QUAD 606. Shifting power supply voltage on right channel.

  • No one logged in.

10-Nov-2019 08:14 PM

Not Available

Posts: 13

Hi,

Another QUAD power amplifier with shifting DC voltages.

My first amp having this issue was a 306 and now it concerns a non-modified QUAD 606; one of the very first series.

Its DC voltages of the right channel start to shift to the negative side after 2 seconds.

The voltage over R36 is getting smaller and the one over R37 bigger.

There is hum audible on the right channel.

If I found the cause I will update this topic.

Cheers,

Harry

  Reply

11-Nov-2019 04:21 AM

EJP

EJP

Posts: 1676

I would wonder about C9 and also T15/16. Measure all four resistors too.

Keep us up to date on this. I am fighting a similar issue on a 520.

EJP

  Reply

11-Nov-2019 10:13 AM

Not Available

Posts: 13

In an earlier post about a 306, resistor R3 looked fine but measured infinite instead of 3.3kOhm. 

Harry

  Reply

16-Nov-2019 02:48 PM

Not Available

Posts: 13

Hi,

Main cause. R37 (9.1kOhm) was infinite.

Further replacements (on both channels):

R41 and R3 now the correct values (in the production these were swapped on both boards);

R37: 9.1kOhm;

T15: into ZTX653 DIODE INC. NPN;

T16: into ZTX753 DIODE INC. PNP;

IC1: TLC271CP;

C3: BFC236825684, 680nF 100V;

C16: D47K33 Y5P H63L2R;

Fresh layers of thermal paste on both heatsinks of each channel.

  Reply

16-Nov-2019 03:54 PM

Not Available

Posts: 13

Additional info regarding the PCB version: M12910 - Issue 1.

After having repaired the 606 by replacing the listed parts I found that the idle hum has reduced a little bit more.

@EJP. I hope you will fix your 520 amp.

Cheers,

Harry

  Reply