Any help in fixing a JVC JA-11 Amplifier?

[xxxxxxxxxxxxxx]

Hello everyone,
I have recently aquired a JA-S11 Model, JVC brand stereo amplifier. Of course, it doesnt work.

The power supply works and is OK, the power light lights, but there is no click or pop from and speakers on any chanel. There are no other indicator lights.
The unit does not give any output on any chanel when a source, high or low volume, is connected to any input.
Inside, everything is visualy OK, but when the unit is powered up, regardless wheather or not there is an input, the right-chanel amp chip (SanKen S-40W, photo attached) heats up to a moderate-high level, but the other amp chip doesnt warm at all. Remember that neither output works.

No other parts get hot or are obviously damaged pysicaly. There is, however, a small relay which does not seem to be triggering under any circumstances (set by the function switches on the front panel). This relay is a 24v type, and works (tested out-of-circuit), however, the circuitry that triggers it may or may not be functional.

Any suggestions? All help is appreciated (And if you have a service manual that I dont have to pay $20 for, I'd love to know ) By the way, there is no info for what i'm doing on the net (or that i can find).

Thanks everyone

PS: As a side-question, I've attached a diode that has a coloured (yellow) stripe on it. Now i've seen this stuff before but what does this mean (part-wise)? This also appears on SMD diodes. Love to know if you do, thanks again

 

[3v0]

I would think the indicator lights are driven by a uC(microcontroller).
It could be the uC is not getting power or it is toast.
The uC will be a programmed part only made by JVC.

Does the unit respond to any switches that obviously input to the uC.

Hello everyone,
I have recently aquired a JA-S11 Model, JVC brand stereo amplifier. Of course, it doesnt work.

The power supply works and is OK, the power light lights, but there is no click or pop from and speakers on any chanel. There are no other indicator lights.
The unit does not give any output on any chanel when a source, high or low volume, is connected to any input.
Inside, everything is visualy OK, but when the unit is powered up, regardless wheather or not there is an input, the right-chanel amp chip (SanKen S-40W, photo attached) heats up to a moderate-high level, but the other amp chip doesnt warm at all. Remember that neither output works.

No other parts get hot or are obviously damaged pysicaly. There is, however, a small relay which does not seem to be triggering under any circumstances (set by the function switches on the front panel). This relay is a 24v type, and works (tested out-of-circuit), however, the circuitry that triggers it may or may not be functional.

Any suggestions? All help is appreciated (And if you have a service manual that I dont have to pay $20 for, I'd love to know ) By the way, there is no info for what i'm doing on the net (or that i can find).

Thanks everyone

PS: As a side-question, I've attached a diode that has a coloured (yellow) stripe on it. Now i've seen this stuff before but what does this mean (part-wise)? This also appears on SMD diodes. Love to know if you do, thanks again

 

[Nigel Goodwin]

It sounds pretty obvious that one of the output chips is duff - this is putting a standing DC voltage on the speaker output, triggering the protection circuit preventing the speaker relay from switching on.

Download the datasheet for your output chips, and measure the voltage on the output pins, you will find one is zero (the good channel) and the other is high or low (the faulty channel). You may be incredibly lucky and find dry joints on the faulty chip, and resoldering it could cure the problem - but mostly such dry joints kill the chip anyway.

 

[xxxxxxxxxxxxxx]

3v0 - there are no microcontrollers in this amp, its pretty old ('70's). And only one (power) indicator light.

Nigel - I suppose that could be it. Ill have a look after school today, and i'll let you know. Thanks.

 

[rezer]

So it's using TTL chips, in which case the "moderately warm" part could be the good working unit.

Being stereo, I would think that one of your channels should be working if you have a defective amp circuit. It could be something they share in common such as the µP or another part of the system. Can you inject a signal into each individual stage of the input amp to test?

 

[xxxxxxxxxxxxxx]

Rezer - yes i can iterjet a signal, but i will try nigel's idea first. Also, just so you know, this amp has two metal-cased amp chips and one 14 pin Preamp chip. Nothing else but discreete components interesting, really.

Thanks for everyone's suggestions, I will let you know on your suggestions.

 

[Nigel Goodwin]

So it's using TTL chips, in which case the "moderately warm" part could be the good working unit.

Why would an amplifier have TTL chips?.

Being stereo, I would think that one of your channels should be working if you have a defective amp circuit. It could be something they share in common such as the µP or another part of the system. Can you inject a signal into each individual stage of the input amp to test?

Try reading my previous post, which explains why neither channel works - it's an EXTREMELY common fault.

 

[rezer]

Nigel,

That was a "plug" at the age of the unit. Of course, amplifier wouldn't use TTL. Poor attempt at humor, I suppose.

You mention the speaker relay. I'm assuming there are two speakers on his system. Does the relay control both? I probably misread your post. After reading it, I was thinking there were two seperate relays controlled indepenently. I'm not really that familiar with stereo systems. I thought I'de take a stab at it.

 

[Nigel Goodwin]

You mention the speaker relay. I'm assuming there are two speakers on his system. Does the relay control both? I probably misread your post. After reading it, I was thinking there were two seperate relays controlled indepenently. I'm not really that familiar with stereo systems. I thought I'de take a stab at it.

