Yamaha Q2031A 31-band Graphic Equaliser

[Nevillet]

Hi All,

I'm after some help with a 25 year old Q2031A GEQ with gives no output.

When powered on each peak LEDs lights on both channels and there is no output.

All the LED's light when the appropriate button is depressed.

When the EQ button is depressed on each channel relay (RLY1&2) is engaged/disengaged.

When the unit is powered on/off relay 3 engages/disengages.

I have attached the service manual.

Many thanks

https://www.badcaps.net/forum/attach...1&d=1625678093

[R_J]

Re: Yamaha Q2031A 31-band Graphic Equaliser

Do the peak leds go out if you remove the input signal? or are they always on?

[Nevillet]

Re: Yamaha Q2031A 31-band Graphic Equaliser

The peak LED's are lit regardless of I/P. So If no signal is connected to the inputs the peak LEDs still light up.

[R_J]

Re: Yamaha Q2031A 31-band Graphic Equaliser

I would start by checking the power supplies, they seem to be +-16 volts (Q1,Q2) with a seperate +16 volt supply (Q3)

[Nevillet]

Re: Yamaha Q2031A 31-band Graphic Equaliser



All the readings were reference to the chassis. All of the readings were positive values.

[R_J]

Re: Yamaha Q2031A 31-band Graphic Equaliser

Your problem is in the negative supply, Check the voltage across C3, if it is around 20 volts, it is likely R4/R2 are open, If there is 0 volts across, C3, check D2 & D4

[Nevillet]

Re: Yamaha Q2031A 31-band Graphic Equaliser

What a clever chap you are RJ.

Both are o/c although they look outwardly fine.

R2 should be a 15Ω 1/4W
R4 should be a 6.8Ω 1/4W

They are in parallel for a specific reason so I'm assuming a 4.7Ω 1/2W wouldn't do the same job?

[R_J]

Re: Yamaha Q2031A 31-band Graphic Equaliser

That should be fine, Do the resistors look burnt? if not they likely just went open over time. Monitor the negative voltage when you first turn it on in case there is something on that line that is shorted.

[Nevillet]

Re: Yamaha Q2031A 31-band Graphic Equaliser

There is evidence of heat in the area, but the resistors don't look burnt/chard.

These resistors are soldered floating above the PCB to help with with the thermal dissipation i'm assuming.

[Nevillet]

Re: Yamaha Q2031A 31-band Graphic Equaliser

Replaced the two resistors with a 4.7ohm and it's its working again.
Many thanks for your help

[R_J]

Re: Yamaha Q2031A 31-band Graphic Equaliser

Good to here it's working, thanks for letting us know, glad I could help.