JBL EON rare buzz/hum issue...Help please!!!

[Edzone]

It powers on and sounds but there is a very noticeable buzz/hum on the low and hi frequency driversas soon as it clicks (powers on). I has tested so many components and continuity tested for all their pc board tracks for any open track, I also has replaced the two main power supply C75/C76 (10,000uf/63Volt) caps, but nothing change., the only rare thing I noticing are the Q17 (2SB1186A) driver transistor which heats so so much., on this I have replaced this transistor by a new one and genuine together with the other side Q11 (2SD2763A) without success, so it keeps heating to much and buzz/hum. I has also replaced almost all their near associates components and the two power transistors (A1302/C3281) but nothing change. All these done on the LF Amp stage schema. Thare are anyone that has have this or something like this issue that can help me with some light/suggestions please, Thanks a million in advance!!!! (sorry because my English are not the best but I believe it can understand).

[Edzone]

Ooopss, Sorry it´s a JBL EON15-G2 model.

[Jazz P Bass]

For now, I would recommend that you do not place a load on the output.

The fact that drivers are getting hot means the repair is not finished.


Can you take a few voltage measurements around the driver transistors. (E B C)
And the bias string voltages.(Q7- Q15)

Which schematic are you working from?
As far as I know there where two versions of this amp.
Can you post the schematic that you are working from?

I have attached the power amp 'first version'.

[Edzone]

JBL EON15-G2 Vers.2.pdf

Hi dear Jazz P Bass, thanks for your response. Notice:
1) only the Q17 driver transistor is getting to hot.
2) Yes, there were two versions, I´m working on the 2nd version (number 339555) which really are the same for the two versions, the major update on the second version was the HF Amp Stage.
3) Voltage measurements:
drivers transistors Q11 E=+0.3v B=+1.0v C=+41.9v Q17 E=-0.4v B=-1.0v C=-42v
Bias St. transistors Q7 E=+83.2v B=+82.8v C=+43.4v Q18 E=-83.4v B=-82.5v C=-43.2v

I have attached the "2nd vers." schema, thanks and appreciate so much your feedback.

[Jazz P Bass]

You are going to need a scope & a signal generator to find the noise.

The static voltages look fine.

[Jazz P Bass]

Then again, maybe not.
You need to find out if it is a power supply problem, a power amp problem or a signal board problem.

First & foremost you must ascertain whether or not there is any ripple (Vac) riding on the power rails.
There are two main power supply rails on the power amp.
The 70 volt & the 36 volt. (+ & -).
And then there is the + - 15 volt rails for the ic's.(this is critical that there is zero Vac ripple).

You should be able to read offending induced ripple with a volt meter as an ac voltage where there should not be one.
Like on the output pins of the ic's.

Short of that, you may be able to disconnect the signal board & /or the eq board to see if there is a problem with any of them.