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Another Yamaha SPX Power Supply Thread
Old 1 week ago
  #31
Gear Nut
 

Thread Starter
Quote:
Originally Posted by Scoobis View Post
there are plenty of switching power supplies on ebay that would likely fit and work, didnt take me loing to do a quick search and come up with a few that were +/- 15v and +5v

even a meanwell branded ones were under 40 bucks. id bet you could find something that would fit inside and supply enough current if you did some searching.
Good thought. It would be nice though if I could fix this one. Good knowledge, and good for the ego.

Of course, I still need some guidance.
Old 1 week ago
  #32
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crosscutred's Avatar
I would keep working on fixing the existing unit.
It can't be that hard, you've narrowed it down quite a lot.
Old 1 week ago
  #33
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wavenurse's Avatar
Quote:
Originally Posted by Scoobis View Post
there are plenty of switching power supplies on ebay that would likely fit and work, didnt take me loing to do a quick search and come up with a few that were +/- 15v and +5v

even a meanwell branded ones were under 40 bucks. id bet you could find something that would fit inside and supply enough current if you did some searching.

Yes you are true, but you need to modify it because there is an opto transistor on the original supply that mute the output if not present. But it's an alternative to the linear power supply surely!
Old 1 week ago
  #34
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Quote:
Originally Posted by crosscutred View Post
I would keep working on fixing the existing unit.
It can't be that hard, you've narrowed it down quite a lot.
I am pretty much at a loss for what to do next. I could replace all the other capacitors, but I don't see how that would fix it, since I don't seem to be getting proper voltage at C11.
Old 1 week ago
  #35
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crosscutred's Avatar
Just replace all the capacitors in the power supply section, it's not going to break the bank, have a look at the other parts in the power supply too. Maybe order them while you're at it.

Even if you have to replace all the components except the transformers it will work out cheaper than a new switching supply.
Old 1 week ago
  #36
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Thread Starter
Quote:
Originally Posted by crosscutred View Post
Just replace all the capacitors in the power supply section, it's not going to break the bank, have a look at the other parts in the power supply too. Maybe order them while you're at it.

Even if you have to replace all the components except the transformers it will work out cheaper than a new switching supply.
I am wondering how I can test the transformers. I understand that it can be sometimes difficult to test properly without a special tester.
Old 1 week ago
  #37
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crosscutred's Avatar
Quote:
Originally Posted by lahatte View Post
Quote:
Originally Posted by crosscutred View Post
Just replace all the capacitors in the power supply section, it's not going to break the bank, have a look at the other parts in the power supply too. Maybe order them while you're at it.

Even if you have to replace all the components except the transformers it will work out cheaper than a new switching supply.
I am wondering how I can test the transformers. I understand that it can be sometimes difficult to test properly without a special tester.
You are getting ac through the mains transformer, because it appears at the rectifier, so that is fine.
I haven't really had time to look at the schematic so I'm not sure what else is involved but if you start with recapping (could do with being done anyway to delay having to open it up again), test to see if it works, then start with replacing other parts. You have narrowed it down to a small number of components so even replacing every part on the board will probably come in cheaper than buying a whole new power supply and the hassle of getting that up and running.
Don't give up, it will be very satisfying when you get it running.
Old 1 week ago
  #38
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wavenurse's Avatar
Totally agree with crosscutred, if you want to repair you power supply, you need to replace all the capacitors first. In particular if you are not well equipped with measuring instruments, how can you say this cap is shorted or this one is ok!
You can do it
Fabrice.
Old 1 week ago
  #39
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Thread Starter
Quote:
Originally Posted by crosscutred View Post
You are getting ac through the mains transformer, because it appears at the rectifier, so that is fine.
I haven't really had time to look at the schematic so I'm not sure what else is involved but if you start with recapping (could do with being done anyway to delay having to open it up again), test to see if it works, then start with replacing other parts. You have narrowed it down to a small number of components so even replacing every part on the board will probably come in cheaper than buying a whole new power supply and the hassle of getting that up and running.
Don't give up, it will be very satisfying when you get it running.
Thanks guys. I will go ahead and replace all those caps when I can get to it.

