ZOOM 9030 malfunction

Owned from new and carefully looked after, this ZOOM 9030 began to give trouble around 2010. I switched on one day and heard a quiet hum through the headphones. I made some recordings via the stereo amp outputs and from memory these were hum-free, so I put it down to faulty capacitor in the headphone circuit. I thought it was likely a very minor fault and provided it didn't interfere with actual recordings I wasn't too concerned.

As time went on, the drive module began to malfunction. The overdrive or distortion would be abrupt and very harsh. Usually switching the unit off, then back on would cure it. More recently this became a regular annoyance so I would just leave it and use other equipment instead. The thing was, I missed the analogue overdrive, SFX and generally brighter sound of the Zoom.

At times the overdrive would disappear completely, and then the compressor began to cut off. Something seemed to be causing a rapid decline, so I thought it was time to have a look inside. I had never needed to take off the cover - not even to change the memory battery. I am far from being an expert in electronics but I thought maybe there was something I could do.

Sliding off the top cover, I saw a bundle of wires jammed down the side of the chassis. Victim of rushed assembly ? Had the insulation been damaged ?

Not good. But the insulation was intact.

Looking inside I first checked the analogue board. I could see corrosion around the pins of OP10. In particular, the pin 4 track had been savagely attacked by something - there wasn't really much of it left by comparison with the others. The reason is electrolytic corrosion. Electrolyte from a leaking capacitor is corrosive by itself, but made much worse by current flow on a wet board.

Leaking capacitor. Which one - or maybe several ? I cleaned up the area.

I did a search online and found a discussion about a ZOOM 9030's failing compressor on the German Sequencer site. It was mentioned that C99 had leaked. Looking at my board, there was fluid nearby C99, C98 and a row of soldered connections. This fluid seemed fresh whereas the fluid around OP10 must have dried some time ago.

It was likely that all these SMD capacitors would need to be replaced. I have never worked on SMD boards and wasn't relishing the prospect. 2 plugs connect to the top of the circuit and I used fingernails on the small lip to separate them. This took some patience !

It wasn't clear how this board lifted out of the chassis - there were 2 phillips screws along the edge, but the board still seemed firmly attached. It turns out that there are 2 multipin plugs on the underside which connect with the main board.

I lifted the board with one hand and carefully positioned a small flat screwdriver through the chassis opening where the bundle of wires had been poking out. This pushed up the board near the front mounting hole which is convenient because the smaller of the connecting plugs is in this area - this meant the lifting force was spread out more evenly.

Next step is to note all the cap values, remove them and clean the board of the leaked electrolyte.

I don't have an SMD hot air blower and the solder pads were hidden under the plastic base of each cap. Some people grap the cap with pliers and repeatedly twist to break the connections inside but this has a risk of damaging the solder pads. I used a very sharp, small pair of end nippers and cut about halfway up the can. My idea is that the connection between capacitor and pin will be severed cleanly and rough twisting to fatigue the connection will not be needed.

This seemed to work, although I still had to make repeated very small twists to free each can making sure not to pull vertically.

The cutters need to be very sharp (I ground mine on a stone). Even with sharp cutters the cans distorted so I carefully reshaped the remaining part of the can back to a circle. My cutters had parallel edges so that no side forces were applied to the solder pads (which would happen with diagonal side cutters).

I cut in line with the polarity markings. The reason for this is that it does not distort the pins that come up from the board.

Cans removed but some capacitor seals are still in place. I made a cut in some of the seals with a scalpel and lifted them out.

The capacitor's aluminium sleeves are attached to the pins which are soldered to the pads. I didn't know this before cutting open the can - I feel happier about cutting since I haven't stressed the pads, but as those aluminium sleeves are not going to just slide off I will have to trim them. All solder pads will need to be checked for corrosion.

The picture above shows the remains of C6 which was difficult to cut due to being so close to IC1.