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Author Topic: Yamaha PC4002M blowing fuses/output transistors  (Read 901 times)

ilyaa

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DrGonz78

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #16 on: July 15, 2017, 02:52:59 PM »

Try this out. It seems Digikey is now my go to for Sanken type transistors.

https://www.digikey.com/products/en?keywords=2sa1294

https://www.digikey.com/products/en?keywords=2sc3263
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A person who never made a mistake never tried anything new. -Albert Einstein

ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #17 on: July 15, 2017, 09:21:19 PM »

any reason those ones i posted links to wouldn't be suitable replacements?

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Enzo

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #18 on: July 16, 2017, 01:24:38 AM »

They would probably be fine, just do not mix the types.
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ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #19 on: July 31, 2017, 02:52:19 PM »

alright guys we are almost there!

re-transistored the whole amp (the bad channel, that is) and we seem to be powering up and no-load idling just fine at the same idle draw as the other channel.

only thing is, before i send anything through it, i'd like to replace the green thermal tape behind the output transistors. its gone through some trials and tribulations and there was at least one bare spot that shorting B+ to B- through the case of one of the output transistors. i dont have any of this stuff around - RIP radioshack and the electronics store in town doesn't carry it -

any suggestions where to look for it (non-internet) or what kind of tape works for this purpose?
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ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #20 on: August 07, 2017, 11:51:08 AM »

no one have any thoughts on where to get green heatsink tape?

all the stuff I'm finding is double-sided and made for ICs - comes in squares

the tape on the Yamaha output transistor heatsink is greenish and one-sided and clearly comes in a roll -
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galaxiex

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #21 on: August 07, 2017, 12:48:16 PM »

no one have any thoughts on where to get green heatsink tape?

all the stuff I'm finding is double-sided and made for ICs - comes in squares

the tape on the Yamaha output transistor heatsink is greenish and one-sided and clearly comes in a roll -

Maybe some Kapton tape? probably not available local to you...

How about some Mica insulators?
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Enzo

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #22 on: August 07, 2017, 11:43:25 PM »

Well don't call it tape, that will surely confuse the search.

Bergquist SilPads is probably the best know brand name.

Transistor mounting supplies
Transistor insulators

I have never seen it in rolls.  I usually see them precut for various transistor sizes, complete with hole for mounting screw.

It also comes in sheets so you can cut it to size.

Search "thermal interface products" at Mouser.
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ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #23 on: August 09, 2017, 02:03:01 AM »

k think I'm gonna go with the insulators -

man this amp fix is never ending!
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ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #24 on: August 17, 2017, 04:15:03 PM »

we did it!

alright rebuilt most of this damn thing -

the heatsink may have been a big issue - i noticed some spots where it had either melted or blown up a little bit and i think this may have been causing some arcing/shorting!

but ran both channels at 75 watts for quite a while and we're all good.

NOW for the final question:

i was fixing this up for a studio in town. they are using it as a - and i'm not kidding - headphone amp. im wondering, should i talk them out of this usage altogether? or is there a way to make it work? they had their tech put a 4 ohm 25W resistor in series with the + speaker lead and otherwise just hook it directly into headphones. the headphones they are using are 38 ohms that can handle 1.5W. now if they run it at low wattage it should be okay, BUT

1) the VUs on the front are for watts/8ohms - with this setupt the amp is seeing 42 ohms  - is there a way to calculate the adjusted wattage
2) would it make more sense to also wire a high wattage 8 ohm resistor across the output jacks so that the impedance matches more closely?
3) is this a silly path to take? i think the engineer just really likes this amp but im not sure i see the point of using a high wattage power amp on headphones....
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Enzo

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #25 on: August 17, 2017, 04:41:36 PM »

One pair of phones, or a whole string of them?

if I needed a phones amp, I'd grab me one of those little small mixers, the ones with maybe one or two XLR inputs and a couple line inputs, they are cheap, and have headphones amps in them.

You could also buy a real headphone amp too, but those only do that and nothing else.  My little mixer can be used for many other things that arise.
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ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #26 on: August 18, 2017, 11:52:03 AM »

I think 1-3 phones -

but the impression I am getting is I should talk him out of using the Yamaha as a headphone amp?

I am not totally sure why he is hell bent on that, but seems to me like not a great idea, if not a terrible one.
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Enzo

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #27 on: August 18, 2017, 01:49:38 PM »

Many amps drop main out to phones with a resistor, ther is precedent.  Seems like overkill to me.
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J M Fahey

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #28 on: Today at 02:31:04 AM »

Quote
they had their tech put a 4 ohm 25W resistor in series with the + speaker lead and otherwise just hook it directly into headphones. the headphones they are using are 38 ohms that can handle 1.5W.
Madness.
They need to add a couple 220 or 470 ohm resistors, one in series with each earphone, at *each* headphone out jack.

As is, they will blow earphones, as in catching fire, and kill or gravely damage users.

You must feed *milli* watts to earphones, not full watts (not even 1 W).
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ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #29 on: Today at 02:57:28 AM »

J M,

a 220 or 470 in series with the + lead of each earphone jack or with both the + and - lead of each jack?

what wattage would you recommend for those 220s or 470s? 10? 20? and are you saying instead of the 4 ohm or in addition to?
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