But crosscutred, if you do get a chance to look at the schematic I would like to know your thoughts on the no voltage at C11.

Thanks very much.
Clay
Old 1 week ago
  #40
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Clay,

This is what was in mine in case you need dimensions or values. There's probably a Mouser order list around here of what actual parts I bought, but I'd imagine I had all sorts of other crap on the order too.

Keep in mind that as old as they are, even with a 100% working PS, you may realize that something else needs looking at on the mainboard. I think mine needed a couple caps there. They also get relay and jack issues with age if I'm remembering right.

Take Care
Attached Thumbnails
Another Yamaha SPX Power Supply Thread-spx90ii-power.jpg  
Old 6 days ago
  #41
Gear Head
 

Quote:
Originally Posted by lahatte View Post
Thanks guys. I will go ahead and replace all those caps when I can get to it.

But crosscutred, if you do get a chance to look at the schematic I would like to know your thoughts on the no voltage at C11.

Thanks very much.
Clay
if your not getting voltage across c11, check the resistance of r2 see if its open.

if R2 not open, and your not seeing voltage across c11, then check the doides in the bridge rectifier.
Old 6 days ago
  #42
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Thread Starter
Quote:
Originally Posted by Scoobis View Post
if your not getting voltage across c11, check the resistance of r2 see if its open.

if R2 not open, and your not seeing voltage across c11, then check the doides in the bridge rectifier.
I think indeed it may be R2. I have DC voltage from the rectifier at the 'in' side of R2, but none on the other side. Still strange it's only 110v DC, and not 165v or so. But, is it 6.8 Ohms, or 6.8k Ohms?? The schematic shows "6.8", but is that understood to be K Ohms? wait, nevermind. Printed on the resistor is "6.8 R K", so I assume 6.8K Ohms.

Looking at these as replacement...

Last edited by lahatte; 6 days ago at 04:49 AM..
Old 6 days ago
  #43
Gear Nut
 

Thread Starter
Ok. So here's something I just noticed (still new to reading schematics). I see on page 26 (right side) of the SPX90 schematic pdf that they show what the pins for the power board connections are for. So, I can get what is +18, +5, etc (volts), but I do not know what are these, and it would help to know... PC, PE, AG, DG.

Anyone know? Thanks.
Attached Files
File Type: pdf yamaha_spx90_service_manual.pdf (6.78 MB, 2 views)
Old 6 days ago
  #44
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Quote:
Originally Posted by lahatte View Post
I think indeed it may be R2. I have DC voltage from the rectifier at the 'in' side of R2, but none on the other side. Still strange it's only 110v DC, and not 165v or so. But, is it 6.8 Ohms, or 6.8k Ohms?? The schematic shows "6.8", but is that understood to be K Ohms? wait, nevermind. Printed on the resistor is "6.8 R K", so I assume 6.8K Ohms.

Looking at these as replacement...
ok so the resistor should be 6.8 ohms.

if its burnt out, then you have to figure out why it burnt out.

if its burnt out it was likely caused more then 5w of power to be dropped across that. that could be perhaps a shorted cap, or a problem in the switching circuit.

but were getting ahead of ourselves.

what did you read for a resistance for R2?
Old 6 days ago
  #45
Lives for gear
Quote:
Originally Posted by lahatte View Post
Ok. So here's something I just noticed (still new to reading schematics). I see on page 26 (right side) of the SPX90 schematic pdf that they show what the pins for the power board connections are for. So, I can get what is +18, +5, etc (volts), but I do not know what are these, and it would help to know... PC, PE, AG, DG.

