Wx7 service repair manual

This section covers the WX5/WX7/WX11

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rbond
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Re: Wx7 service repair manual

Unread post by rbond » Sun May 13, 2018 1:13 am

... I love forums... thx for keeping this thread alive :D

Like others here... I'm looking to repair my WX7 Power Supply. Not only did the battery contacts get grossly corroded... but the unit doesn't function with the wall wart either. Taking it apart revealed why... and now I'm looking for the IC number... as you can see in the pic... mine exploded 8O

My PS is not labeled as the BT7 however... and not certain of any difference between that and my generic (original?) unit.

Cloudburst... does the shop manual identify the IC #? Mine ends with xxx4K
Caps look ok... but I'll probably replace them as well in my "rebuild".

The first question should be "Why?" ... and I'm a bit suspect because the wall wart (YA-1) is putting out 14.6vdc when it's rated at 12v... but I can't imagine that 2 volts is enough to pop an IC.

Anyone else have thoughts re. rebuilding these little units?

thx again!
Russell
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Saul
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Re: Wx7 service repair manual

Unread post by Saul » Sun May 13, 2018 1:44 am

Hi Russell, welcome to yamahamusicians.com :) and thanks for taking time to post those images. I think that will definitely help others with similar problems.

It might not sound a lot but running 14.6v into a 12v device will cause problems. As far as I am aware and I am sure people here with more knowledge will clarify, most electrical devices can handle a small surge in power over a very short period but not a consistent over voltage. And I think this popped IC is a direct result of a faulty adapter.

Can't say for sure but I would imagine that IC or it's equivalent would be easy to get hold of but perhaps someone else can confirm what type and number it is?
Saul
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Miks
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Re: Wx7 service repair manual

Unread post by Miks » Sun May 13, 2018 9:29 am

Those are voltage regulators - the one shown in the above picture is either a "7808" or a "7908" as you can see the 7?08 in the inscription:
VoltageRegulator.jpg
VoltageRegulator.jpg (38.12 KiB) Viewed 674 times
These common parts are cheap to buy.

Edit: here's a pic where the part is shown (same type of power supply!):
VoltageRegulator2.jpg
VoltageRegulator2.jpg (39.14 KiB) Viewed 674 times
So the part you'll need to buy is a "7808 voltage regulator" aka "µA 7808" :wink:
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Re: Wx7 service repair manual

Unread post by Buzzard » Sun May 13, 2018 9:56 am

The blown IC could be a voltage regulator.

Unfortunately, it's not possible for me to determine the exact type since some of the numbers are missing.

:idea: IF it was a 7808 , it was a POSITIVE voltage regulator, or a 7908 NEGATIVE voltage regulator. :idea:

Find out EXACTLY what the part it is and replace it with a new equivalent part, they're cheap, guessing 1-2 usd.

I've used voltage regulators in some of my own creations, notice the two regulators in the picture.
voltage regulator.jpg
It used to be a home made transistor guitar amp, needing a +8 , 0 , -8 power supply, using both a positive and negative voltage regulator

Regards
Peter
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rbond
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Re: Wx7 service repair manual

Unread post by rbond » Mon May 14, 2018 6:09 pm

... thx for the input, gents...

Saul... good thought on the AC adaptor... and now that I think about it... when this unit is powered by battery, it's only running 9v (6 x 1.5)!!
So 14.6 is WAY hot for this thing. I only ASSUMED that the YA-1 AC adaptor that was in the WX7 case was the correct one 8O

Does anyone know for certain if the YA-1 AC adaptor is the right one? Spec is DC 12v, 300mA ... or is the correct adaptor only 9v?

Miks- thx for the 7808 pic and info... that helps! As you can see, the second set of numbers on the reg in my unit is different from the one in your pic... yours is 8802K ... where mine ends in xxx4K. Any significant difference?

Buzzard... nice breadboard job! :wink: I'm definitely trying to sleuth out the correct part... the pic that Miks posted is a good clue! But I believe you're correct... looks like an 8v regulator.

Again... the power/midi interface pack I have is not labeled as the BT7... but perhaps that's just a re-branding of the original unit (?)

Cheers!
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Miks
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Re: Wx7 service repair manual

Unread post by Miks » Mon May 14, 2018 9:54 pm

rbond wrote:As you can see, the second set of numbers on the reg in my unit is different from the one in your pic... yours is 8802K ... where mine ends in xxx4K. Any significant difference?
No - that might be the manufacturing date: 88 = year, 02 = week, K = ? maybe a kind of 'charge number' - or a 'code' for the factory that has manufactured this part...

If I were you I would buy a replacement that could deliver 1.5 ampere or 2 ampere (see specs of the new part) - just to be 'on the safe side'. And some thermally conductive paste applied between voltage regulator and heat sink wouldn't hurt too... 8)
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Re: Wx7 service repair manual

Unread post by Buzzard » Tue May 15, 2018 8:20 pm

Just to sum it up. :wink:

Thanks Miks, for finding a picture of an undamaged power supply, confirming that the part is indeed a 7808.
You were spot on. :D
The other numbers and the brand name is irrelevant, any quality 7808 will do.
Do install the new 7808 with thermic paste to distribute heat to the heat sink.

The power supply should be a 12volt dc , positive at the tip.
300ma sounds sensible, but do check the manual, it may need more power, or can do with less.
A 13.4 volt power supply may work, but don't risk it.

Running the unit on batteries at 9volt , is no surprise.
Without having seen a circuit schematic,
I guess that even the battery voltage runs through the 7808 delivering 8volts to the circuit.

While you're at it, look carefully to check if any other parts fried.
That includes any capacitors that have expanded, or leaked.
If not, you should be good to go once the new voltage regulator is installed.

Regards
Peter
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Re: Wx7 service repair manual

Unread post by rbond » Tue May 15, 2018 10:42 pm

... a very sincere thank you, gents... I'll report back with my results... and/or further issues! :D
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Re: Wx7 service repair manual

Unread post by cloudburst » Sun Jun 10, 2018 6:35 am

Here’s a circuit diagram of the BT7.

CB
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Re: Wx7 service repair manual

Unread post by sloanefreeman » Fri Jun 29, 2018 3:13 am

Does someone know the Yamaha part number for the WX7/Wx11 reed?
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Re: Wx7 service repair manual

Unread post by cloudburst » Tue Aug 21, 2018 8:45 am

sloanefreeman wrote:
Fri Jun 29, 2018 3:13 am
Does someone know the Yamaha part number for the WX7/Wx11 reed?
VD443100

CB
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