current draw with no signal/no loads. time spent going over things is worth it to ensure you don't miss anything.

Some of us have spent many hrs going over pain in the butt fault's and do the work shop jig when it works..