CurtPalme.com Home Theater Forum

[Jeremy112]

Okay mac, this one is a bit different.

It's an STR-DH100, had a blown amplifier channel and I repaired that, got it to come out of protection. And audio is heard.

Problem is, the volume can be barely turned up (say level 20 out of 70) and if I leave it sit, the amplifier gets the heatsink so hot It could probably fry the outputs and throw the unit back into protection.

Another issue with it, and its probably related, is if I raise the volume up to about 40-50 it throws the unit into protection as well. Before it goes into protection, volume is still not very loud out of the speakers at that level, which it should be.

[Jeremy112]

Also, if we fix this one, we fix the last STR-DH100 I have as well, it has the same exact issue. Only that one had no blown channels.

[macgyver655]

Check for DC on the speaker outputs.

[Jeremy112]

only 1 or 2 millivolts on the speaker outputs, but I noticed it doesn't matter if the volume is up or not, the amp just gets HOT, and I noticed when I turned the unit off and on I could hear the hum of the transformer, something I usually don't notice.

[Jeremy112]

Would substituted outputs be the cause mac? I use some that weren't direct subs, but they were "good enough" to make it work...

I could put some originals in there once they get here if you think it would make a difference.

[RayN999]

Only thing that came to my mind on this was that the bias current on the transistors was too high, but Jeremy says there's no adjustments for the bias current. So I'm stumped.

Ray

[macgyver655]

What were the substitutes you used?

What were all the parts you replaced? Give me location ids.

[Jeremy112]

I replaced both the emitter resistors with originals (from a receiver that used the same ones and had a smashed faceplate)

I used 2SA1102, and 2SC2577 I replaced all 4 outputs and both emitter resistors. Everything else checked out.

[macgyver655]

I'm curious how you came up with that cross.

[Jeremy112]

To be honest, I just compared the specs of the originals vs the subs, they seemed close, but really the subs are designed for a much older receiver

I threw them in anyway because I figured what the hell, and if it fried I wouldn't have lost sleep over it

[macgyver655]

What I can't tell you is if putting in the correct ones will solve your problem as there may be others damaged parts.

What I can tell you is I would never of considered those parts for replacement.

If you decide to get the correct ones and continue, let me know.

Did you test the parts you removed to see if they were bad?

[Jeremy112]

I did test the removed parts and yes they were bad, both channels had shorted outputs. I'll order a set of the correct ones and we'll resume the repair on it once I get them.

I have a Pioneer VSX-50 that overheats we can tackle in the meantime if you'd like.

[macgyver655]

Not a problem. Give me more details on the 50.

[Curt Palme]

Generally speaking, I haven't had a poor spec transistor cause overheating. I'd suspect a leaky driver transistor, shorted bias diode or transistor, etc.

Whenever I get in an amp with blown outputs, I always pull out all transistors going 'back' towards the preamp section. Once I get a full section (driver/bias/predrivers) that aren't blown,l then I assume that the circuits further back aren't damaged. It's amazing how many transistors leak slightly after the outputs are blown, causing havoc in the circuit.

Also generally speaking, distortion in an amp without anything smoking/overheating/getting hot means that you have an open circuit somewhere, and smoke/overheating with or without distortion is due to something shorted or leaking.

I finally nailed a convergence board fault that was driving me nuts over years. On powerup, one of the output transistors would short instantly. Turns out one predriver transistor had a high resistance leak on it. I made the mistake of measuring it incircuit, which didn't show the leak. Once I stopped cutting corners and pulled the transistor, I saw the leakage. Now to try that on the other 5 or so boards I have stored here over the years... A convergence amp is nothing more than an audio amplifier by design...

[Curt Palme]

Generally speaking, I haven't had a poor spec transistor cause overheating. I'd suspect a leaky driver transistor, shorted bias diode or transistor, etc.

Whenever I get in an amp with blown outputs, I always pull out all transistors going 'back' towards the preamp section. Once I get a full section (driver/bias/predrivers) that aren't blown,l then I assume that the circuits further back aren't damaged. It's amazing how many transistors leak slightly after the outputs are blown, causing havoc in the circuit.

Also generally speaking, distortion in an amp without anything smoking/overheating/getting hot means that you have an open circuit somewhere, and smoke/overheating with or without distortion is due to something shorted or leaking.

I finally nailed a convergence board fault that was driving me nuts over years. On powerup, one of the output transistors would short instantly. Turns out one predriver transistor had a high resistance leak on it. I made the mistake of measuring it incircuit, which didn't show the leak. Once I stopped cutting corners and pulled the transistor, I saw the leakage. Now to try that on the other 5 or so boards I have stored here over the years... A convergence amp is nothing more than an audio amplifier by design...

[macgyver655]