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Jungson J88 Intergrated amp


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First up. People keep asking me.

Is it really an 80w class A amp ?

Someone else has done the calculations and they believe it is more likely 10w class A into 8 Ohms.

 

Now. Fault. Not working one channel.

Discovery. One amp of four not working.

 

No yes, it's a two channel amp, but each channel uses two amps bridged. One positive and one negative per channel. (See schematic at bottom).

 

post-106429-0-04864700-1464072145_thumb.

 

Do NOT be fooled by the rear panel marking. It is NOT earthed. Legally I think Jungson should cop an earfull and a huge fine for this. HA. Like the chinese would care.

 

post-106429-0-85120500-1464072157_thumb.

 

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Now the comes the horror of pulling it apart to fix it..... (Hindsight I should have stopped here and slit my wrists)

Remove screws, Cut cable ties, 'Hinge' open back panel.

 

post-106429-0-15716600-1464072222_thumb.

 

Unsolder three wires either side.

 

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Allows back panel etc to open enough to get at the 6 screws holding the internal back board.

Then you can remove various other screws holding support braces and panels. 

 

post-106429-0-61022400-1464072298_thumb.

 

Unbolt the heatsink/amp assembly, and persuade the lot to come free of the case.

 

post-106429-0-33629700-1464072333_thumb.

 

Um, yeah, ok so 'free' is an subjective word here. Everything is connected with soldered wires running everywhere you can't reach.

 

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To get to this point.

Use a 1/4" socket set and 7mm spanner to undo one side of the output transistor clamps till there loose enough to 'persuade' the heatsink to separate from the output transistors.

Are we having fun yet ? - No.

 

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Take note of the two grey wires in the middle joining the transistors middle pins.

 

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To add to the fun a wire broke.

Thought I'd better fix it. Errrrrrrr, were they expecting to use a somewhat bigger cable ???

Yes, that tiny wire, goes in that huge hole. HEY, I heard that sniggering. Stop it now !

 

post-106429-0-99881400-1464072414_thumb.

 

 

Right. Almost half way.

Amp is exposed and in a serviceable (sorta) condition.

Fault is found and rectified.

All parts have been checked and tested by multimeter - Several times (you'll see why shortly)

Now for the fun part, Putting it back together.

No. It will never go back together the way it came apart. *Runs off sobbing in the back ground.*

 

Remember these two wires ?

They have come out.

Why ?

Because they are soldered directly to the middle pins on four of the output transistors.

ALL of the output transistors have to come out for reassembly.

 

post-106429-0-57045000-1464072431_thumb.

 

So we put in two new wires in a slightly different position that won't drive me over the edge.

 

post-106429-0-70516800-1464072442_thumb.

 

Yup. All eight transistors, removed. Then clean out all the solder from the board. Then clean the board. And clean up the transistor legs.

 

post-106429-0-77483300-1464072461_thumb.

 

More fun.

Measure and mark out where the transistors will go back into the heatsink. Grease / clamp / measure / tighten. x 8. Oh, and recheck all 8 for correct static function and shorts to the heatsink.

 

post-106429-0-93217500-1464072481_thumb.

 

Not shown.

Carefully guiding the heatsink assembly with 24 transistor legs back into the amp board.

While the board is still tethered to the chassis, cause, we like to hide wires and make them impossible to get at for service work.

I should've just reinvented the universe. Would've been easier.

After getting heatsink assembly back in touch with the amp board, you have to heat flow solder from one side of the board, through to the other side, that can't be gotten at once the heatsink is in place.

Ahhhhhhhhh now you see why I had to reroute those two wires and remove all the outputs.....

 

 

What that ? 

Nooo you don't really want to know what the actual cause of the fault was do you ?

Sigh. Oh alright.

Drum roll please . . . . . . . . . Ladies and gentlemen. I give you the reason I spent over a week bench time on one repair.

 

 

 

 

post-106429-0-22931600-1464072121_thumb.

 

Yeah. Thats right. One single frikken resistor. Open circuit.

That and the nightmare to reassemble that I could see coming is why I went over every component 4 times to make sure that was the only fault.

 

And this is where the bugger lives (red circle).

 

post-106429-0-72196900-1464072498_thumb.

 

In closing. There was just absolutely no way in any universe this resistor could be replaced without the strip down.

The whole amp is just so tight for space.

I have seen photos of the same model with pcb connectors. Must be later/earlier revisions.

Would've made life, no, actually it wouldn't helped much at all.

Still would've had the fun of stripping out the outputs and reinventing the wheel.

 

This, This makes two brands I will never, ever, touch, ever again, in the rest of my life.

Seriously. No amount of money or first borns will convince me otherwise.

 

 

 

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Jungson?

 

*looks for barf smiley *

 

LOL.

 

 

Cheers!

Drink up now!

You need one I bet!

 

Seeing it being carried out the door will do.

Not allowed to drink (doesn't always stop me though) Type 2 diabetes.

 

Was it as painful as the Classe? Looks time consuming.

 

I would say worse.

At least the classe you could pull apart to work on without as much drama.

 

And how does it sound?

 

Only ran it on the bench into test speakers.

Seems to do what it should.

 

My next trick is to create life from thin air.

 

Um, thats making a Nelson Pass M2 amp from many boxes containing many bits.

Started that this arv.

 

Oh the freedom of a simple clean design with heaps of room and ease of any future servicing needs......... :love

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Better man than I.

 

 

Who says I'm a man ?

Nah, I is :D

Maybe I'm just a little more loopy than most ;)

 

 

Wow I dunno what was going on still it was an entertaining read. Well done!

Sent from my iPad using Tapatalk

 

 

Baffle with B.S.

Dazzle with incomprehensible mumbo jumbo.

