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SPX90 Power supply schematic Q1, D6 & D7
Old 5th January 2015
  #1
Gear Nut
 

SPX90 Power supply schematic Q1, D6 & D7

Hi all,

I'm trying to repair my Yamaha SPX90 (Mark 1) power supply.

Besides recapping I have noted which other parts need replacing. Q1, D6 & D7.

Link to manual & Schematic (Pages, 18 & 26-27):

https://www.google.co.uk/url?sa=t&rc...,d.d2s&cad=rja

However the Manual (page 18) lists the various electrical components but I'm not sure how to figure out which ones they are referencing and the equivalent component I can order for replacement. Perhaps someone who has replaced these parts successfully could let me know the correct values.

As marked on the schematic (pages 26 & 27):

Q1: Transistor (blown)

D6: Diode on the (+) rail (blown)

D7: Diode on the (-) rail, I ought to replace this one as well.

Thanks,

Aaron
Old 5th January 2015
  #2
Gear Addict
 

I don't know the unit at all, but it looks to me like page 18 (as printed, not Adobe Reader) shows those parts.

Q1 - 2SC2555
D6, D7 - 15DF2, 15DF4

SWPS scare me.They can be tricky. Make sure the replacement caps are low ESR, high temp for SWPS.
Old 5th January 2015
  #3
Gear Nut
 

Thanks GLouie,

I'll check out that info.

I suppose this infamous failing Yammie power supply is kind of like Monty Python's Rabbit of Caerbannog. When I popped the hood it just looks so innocent and cute...yet many a better man than I have fallen to it's trickery.

Cheers,

Aaron
Old 6th January 2015
  #4
Lives for gear
 
LeeYoo's Avatar
 

Hi Aaron
Warning. SMPS repair is not for beginners..
First thing to do is to make sure the rest of the unit still works with another supply.
I suppose you could even use an old +/-12 /5v computer supply for that.
No point in fixing the supply if the rest is damaged.
No need to disconnect anything. Just connect the right voltages to the right rails.
D6/D7 could be replaced with common 40 or 60 volt/ 1Amp schottky diodes.
Q1 has to be the right one.
Before you replace, check every part in the snubber network. D2, R6, C74!. And R13.
Test the supply with secondary loads disconnected, or better, with some resistive loading.
Be safe.
Leo..
Old 6th January 2015
  #5
Gear Nut
 

Hi Leo,

Thanks for your post.

I do agree that this job is definitely not for a beginner. I will read up on all the information that has been provided for me and online as well. When there is a bit of time between work I will enlist the aid of a very experienced good friend to assist me in learning about how to implement this knowledge and test this power supply safely.

I am very keen to learn new knowledge about power supplies...if the SPX lives to record another day that will be a bonus...if not I can use it as a higher status door stop than my Behringer v-verb! - I guess those crackling outputs will be next on the list eh?

Thanks,

Aaron
Old 29th January 2016
  #6
Gear Maniac
 

Spx 90 psu

I just brought a SPX 90 on line Was not in the best condition. when it arrived it had rust and some serious noise on the outputs. as a little project I sanded it down and resprayed it. Then to fix the noise the power supply was screwed and i did not want to deal with it. ( recapping, finding right parts and) so i built my own linear supply for it. works great now no noise at all.
if your ok with electronics I would reccomend building your own linear power supply for it.
some will probably say its not worth it but it was fun.

Josh.
Old 13th October 2016
  #7
Here for the gear
 

For D6 & D7 I've used 1N4936 diodes.

For Q1 either 2SC2555 or 2SC2792.
Those also have NTE equivalents, NTE2308 and NTE2309.

Be forewarned if something is really wrong with the supply, a new Q1 will blow almost instantly.

Last edited by QuestingElf; 13th October 2016 at 06:16 PM.. Reason: emphasize new
Old 21st February 2020
  #8
Lives for gear
 
StepLogik's Avatar
My trusty SPX90 (mark 2) is getting flaky. I'm pretty sure it's the PS. Has anyone ever sourced a drop-in replacement (meanwell, etc)? I can certainly rebuild it but it seems like a lot of bother when there's so much available off the shelf.
Old 21st February 2020
  #9
Gear Maniac
Unless someone has done the legwork to come up with a drop-in upgrade (like the Linndrum and other vintage machines worth way more money), I think the best is to get a recap kit online (eBay) and change out the electrolytics on the PSU and clean up the board. That should solve problems in 90% of the cases (a guess obviously). If there are blown semiconductors too, then things get ugly fast. I had a resistor that needed replacing and I think a ceramic cap too. Not sure, but I probably reported it in one of these threads.
Old 21st February 2020
  #10
Sometimes these have a fried switching transformer. Then the replacement switch transistor won't fix it. You will probably need a transformer from Yamaha if available.

These can be quieted down by using very low impedance filter caps, both on the power supply pcb and the main pcb before the regulators. I use Panasonic FR caps, the largest that can fit. Secondary caps past the regulators are 1000 uf/25V FR's. Bypass all of them with 100V .1 uf mono ceramics.
Old 21st February 2020
  #11
Lives for gear
 
StepLogik's Avatar
It looks like the only application-specific features of the PS are the optoisolator heartbeat for the mute circuit. I haven't pulled my SPX from the rack yet but once I get it apart and look at the board I should have a better idea of how bad it is.
Old 21st February 2020
  #12
Lives for gear
 
StepLogik's Avatar
Quote:
Originally Posted by Blissy View Post
I just brought a SPX 90 on line Was not in the best condition. when it arrived it had rust and some serious noise on the outputs. as a little project I sanded it down and resprayed it. Then to fix the noise the power supply was screwed and i did not want to deal with it. ( recapping, finding right parts and) so i built my own linear supply for it. works great now no noise at all.
if your ok with electronics I would reccomend building your own linear power supply for it.
some will probably say its not worth it but it was fun.

Josh.
What did you use for the regulation? I'm assuming 7805 (and a big heatsink) and did you spec something for the 18v rails or use a different output voltage? How much isolation between the analog/digital?
Old 21st February 2020
  #13
Lives for gear
 
StepLogik's Avatar
... and I should cut in an IEC connector while I'm at it. Never liked those attached power cords on old Yamaha rack gear.
Old 1 week ago
  #14
Gear Head
 

Quote:
Originally Posted by StepLogik View Post
What did you use for the regulation? I'm assuming 7805 (and a big heatsink) and did you spec something for the 18v rails or use a different output voltage? How much isolation between the analog/digital?
I am also embarking on a similar mission regarding a linear PSU. Have you made any progress? If so, are you able to share the fruits of your labour?

Cheers.
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