They commonly have one single relay, with two sets of contacts - I've never seen one that uses two relays.

 

[xxxxxxxxxxxxxx]

Thats correct, nigel. It only has one relay controlling two contacts. I cannot find a datasheet for the sanken s-40w, nomatter to my internet trawling. So, I think I will order two S-40W's and replace them both, they're getting old, I suppose, and they're not too expense.

This company (Flytech Electron Co. **broken link removed**) will sell them, new, at $30 ea. I'd like a datasheet, so we'll see what they send back. Not very communicative, it would seem.

 

[xxxxxxxxxxxxxx]

Ok, I have a datasheet for the S-40W/S-60W but I dont understand which pins are the outputs just judging on the internal components.
At the risk of sounding like someone who hasn't done their homework, would someone please have a quick look at the link and let me know what is what. Thanks alot - I have assumptions based on the transistors, but to be sure, to be sure.

The datasheet>> **broken link removed** Thanks!

 

[Nigel Goodwin]

The outputs are the junction of R6 and R7, pin 4 on the first two, and pin 5 on the third.

However, as these are just output darlingtons (rather than complete amplifiers) there could be a fault in the earlier stages as well.

 

[xxxxxxxxxxxxxx]

Ok, well if pin 4 is output on my device, I'll check the voltage at that terminal. With 'earlier stages as well' that means that these are just a component in the amp circuit and there could be a fault someplace else (all discreete transistors diodes etc), right? So I'll check the chips first, then if one is faulty, replace it only, or should I hunt for a cause of failure of the dead chip?

mmm confusing really. I hope it is the chips - that would be easy to do. Thanks Nigel.

 

[Rolf Zetterberg]

A schematic makes life much easier,doesn't it?Register at hifiengine,and you'll get acess to a JA-S11g schematic.

 

[Tim Cadwallader]

JVC JA-S11 Amplifier

I have also just required this model and make of Amplifier, this does not work correctly either.

All the inputs work ,it swithes on,the light comes on and the relay cliks.

I only have sound on the Right speaker nothing on the left can you tell me where I can purchase A S-40W power IC chip to repair this amplifier.

Regards

Tim Cadwallader

 

[xxxxxxxxxxxxxx]

Hi Tim, I never ended up buying the S-40W, I just shelved the project. As far as I am aware (at the time of my initial research in 2008) no-one was manufacturing a new replacement part, but I did find a listing on Ebay for a supposedly genuine new-old-stock S-40W. Various IC resellers in china also claimed to have the part, but did not send me a photograph of it when I requested, so I would be careful here. My suggestion would be Ebay, since they have good buyer protection for counterfeit items. The S-40W was manufactured originally by SanKen Semi.

Hope that helps a little.
-Michael


EDIT: Additionally, as Rolf suggests, HiFiEngine (google it) has a schematic available for free, all you need to do is register. This is what I did.

 

[Mr RB]

Mike you can probably get the amp chip from Wagner in Sydney ph 02 9797 9866, they have a massive range of those amp chips for older amps.

 

[RiddlingCactus]

Hello! I've been following different threads for fixing the JA-S11G amplifier since i got my hand on one my self! I also had the same problem with only sound from one channel(Right) and as i was trying different things i noticed when i turned the balance all the way to the left i could hear a slight sound coming from the left channel, in my case this had to do with the "Monitor Switch" on the front panel, it has some kind of bad connection so when i worked it slightly up and down the sound would suddenly appear, and suddenly it was gone again. I would also think some of the others switches can have some malfunction/bad connection which causes problem with the output signal to the speaker relay on the back. Either way, this was after i replaced the two Darlington Power Packs(STK-0040, from Ebay) since the 24v- DC relay wouldn't switch over, and that would be the easiest way to try fix it, and it worked!!(shipping costs was over the actual price of the two Darlingtons), and then the next problem was sound coming only on one channel which in my case is the front panel switches, caused by being stored outside summer/winter(i would think?) for over almost 15 years! I hope this helps, it worked for me...

Edit: i used something called "Electronic cleaner", i just unscrewed the front panel, pushed the "clothing piece" aside and then applied some cleaning fluid as i rapidly pushed the switch up/down several times, i did this a couple of times and it's working much better but still the connection sometimes break, it may be possible to mod the switch in someway? With the help from a data sheet/schematic or something, or with the proper knowledge, i am not an engineer but it shouldn't be that big of a problem..

 

[DPeter]

I found it very interesting that two of you describe sound from the right channel, and just barely perceptible sound from the left, because that is exactly what I have in my JVC SA-S11 amp!
So I followed RiddlingCactus's lead and simply cleaned all the pots and switches on the front panel with electronic spray cleaner and everything is working again!!!!
Wow, that amp had not been fired up since the early 1980's!!
Just thought I should add my experience to all of yours. I am amazed and happy. Thank you for your help!

 

[yosef Azab]

I got my father’s old JVC JA-S11 it was in storage for over 15 years.
When i first turned it on only the right speaker was working so i applied electronic cleaner in the knobs and switches , and the left speaker worked but with a lot of noise so i thought it just needed cleaning so I disassembled the device and gave it a good cleaning.
Unfortunately now whenever i turn the device on the light goes on but without the click and nor the left or right speaker work.