Eros phono peamp no o/p left ch.M

[cyrius]

My Eros worked perfectly for the past 4 months,then suddenly the left channel went out.No output on the left.The leds on the regulator board light up as well as the ones on the right preamp board.But all the leds on the left do not light up.The voltage on the IA left board is only 22v.A resistance check on the IA line shows no overloading whatsoever.All semiconductors on the preamp board show no defect.Can anyone help what should i do next?

[Paul Birkeland]

Pull the 6922 and EF86s.

Measure the voltages on the high voltage shunt regulator board (the one above the 12BH7) with the 12BH7 installed.  There are testing procedures for this in the manual.

-PB

[cyrius]

I finally had time to take the measurements.
Voltage on D1 (A side) is 295 v
Voltage on D1 (B side) is 295 v
Voltage on K of the TL 431 (B side) is 8v
Voltage on K of the TL 431 (A side) is 10.6v
I also noticed that the 2 LEDs of the A side light up full when switched on whereas the B side ones take a few secs.
I suspect the 12BH7.....Waiting for your advice.
Thanks

[Paul Birkeland]

What do you get at +Reg on each side of the PC board above the 12BH7?
(There is not currently any evidence that your 12BH7 is to blame for anything)

[cyrius]

Hi D.B
Readings are as  follows:
+ Reg on B side.....219.7v
+ Reg on A side.....222.9v
Cyrius

[Paul Birkeland]

OK, the high voltage regulator (and 12BH7) are operating perfectly.

+Reg on each side feeds IA and IB on each side.

You reported 22V at IA on the side that wasn't working, so it's possible that you have a broken wire or a solder joint that isn't permitting this connection.

[cyrius]

Right.....i will check the wire connection/solder and report tomorrow morning.
cyrius.

[cyrius]

Hi Paul,
Good news,the left channel is now working.
After taking several measurements of the regulated supply of the left channel,i noticed that it is intermittent sometimes 225v and sometimes 22v.I removed the regulator board and resoldered the 2N2907 which i noticed had corroded legs.I also replaced the TL431 just in case.When firing up all voltages returned back to normal!
Was it bad contacts on the 2N2907 or a faulty TL 431 the culprit ?
Thank you for your help!
Best regards
Cyril

[Paul Birkeland]

Probably a bad solder joint on the 2N2907.  If the 431 gets disconnected, the regulated voltage will pop up to about what is coming out of the power supply board above the power transformer.