Repairs required for Audiolab MDAC Power daughterboard

[Desmo67]

I got my hands on another spares or repair original MDAC last week and have just started looking at it. The main board looks ok - no obvious signs of damage.
I get the feeling someone has tried to replace the 5 large Capacitors (none present but they should be 4700 uf I think) on the Power supply daughter board.
The mid capacitor looks to have overheated (scorch marks on the board) and bled its electrolyte. It also looks as though the interconnections through the board have been damaged - the pads around the holes have lifted and it looks like connections from them, through the holes have snapped. Two of the nearby resistors have also come free (these were included in a plastic bag).
I'm wondering how many layers are there to the PCB and on which capacitor legs are the connectors passing through i.e, is the negative connecting to the track on the top layer and the positive to the bottom layer, for example, and where are the top and bottom layers connected.
Is there a way to repair this - or did I waste my money ?

 

[mjwin]

If your Audiolab MDAC is anything like my 8200CDQ (CD player/ DAC / preamp) it uses a load of paralleled Lelon capacitors crammed together next to the regulator heatsinks. Just by chance I happened to notice that the capacitors in the first stage filter were swelling, but managed to catch them before most of them had ruptured. My unit has been powered up almost continuously for about 7 years, but it's the temperature which kills them. I replaced mine with Wurth 105degree equivalents (the most immediately available types in 16mm diameter cases).

As for the board, I did find the soldering quite difficult. It's probably a 4 layer board, but seems as if there aren't any thermal reliefs around the ground plane pads. I didn't hold it up to a bright light to confirm this, and the Pb-free solder is harder to remove, anyway. But with the aid of a solder sucker and some gentle persuasion, I managed to make a clean job of the replacement. I would imagine that the MDAC pcb is similar. But you do need a high powered soldering iron (50W) to manage this, and the previous owner might have resorted to bf&i (brute-force-and-ignorance) as is often the case!

I'm sure your unit can be repaired, so don't give up! Generally, the through plating is quite substantial, even if the surface pads are lifted. Can you do some continuity tests to check? BTW, the circuit diagram is probably available online somewhere, mine was, but I forget where. Provided you can clean out the holes in order to insert new components, you should be ok.

 

[nimar]

Out of curiosity what does an m-dac for parts cost? I've a perfectly working m-dac on a shelf, but it has a UK (220) power supply, which since moving to Canada is less useful. I did buy a rather large transformer to use with it but its rather cumbersome and unsightly which is why it ended up on a shelf. Have been considering selling it, but due to the power supply suspect there will be little interest on this side of the pond.

I briefly looked at buying a 120 power supply for it but did't know exactly what I needed.