Genelec 1031 Driver cards need repair/help

[Nele]

I have a weird issue.
I've been asked to install four of these boards into two monitors (1031A). Both treble and bass. The treble boards didn't fit because some components on the main board were in the way so some resistors are mounted on the other side. I didn't solder the boards btw.

I put in the boards and tried to calibrate them. This is where it got weird. The treble board calibrated fine and was stable, the bass board gave me -52V on the output. As it was soldered onto the main board I desoldered it and put in a socket so I could swap the remaining boards. When I put in a treble board it was stable and I could calibrate it. When I put in the other bass-board I got 52V on the output.

So: the two treble boards with resistors on the back are working ok, the two bass boards (components all on one side) have problems.
After checking everything and replacing a broken resistor both boards are kind of functioning but I can't get the output to 0V. They slowly drift upwards end sit around + 250mV... Any idea what's going on and where to look?

 

[saint gillis]

I have a weird issue.
I've been asked to install four of these boards into two monitors (1031A). Both treble and bass. The treble boards didn't fit because some components on the main board were in the way so some resistors are mounted on the other side. I didn't solder the boards btw.

I put in the boards and tried to calibrate them. This is where it got weird. The treble board calibrated fine and was stable, the bass board gave me -52V on the output. As it was soldered onto the main board I desoldered it and put in a socket so I could swap the remaining boards. When I put in a treble board it was stable and I could calibrate it. When I put in the other bass-board I got 52V on the output.

So: the two treble boards with resistors on the back are working ok, the two bass boards (components all on one side) have problems.
After checking everything and replacing a broken resistor both boards are kind of functioning but I can't get the output to 0V. They slowly drift upwards end sit around + 250mV... Any idea what's going on and where to look?

Do you have pictures? which resistor was broken?

 

[Nele]

One of the 5K6 resistors was broken. Will post pictures later today..

 

[Nele]

Ahum, I meant later next month...

 

[saint gillis]

The board was made for smaller resistors, of course it's not a pbm, but are you sure there are no leads touching each other?
Also these round marks on the pcb indicate where to put the body of the component for the ones placed vertically :

this should help to prevent leads touching each other

If you have not assembled the boards yourself maybe there are mistakes? check the components values, diodes directions, etc..

 

[Nele]

Thanks. No, I didn't assemble the boards. The owner asked me to install them and calibrate the monitors. That's where the problems started. The weird thing is that he assembled four boards, two with some resistors mounted on the reverse which work fine (not pictured), from the same batch of parts.

 

[Nele]

Leads are not touching. I noticed that not all solderjoint were soldered 'through' but they do measure ok and the holes are through-plated...

 

[saint gillis]

After checking everything and replacing a broken resistor both boards are kind of functioning but I can't get the output to 0V. They slowly drift upwards end sit around + 250mV... Any idea what's going on and where to look?

Is the 250mV offset still related to the PA driver ?
If you swap the cards, is the problem still related to the cards you fixed ?

 

[Nele]

To clarify: the owner soldered four driverboards. He then noticed that the treble boards wouldn't fit because some components were in the way so he soldered some of the resistors on the other side.
Oddly enough these changed boards are stable and I am able to calibrate the monitor per the servicemanual.
The other two boards, with the resistors mounted as intended, are unstable. If I swap the boards the offset starts drifting and it's impossible to tune them.
So yes, it's related to the drivers.

 

[saint gillis]

Maybe it didn't fit because he used 6mm resistors instead of 3mm..

I would check the 5V1 zeners, not the 2 at the top-right corner, the 2 others..

 

[saint gillis]

Then the 27K resistors next to them, and the two 3K9 ..