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Another Yamaha SPX Power Supply Thread Multi-Effects Processors (HW)
Old 16th September 2017
  #1
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Another Yamaha SPX Power Supply Thread

So I got a dead Yamaha SPX 90, and I also have the schematic. Unfortunately the service manual does not tell me what voltages I should expect to see where.
So maybe someone here can help with that?

In the service manual schematic (attached), on page 26, looking at the "Japanese, US, and Canadian Models" power supply section, I am wondering what voltage I should see on the output of the rectifier D1. I get about 60V AC in on each (must be) input leg and it seems like nothing useful on the output legs. I assume I should expect DC on the output? I am using a digital multimeter to try to read the values.

Thanks for the advice. I am still learning.

Clay
Attached Files
File Type: pdf yamaha_spx90_service_manual.pdf (6.78 MB, 120 views)
Old 16th September 2017
  #2
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Anyone?
Old 16th September 2017
  #3
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It's better to measure the voltages at the output connectors from the PS. That should be connectors CN4 and CN5. There is also an analog supply for the audio components which is +/- 15V and one for +5V. The schematic is actually incomplete - search around to see if you can find a better one.
Old 16th September 2017
  #4
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Quote:
Originally Posted by Vitalis View Post
It's better to measure the voltages at the output connectors from the PS. That should be connectors CN4 and CN5. There is also an analog supply for the audio components which is +/- 15V and one for +5V. The schematic is actually incomplete - search around to see if you can find a better one.
I had measured the pins at the two connector blocks on the PS board, CN3 and CN4. No CN5 here. Strange that they call out a CN5 in the schematic. On CN4 I get nothing but 0.000v. The best I can find on CN3 is about -0.016v. See the PS images below.

I am wondering about that rectifier chip because the voltage seems to stop there. I see 60v on each pin on what I assume is the input side, and some variation around 0.05v on the output side when measuring in DC volts. If I measure that on AC I get about 24v.

I thought the output from the rectifier should be a rough DC? I can't seem to find any stable DC voltage beyond that device. I am measuring referenced to chassis ground by the way.

Oh, and the cut in the C11 capacitor insulator I made.

Thanks.
Attached Thumbnails
Another Yamaha SPX Power Supply Thread-yamaha_spx90_ps_us_1.jpg   Another Yamaha SPX Power Supply Thread-yamaha_spx90_ps_us_2.jpg  
Old 17th September 2017
  #5
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I checked across the output (positive and negative pins) of the rectifier chip. It gives me 112v DC. I have another SPX90 (II) that works, and the voltage across that rectifier is 165v. I'm still thinking the rectifier might be the problem.

What are the thoughts on that difference?

Thanks.
Old 17th September 2017
  #6
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Ok, so since I get practically no voltage on R4 and R5, I think I can conclude that the capacitor C11 must be bad.

I am still curious why the difference in voltage on the rectifier outputs of the SPX90 vs the SPX90II.
Old 17th September 2017
  #7
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crosscutred's Avatar
If a capacitor looks like that it's not worth saving the pennies for a new one, just replace it.

The voltages could be different due to different circuit design, or the bad cap could be pulling the voltage down.
Or something else.
Old 17th September 2017
  #8
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The voltage on the output of the rectifier should be 115 x 1.414 = 162VDC. 112VDC is way too low. The question is whether the rectifier is defective, or, there are other components bleeding off current to ground - in other words, dragging the rectifier voltage down. Check that out and if you can't find anything, then pull the rectifier.
Old 17th September 2017
  #9
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crosscutred's Avatar
If it was me, I would recap the whole power supply and see what was happening then.
It's worth putting a new battery in while you've got the board out.
Old 17th September 2017
  #10
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Quote:
Originally Posted by crosscutred View Post
The voltages could be different due to different circuit design, or the bad cap could be pulling the voltage down.
Or something else.
Yes, I have ordered new capacitors. I too wondered if it might be the capacitor affecting the output voltage reading from the rectifier But I don't think that's going to do it by itself. Maybe the transformer T1 is shorted. I got another rectifier chip also ($0.50), just in case.

In fact, after removing the capacitor the rectifier voltage output still shows 112v or so.

I can disconnect the R2 resistor to isolate the rectifier output. So if the output still shows 112v or so with nothing attached on the output side, it would be safe to assume a bad rectifier. Right?

Thanks.

And Vitalis, thanks for that calculation.
Old 17th September 2017
  #11
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crosscutred's Avatar
Can you measure the ac from the transformer?
Is that doing what you expect?
Old 18th September 2017
  #12
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The problem is not a cap failure, but I'll leave you two guys to get on with it - good luck.
Old 18th September 2017
  #13
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Quote:
Originally Posted by Vitalis View Post
The problem is not a cap failure, but I'll leave you two guys to get on with it - good luck.
Come now. The more the merrier.
Old 18th September 2017
  #14
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A couple of things.
You do understand this is a switching power supply?
The Electrolytic Capacitors are usually the first things to go bad.
I would replace all the electrolytics first, then get measurements.
And it appears they have referred to the 8 pin connector as both CN5 and CN3.

