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Yamaha EMX512sc Power supply fixed!

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Joined: 24 Jan 2013
Posts: 4

PostPosted: Thu Jan 24, 2013 4:45 pm    Post subject: Yamaha EMX512sc Power supply fixed! Reply with quote

I just managed to fix a Yamaha SMPS board today after hours of work so I thought I'd share with esi visitors.
It is a Yamaha EMX512sc mixer/amp (similar to the EMX312sc)
Yamaha will send you the schematic if you ask but you can find it on here.

If the switch mode power supply outputs fail for any reason, the 15 volt primary side supply depends on the linear regulator circuit around Q414. This circuit has to drop approx 305 Volts across R440 and Q414. It is only designed to run for a split second to bootstrap the main supply from a winding on the transformer. If the main switch mode supply does not start, the usual result is that R440 burns out and Q414 is damaged.

On my board, Q414 seemed to test OK with a meter but it must have been leaking because R440 kept burning out. I ended up replacing the following and I recommend you do the same, even if they seem to test OK.

R440 220 Ohm 2W
IC403 78M15FA - 15 Volt regulator
IC401 SG3525AN - smps controller
IC402 L6385 - driver dip8
Q406, Q407 IRGB15B60KD - IGBT

The service manual also suggests you check the following parts too (in my case, they were OK)
R419,R421 33 Ohm
D404,D405 diodes
R418,R424 6.8 Ohm 5W, soft start resistors
R429,R430,R453,R454 1 Ohm
F401 T6.3 A (for 240 Volt)


Good luck.
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PostPosted: Sat Mar 22, 2014 10:03 pm    Post subject: R443 & 445 Reply with quote

Yes, an interesting design! Thanks for the info and your very good advice - agreed.

Can you help please - I am puzzled on the values of R443 & 445. In the schematic of the Service Manual they are 15K & 10K respectively, but in the unit I am repairing (512SC, H variant PSU) they are both 33K. Not indicated on the schematic as model-variant dependent values.

I would like to know if I should change them to 15 & 10K, if that's a later revision, or if 33K's are the values that are later? I can't see any revision code on the PCB or in the Service Manual, but I don't know where to look for that info. Any ideas what/where to look for?

I have the schematic (obviously) but I noted that you mentioned asking Yamaha for one. If the best way to get my question answered is to ask them then I would very much appreciate advice on how to contact a person there who could help with that level of detail. (I'm in the UK, if that makes a difference.)

Many thanks.
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Joined: 02 May 2014
Posts: 1

PostPosted: Fri May 02, 2014 10:28 pm    Post subject: Reply with quote

Thank you...useful info. Smile
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Joined: 07 Aug 2014
Posts: 1

PostPosted: Thu Aug 07, 2014 3:32 am    Post subject: R418 and R424 always burn and damage Reply with quote

can you help me please, i was replace All IGBT transistor and several resistor but always failed (R418 and R424 is burn and damaged)
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