Anyone know? Thanks.
AG- Analogue Ground
DG- Digital Ground
PC, PE- Connections from the opto on the PSU to the main board used to operate the mute relay on power failure (I think...!)
Old 6 days ago
  #46
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wavenurse's Avatar
PC PE are connections to the opto you are right londonengineer!
Old 6 days ago
  #47
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wavenurse's Avatar
PC connection to the Collector from the opto transistor of the optocoupler

PE connection to the Emitter from the opto transistor of the optocoupler

Old 6 days ago
  #48
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Thread Starter
Quote:
Originally Posted by Scoobis View Post
what did you read for a resistance for R2?
In circuit I read 0.0 ohms, so it would appear to be ok. I'll need to remove it to check properly.

The resistor has "6.8 R K" printed on it, which tells me 6.8K Ohms. Concur?

Thanks for the explanations of the connection codes guys.
Old 5 days ago
  #49
Gear Head
 

Quote:
Originally Posted by lahatte View Post
In circuit I read 0.0 ohms, so it would appear to be ok. I'll need to remove it to check properly.

The resistor has "6.8 R K" printed on it, which tells me 6.8K Ohms. Concur?

Thanks for the explanations of the connection codes guys.
again it is 6.8 ohms.

R usually indicates the decimal place. so its an odd marking for sure.

K in this case is the tolerance of 10% J would be 5%

6.8k would be labeled either 6.8k or 6r8k

yes, id agree, it seems you need to unsolder one side to check it. 0.0 is not right. it should read 6.8 ohms.

make sure the cap is discharged before you try and unsolder the resistor, i wouln't want you getting hurt.

remember your dealing with lethal voltages and currents here even when its off and unplugged.
Old 5 days ago
  #50
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Thread Starter
Quote:
Originally Posted by Scoobis View Post
K in this case is the tolerance of 10% J would be 5%
Ah, yes. That makes sense. Thanks. The other one, R13, has "1 [Ohm symbol] K", so that would be 1 Ohm.

Quote:
Originally Posted by Scoobis View Post
yes, id agree, it seems you need to unsolder one side to check it. 0.0 is not right. it should read 6.8 ohms.
Doh! Sorry about that brain fart. Indeed, a good resistor wouldn't read 0 ohms. I disconnected R2 and and it is indeed open.

So while I wait for the new part to arrive, I suppose it would be good to see if there is something that caused R2 to fail. Thoughts on that?

Thanks.
Old 5 days ago
  #51
Gear Head
 

So yea, this is where the can of worms starts.

so many things can cause that. and sometimes has a cascading effect.

you could easily have taken out the transistors and the bridge rectifier.
do start with checking the bridge rectifier, check the cap c11, check the transistors.

with any luck, c11 is shorted, and, the bridge rectifier is bad. that explain everything.

it bother me you read 0 ohms across the resistor at first, that makes me think there is a dead short someplace that shouldn't exist.

just and fyi, so you could change out a lot of bad parts, and plug this in and fry all the new parts you put in if you don't find the root cause.

anyway c11 and bridge rectifier. ... check those .. if you don't know how just let us know.
Old 5 days ago
  #52
Gear Nut
 

Thread Starter
Quote:
Originally Posted by Scoobis View Post
it bother me you read 0 ohms across the resistor at first, that makes me think there is a dead short someplace that shouldn't exist.
Yea, I was thinking that this morning.

I have already changed C11 and the rectifier. If I recall correctly, I had C11 out when I tested the voltage from the new rectifier, which was still 110v DC, not 165v as my other unit (SPX90II) showed for that, and what the formula says it should be.

I am going to first look for how something could short across R2. Will report back after I look.
Old 5 days ago
  #53
Gear Head
 

its possible q1 and q2 are bad, but, i don't see how you would read 0 ohms even if they were. 1 ohm would be the lowest i think, as best i can judge.

besides .. you need to check those transistors anyway.

while your in there, check the diodes in the circuit.
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