Denny
Old 18th September 2017
  #15
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Quote:
Originally Posted by dfchandler View Post
You do understand this is a switching power supply?
Yes indeed. I have seen it said many times. I don't know what "switching" refers to however at this point.

I have capacitors coming...

I am very interested to find the cause of the problem. Good to learn about.
Old 19th September 2017
  #16
A switching power supply use semiconductor to switch (on and off) the power to regulate the voltage and current at the output.
A linear power supply use the classical structure power transformer=>diode bridge rectifier=>electrolytic capacitor=>linear voltage regulator

You can see it like the difference between analogic and digital audio.

You can quickly see the difference between the two in the transformer, linear power supply require a bigger power transformer to deliver the power.
As dfchandler point it out it's the capacitors that are frequently the first to go bad.
Another point you need to know is switching power supply frequently deal with the main voltage so BE CAREFUL when you try to repair, main voltage are dangerous and the power it can deliver is huge!
Old 22nd September 2017
  #17
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Quote:
Originally Posted by wavenurse View Post
A switching power supply use semiconductor to switch (on and off) the power to regulate the voltage and current at the output.
A linear power supply use the classical structure power transformer=>diode bridge rectifier=>electrolytic capacitor=>linear voltage regulator
Thanks for that.

Looking at the output of the rectifier IC I get 111v DC across the negative and positive pins, whereas when checking on my working spx90II I get 165v DC. I have also removed the connections that go further downstream in the circuit, in case something was draining it to ground, to isolate the IC and I still get 111v DC.

So, if indeed 111v is too small, then one of the few components on the AC side of the IC could be an issue? The problem is, I get 120vAC across the AC side at the IC.

How could I tell if something is weak; just strong enough to red 120v AC but not strong enough to properly power the rectifier IC. Is that a possibility?

This is baffling. Ideas?
Old 22nd September 2017
  #18
Do you changed the capacitors?
If not, it's the first thing to do.
If it's done, check the output voltages of the supply.
Don't focus too much in comparing the two supply.
Fabrice.
Old 23rd September 2017
  #19
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Quote:
Originally Posted by wavenurse View Post
Do you changed the capacitors?
If not, it's the first thing to do.
If it's done, check the output voltages of the supply.
Don't focus too much in comparing the two supply.
Fabrice.
I have only changed the C11 capacitor, but since the voltage seems low going to that, I have to wonder how the other caps further downstream would be the issue. In fact, I really get about 0 volts DC at the C11 capacitor. I replaced the rectifier IC with one I am hoping is similar, but that didn't make it work, and have since put the original back in.

I could change them, but I feel like that would be a waste if there is some more serious problem, i.e., the inductors L1 and L3. The capacitors around those are ceramic, long brown ones in the photo above.
Old 23rd September 2017
  #20
Do you have some AC after L1 if it's ok then check for AC after L3 and then for DC after D12 and so on... Follow the schematic!
For the electrolytic capacitors it's common to replace them all because because after so many years they have dried. Sometimes they act as a short circuit sometimes they simply accumulate no electric charge and increase their internal resistance.
It is a good practice to replace them all.

Fabrice.
Old 23rd September 2017
  #21
But you are true if there is no current and no voltages that going to c11 there is a problem before it.
Check also diode bridge D1.
Old 23rd September 2017
  #22
There is a lot of scenarios that can happen with this type of power supply and it's not so easy to repair it!
Old 23rd September 2017
  #23
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Quote:
Originally Posted by wavenurse View Post
But you are true if there is no current and no voltages that going to c11 there is a problem before it.
Check also diode bridge D1.
I get 120v AC across the input side of the rectifier IC, which indicates to me that all component upstream are supplying what they should, at least regarding the voltage. I get 111v DC on the output side of the rectifier, which I understand is too low (should be around 165v DC). Replacing that rectifier didn't make it work, but I didn't check the output voltage. I will replace it again and check the output voltage and see if it changes.
Old 25th September 2017
  #24
You can also consider to change the complete power supply by a new linear one?

Old 26th September 2017
  #25
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Quote:
Originally Posted by wavenurse View Post
You can also consider to change the complete power supply by a new linear one?

What's that gonna cost me? Where is one?

Thanks.
Old 4th October 2017
  #26
Approximately 85 euros so 100 us dollars including vat. But you need to build it completely and etch and drill your own pcb.

Fabrice.
Old 5th October 2017
  #27
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Quote:
Originally Posted by wavenurse View Post
Approximately 85 euros so 100 us dollars including vat. But you need to build it completely and etch and drill your own pcb.

Fabrice.
Too bad. A Yamaha SPX90 isn't worth all that.
Old 5th October 2017
  #28
Okay, but the spx90 is no longer produced, so any model you can find on the net will have this power problem, it's a matter of time!
But I understand your point of view.

Fabrice
Old 7th October 2017
  #29
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Quote:
Originally Posted by wavenurse View Post
You can also consider to change the complete power supply by a new linear one?

Do you know if anybody who did one of those used an actual etched PCB and might have layouts? My switching PS was recapped and resurrected, but I've wondered if that might be worth trying.

Thanks!
Old 7th October 2017
  #30
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Quote:
Originally Posted by lahatte View Post
Too bad. A Yamaha SPX90 isn't worth all that.
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.
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