Genelec 1031a amp gone crappie

One of my genelec 1031a amp is making a noise like a hum or buzz. 
I have replaced the filter caps  for the 57 volt  and the 15 volt supply.  I have also sprayed contact cleaner on all connectors.  No Love.

there is a ribbon cable going from the power PC board to the input PC board and I have found that if the input board is plugged in the 15 volt rail get pulled down to about 3 volts.  if its unplugged it stays around 15VDC.

This amp uses the STK 4241V amp IC.

Any help would be great.

thanks
fvf

there is a ribbon cable going from the power PC board to the input PC board and I have found that if the input board is plugged in the 15 volt rail get pulled down to about 3 volts.  if its unplugged it stays around 15VDC.

Click to expand...

i think it can be assumed that there´s something going on on the input pcb
you got the schematics ?
what is the input pcb doing ? ( i´m guessing preamp , crossover ? )
are the IC´s on sockets ? if so you could try pulling them one after  another to see when the voltage drops .
You might be able to narrow down the area with the fault .

this all just guesswork , though .
i never had to repair this  particular speaker nor did i look at the service manual

Thank you for the reply.

Genelec won't give out scem. 

The input PC is all smd.  It is mostly 5532, res., and caps. As one would think. 

I have one good one and was thinking of trying it input board to verife. 

The only other thing is the input board goes back to the power board where the STK 4241v is also located so maybe a bad amp IC. 

I'm at a loss as how to test for this.

Thanks
Fvf

The service manual for the 1031-a can be found here:

https://groupdiy.com/index.php?topic=46298.0

It's listed as "1031", but it's for the 1031a. There's a couple of opamps on the input board and an opto for the remote volume control.

Thank you for the link.  I had downloaded it but the layout is different from my amp.  I was able to get voltage and some pinouts.

I will include pictures so you might get an idea.

thank you

fvf

the input board

the overview of the amp.

the power board

Your input board seems to have 5532's. The schematic has TL072's.

I had a second service manual. Different source,  different name, exact same content. Sorry.

Does any of those 5532's get hot?

it all good.  Nothing gets hot or looks bad. 


Genelec will repair but shipping cost and 100.00 to look and then cost of repair.  if it the amp chip is bad the service guy said it could be 500.00.

my guess is to take my good input board and swap it out so if the amp is good, it's the input board,    if bad it's likely the amp IC.

I got a new old stock STK 4241v from a store so if the amp is bad I might try the repair myself.

just don't want to put 500 into a speaker that is 20 years old. 

thanks
fvf

Can you post the clearest possible picture of the board that is failing? I mean the one that is causing the other board to drop from +15 to +3. You're starting off well by jigging. Divide and conquer. What voltages do and don't match from the one speaker to the other? Can you remove parts until the issue stops? 

So, Were both speakers working at some point?

You changed the power supply caps because of the problem? did you change the power supply caps in both???

I'm not sure I'd swap  boards assuming any other board is not goofy...

It does sound like it's dropping power into something that's not working right.... without testing other components, I wouldn't want to just throw a new ic in there...... There are not that may parts in there.....can't you test for faulty components ???? a bad resistor???etc.....

I think testing/comparing voltages from a working unit sounds safe enough if you are careful and mind the orientation of your probes and where you put them. You can easily damage the working unit with one wrong slip....

Please Keep us updated...I'm curious too....

Hi all

If you look up the thread you will see my posted pictures. The one that is the input board is what pulls down the voltage.  The is only the ribbon to wiggle.  SMD the lot.

I have not touched the good speaker.  This started with me leaving the speakers on and coming back from the restroom to find one speaker making a bad noise.

As far as reading voltages as soon as I have the input board plugged in the 15 voltage  on the  plus and minus pulls down clear back to the bridge rectifer.  It's like something is bussing to ground. 
I wonder if the 15 volts goes to the input board first and then comes back to the amp IC. 

If I knew more I would lift the amp IC of the 15 volts and see if the power still pulls down.

I will let you all know.

Thanks
Fvf

The power supply seems to survive having a suspect board plugged into it, so I'd borrow the power supply from the good speaker and try it with the suspect board. That will narrow down the fault to PSU or board

Nick Froome

ffarrell said:

Hi all

If you look up the thread you will see my posted pictures. The one that is the input board is what pulls down the voltage.  The is only the ribbon to wiggle.  SMD the lot.

I have not touched the good speaker.  This started with me leaving the speakers on and coming back from the restroom to find one speaker making a bad noise.

As far as reading voltages as soon as I have the input board plugged in the 15 voltage  on the  plus and minus pulls down clear back to the bridge rectifer.  It's like something is bussing to ground. 
I wonder if the 15 volts goes to the input board first and then comes back to the amp IC. 

If I knew more I would lift the amp IC of the 15 volts and see if the power still pulls down.

I will let you all know.

Thanks
Fvf

Click to expand...

absolutely no need to try with the boards from the other working speaker.
just use a dummy load to draw some current from the +/-15V supply rails, and check if they also drop down to 3V.
if they do, you have a faulty power supply. if they don't, you have a bad input amp board.

The service manual listed earlier has some good operational info. . Although not the same boards, I'd guess the theory of operation can't be too much different??

Just a guess: I just fixed my 1030, it had a 'broken' solder joint at a Molex connector. Un- and resoldering it did the trick. Of course I have no idea whether yours has a similar problem, but it might be worth a closer look in case you haven't anyway done that already.

Michael

Thank you,  I did resolder all the connectors with hope of an easy fix.  No luck.

But I did get a chance to exchange my working input board for the one in the bad amp and it fixed the problem.  To be sure I put the supect input board in the good amp and it made the same crappy sound.  So I know it's the input board. 

The problem is the whole board is SMD and I'm not the best at repairing those.  I plan to call Genelec to see if I can just exchange my board for a good one. 

The input board has seven 5532 op amps and my guess is one of them took a dump.


Any how just wanted to update you all.

Thanks for your help.
Fvf

Have you checked for shorted pins on all the input board ic's? Check the diodes (V105s).

It might just be shadows but these's a few dark patches around a few components, could be burn marks from failure?
I'd get the faulty and working board side by side and just poke about comparing values with your mulitmeter diode check function. (powered off)

If some of those smaller brown ceramic capacitors are across the supply rails, and one's gone short-circuit internally, that may well be the culprit. I've revived several laptops that had shorted ceramic caps, as well as one of my Tannoy Precision 6D monitors.

Not sure if (even) the component designators are the same between your revision of the input board and the one in the service manual are the same, but i'm referring to C420/421 on page 30.

Assuming you have a multimeter with a continuity beeper, you could "hunt" for the ceramics that are on the +/-15v rails of the opamp supplies. One probe on the +15v pin of that 10-pin ribbon connector (maybe solder on a wire and connect an alligator-clip), and try both ends of all the small brown ceramic caps you can see. Repeat with one probe on the -15v pin. Once you've determined which ones they are, you can probe across them to see whether they're internally shorted or not.

Are there any components on the back / bottom side of the input board?