Yamaha RXV-2092 thermistor replacement

[matski]

Hi all,

I've got a Yamaha RX-V 2092 7 channel receiver that I know a couple of channels are out on. I want to use it as a bench test amp as it's a gutsy old thing but I have had to rob the heatsink thermistor pcb for a very similar amp that I have just sold on. I can't get the part anywhere so was wondering if anyone had any idea roughly what resistance range the thermistor uses and if inserting a fixed resistor of about 50% value would do the trick as it currently switches straight off as it is open circuit.

Thanks

Mat

 

[Nigel Goodwin]

I'm assuming the thermistor was for bias compensation?, so turning it on without it may have already killed the amp! - as both transistors will turn hard ON (which should NEVER happen).

I'm also assuming it's got a negative temperature coefficient?, so a low value would reduce the bias - shorting it out will set the bias to zero, giving class B and crossover distortion.

So I'd be inclined to try shorting it out and see if the amp still works!.

One thought! - how many of these were there?. If it was bias compensation there should be one for each channel, if there's only one it may just be an overheating sensor, turning the amp OFF if it gets too hot.

 

[matski]

Hi Nigel,

Thanks for the reply. The thermistor is purely for heatisnk temperature monitoring and control of the 24v a.c fan. Ive had two DSP-A1092 amps before and one had the same problem (the same one I've pinched this thermistor for, and which now works perfectly). I remember inserting a variable resistor across the pins and being able to adjust the fan speed by winding the resistor up but it was a while ago and I can't remember the value. It's a very simple two pin affair. I was hoping a fixed resistor would "fool" the i.c monitoring the circuit into reading a steady temperature, thereby allowing the amp to operate.

Your thoughts?

Thanks , Mat

 

[Nigel Goodwin]

I was hoping a fixed resistor would "fool" the i.c monitoring the circuit into reading a steady temperature, thereby allowing the amp to operate.

Yes it will, but it's more difficult because you haven't got the thermistor any more - if you had measured it's resistance then you would know what sort of values to be considering?.

As it is, try whatever preset you have available and see how it works.

 

[matski]

Hi all,

I have managed to get the amp to power up by fitting a 10k variable resistor across the two pins and setting it around half way. This leaves the fan on at a continuous trickle and the amp works quite happily. Back to the two output channels I originally mentioned in my post. Both outputs for Main A Right and Main B Right are blown. There is no evidence of any burn out or damage on or near the output transistors. The amp has 10 identical Toshiba 2SC5200 devices bolted to the heatsink. As I only want it as a stereo amp, what are the chances of say taking the necessary i.c's from the rear surround channels and replacing the blown ones on the main right channels? Would I need to change anything else? I'm pretty handy but when it comes to terminology and/or electronic principles some of you may have to give it the laymans touch!

Thanks

Mat

 

[SurveySez]

I know this is an old thread, but I have several of the correct thermistors for sale if anyone is interested. it's much better to use the right component rather than risk a thermal overload..