Be the life of the party by leaving the others confused with no idea why their confused.....

 

Maybe I should run for PM.

 

:D

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Jungson JA-88D — full model name added so hopefully other owners can find this thread when searching with Google. It's great that you've got a schematic, I couldn't find one when I was looking.

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The designers should be taken out and S**t

What a nightmare

Do you think that the original builders/ assemblers had tiny hands ?

I believe the original designer has passed away.

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A good read. I owned one of those models for a year or so, and was very impressed by the sound quality outputted of this huge beast.

 

Luckily mine worked as it should have, although they do get very hot in operation.

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From a technical perspective, I've had to rebuild a LE 88 and 99 and while they sound decent, look quite nice screaming high end (like most Chinese gear) they are horribly designed and constructed. As Green Wagon as shown the way they mount the output devices to the PCB's secured to the heatsink is very non-economical for repairs making it a PITA. Most of the output and driver stage devices are soldered directly to the PCB which the solder pads comes off after a few desolder (use 250'C on the iron here). Another problem with the LE 88 and even the 100 is that there is a problem with the relay circuitry and one or two resistors do go faulty over use (can't remember which one) and the relay gets stuck or constantly engage and dis-engages itself when the amplifier is on.

 

There are at least 5 PCB versions of the 88 that I have been told and seen. You think Jungson is bad? Try fixing some of the Doge preamp and amplifiers, poor circuit design decisions, poor quality parts and poor design and construction.

 

Like the old Unison Research stuff, you have disassemble half the amplifier to get to components that most likely to blow or go faulty.

Edited by liteneasy
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From a technical perspective, I've had to rebuild a LE 88 and 99 and while they sound decent, look quite nice screaming high end (like most Chinese gear) they are horribly designed and constructed. As Green Wagon as shown the way they mount the output devices to the PCB's secured to the heatsink is very non-economical for repairs making it a PITA. Most of the output and driver stage devices are soldered directly to the PCB which the solder pads comes off after a few desolder (use 250'C on the iron here). Another problem with the LE 88 and even the 100 is that there is a problem with the relay circuitry and one or two resistors do go faulty over use (can't remember which one) and the relay gets stuck or constantly engage and dis-engages itself when the amplifier is on.

 

There are at least 5 PCB versions of the 88 that I have been told and seen. You think Jungson is bad? Try fixing some of the Doge preamp and amplifiers, poor circuit design decisions, poor quality parts and poor design and construction.

 

Like the old Unison Research stuff, you have disassemble half the amplifier to get to components that most likely to blow or go faulty.

 

It's jobs like these that make you sit back and think, Do I really want to be doing repairs.

Then you get a nice couple that fall together and you forget the pain.

 

Re pcb issues, yeah that's one of the reasons I won't go back into this amp. After doing the solder flow through, the fiberglass substrate gives you that distressed look where you just know it won't take much more to fall apart.

And I agree with every thing you said.

The potential is there. Just screwed over by cost cutting and stupid design choices.

Its a shame, cause from outside it looks really really nice.

 

 

They probably made him service his own amps ;)

 

Oh how I wish that was possible.

But if you read the little bit of small text from the first link.

The designer was a dentist (Grrr just went a dentist today. End bill will be 2k. I'm in the wrong business)

He then sold licenses to build his circuit design to whomever would buy it.

Thats where it falls apart.

Not so much the circuit design, but the people that then use cheap parts, cheap labour, and mash it together for pure profit.

Edited by Green Wagon
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Dem be solid copper.

Thinnish copper plates, separated by cooper blocks, then thick copper plates for the transistors to mount too.

All held together with threaded rod down the guts and a nut either end.

 

I'd say it has some anodizing on it as well as trying to get a dmm reading across it requires 'puncturing' the coating.

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That is thermal paste for you. Can easily be cleaned off with thermal paste remover or 100% grade IPA. Mica pads are mostly used to isolate the Collector from grounding to the heatsink and is supposed to be used with a small bit of thermal paste. Silicon pads are OK but can disintegrate over time (the ones I've seen in amplifiers in bad storage conditions) or rip apart.

Edited by liteneasy
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all that messy white silicone grease (get's bloody everywhere, ever tried to wash it off your hands, almost impossible!) and mica pads on the output semiconductors could be replaced with Sil Pads

eg,

http://www.bergquistcompany.com/thermal_materials/sil-pad.htm

 

Normally yes, but in this case the grease helps to hold the insulator and transistor in place while I tightened the clamps.

 

That is thermal paste for you. Can easily be cleaned off with thermal paste remover or 100% grade IPA. Mica pads are mostly used to isolate the Collector from grounding to the heatsink and is supposed to be used with a small bit of thermal paste. Silicon pads are OK but can disintegrate over time (the ones I've seen in amplifiers in bad storage conditions) or rip apart.

 

Theres a HUGE thread on diyaudio about mica/goop/silpads/alu oxide/be oxide et all.

Including some that 'split' mica washers into thinner sheets.

 

On my builds what's recommended for transistor connection to the heatsink is Kerafol Keratherm Red transistor insulators

 

Yup. One of the few that is regarded as better than mica and goop.

It's nice to use to as one side is that tiniest bit tacky so it will stay where you put it where as silpads are dry and can move around a bit. That can be a pain.

 

 

 

Hell I even remember a test maybe a decade by a computer magazine (Atomic) comparing a lot of the 'ultra' goops.

Arctic silver, normal silicon paste, can't remember the rest, but they even tried peanut butter. did surprisingly well but wasn't recommended for long term use.

Biggest issue is using too much. Only needs to be a thin smear to fill ridges in the surfaces.

 

What I like to do (and did here) is clamp the transistors, test for punch through, let it sit overnight for it to settle down and stabilize, then test it for punch through again.

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