Looking for some schematics for this amp. Has issue with the rear channels. draws excessive current. The power supply fets (IRFZ34) get hot and one bank of the BTJs (2N6487)gets hot. But i cant find the reason. Nothing seems to be out of order. I have removed each transistor and checked for defects and reinstalled. Real head scratcher here. Thank you in advance.
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The biasing may have drifted on the channel that's getting hot if all of the outputs in that channel are heating (roughly) evenly.
Measure the voltage across all of the emitter resistors in that channel and compare the readings to the voltage across the emitter resistors in the other channels.
Measure the voltage across all of the emitter resistors in that channel and compare the readings to the voltage across the emitter resistors in the other channels.
You measure the DC voltage directly across each emitter resistor.
Since there is no bias pot, biasing is likely done via transistors and thermistors. One or more may be defective. There may be a way to replace fixed resistors with the bias pots (see locations for what may be bias pots).
How much does heating/cooling the thermistors between make the idle current change?
Since there is no bias pot, biasing is likely done via transistors and thermistors. One or more may be defective. There may be a way to replace fixed resistors with the bias pots (see locations for what may be bias pots).
How much does heating/cooling the thermistors between make the idle current change?
I measured the thermisters at room temp. all were the same. in circuit were 2.7k ohm. I applied power and heat to the closest one to the bank and o change to the over current. The thermister did go down in value though. It draws over 10 amps at idle with no speakers attached. Attached is the area of issue.
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i put a 10 ohm resistor across the thermister and the voltage came down to 1.8v. But the amp still draws 10+ amps. i have a current regulated power supply for testing. max current is 10 amps. I also pulled C6, C26, Q64 and replaced the 4 output transistors with new ones. The caps all checked good and Q64 checked good as well. Nothing has changed.
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