Yamaha M4 problem.

[pmwinrammy]

Hello folks,

I am hoping someone can help me. I have just recapped the power supply of my M4 power amp.

I put 100 uf electrolytic and 0.1 uf film bypass caps across the 15000 uf reservoir caps, unfortunately I got the polarity wrong on one of the 100 uf electros.

Out come the magic smoke and I switched of pretty quickly. I found and removed the incorrectly fitted cap. However when I now power up the LED VU meters show some green lights and the red overload warning is lit up, this is on both channels.

Power to the amp boards is good at +/- 65v and bias is ok at +/- 16 mv.

Can anyone point me in the right direction of what might need checking replacing?.

Thank you.

 

[clinic-audio]

Did you check voltage from power suplly going to indicator PCB ?

 

[avionic]

What is your voltage on the main caps now with reference to ground ?(unregulated B+ and B- ) May have damaged bridged rectifier D601/D602.

I put 100 uf electrolytic and 0.1 uf film bypass caps across the 15000 uf reservoir caps,

Why ?

 

[pmwinrammy]

Thank you both for taking the time to reply.

I powered it up again today and it went from partial VU lights with red overload to no lights showing, The speaker relays do not click in so there's still a problem.

I measured the supply to the VU meters and there is now no voltage present.

Main reservoir caps are +/- 60 v.

The +/- 80 v to the amp boards is reading +/- 92 v.

Tried to remove the metal covers over the diodes to have a look at them but they are not moving, I've removed the solder but they won't budge. Any tips?.


To answer the why question, I have always bypassed large value caps. Normally without any problems, I guess this time I got a bit sloppy.

 

[avionic]

Tried to remove the metal covers over the diodes to have a look at them but they are not moving, I've removed the solder but they won't budge. Any tips?.

Those so called "metal covers" are the junction of those dual diodes. You probably still need to unsolder the two diode pins under each of the dual diodes.

 

[avionic]

Main reservoir caps are +/- 60 v.

Those diodes are OK.

 

[avionic]

I powered it up again today and it went from partial VU lights with red overload to no lights showing, The speaker relays do not click in so there's still a problem.

Check the DC balance/offset voltage on both of the amplifier boards.

 

[avionic]

http://audiokarma.org/forums/index.php?threads/yamaha-m-4-dc-offset.120404/#post-1273240

 

[avionic]

The speaker relays do not click in so there's still a problem.

Do you have at least one of the speaker front panel buttons depressed ? If not ,you won't get a relay "click".

 

[pmwinrammy]

Sorry for my late reply . I won't get chance to check the DC offset till weekend (damned work) .

Both A / B buttons pushed in but no relay click . Relays were replaced around 12 months ago so there shouldn't be a problem there .

I will have another look at it at weekend , thank you for your help .

 

[clinic-audio]

Sorry but the question is for us to know if there is any DC OFFSET at the output making no click with both relays (A or B) . This is not a question of old or new relays .You perfectly may have DC OFFSET with new relay .
Waiting to know more