Some photos showing the effect of oxidisation (green residue) on the metal edges of components as a result of the memory/settings backup battery that is PCB mounted. The battery is an RS Components catalogue number 422-371, which is a rebranded Mempac 2.4V, 110mAh Ni-MH cell.
Removal of the existing battery exposed some more of the damage from the corrosion – notably track damage around the holes where the battery legs were.
The area was cleaned up using a fibreglass abrasive pencil and IPA. Any peeling tracks were also tested for continuity from the components they connected to.
A new replacement battery was ordered and installed. One of the existing holes that also suffered track damage was actually not connected to anything, so was safely omitted during soldering. The battery was stabilised with hot melt glue to prevent any flex or pivoting from detaching the damaged track.
My nephew’s Rockjam keyboard came back with me after we did a sponsored walk together. The keyboard takes a 10V DC wall-wart power supply, and was exhibiting signs of hiss and hum. I initially checked that it wasn’t a failure of the power supply’s rectification by attempting to run it using another supply – the problem was still present.
Opening it up, I can see from the main board that there are two electrolytic capacitors that had pinhole ruptures on their tops.
These were 470µF/16V and 1000µF/25V. The latter appeared to be a smoothing capacitor, operating in a pair. All three were replaced with electrolytic capacitors of the same value, but higher voltage rating to improve longevity.
Upon powering up afterwards, the idle on the keyboard was practically silent.
The BOSS OS-2 is a pedal designed to give the player a combined set of SD-1 and DS-1 tones in a single robust box. I managed to buy this one reasonably locally on the basis that the ‘Color’ and ‘Drive’ controls had snapped shafts. Whilst made in Taiwan, this one was still slightly older than the current generation one – consequently, it used potentiometers that had 16mm metal backshells and 5mm pin spacing, but the tapers and values aren’t as commonly available as others.
There aren’t an abudance of authorised Roland/BOSS parts dealers around, but I was able to contact the nearest authorised repair specialist.
They were extremely kind in being able to provide the official schematic for the parts (not that I needed it in this example, as the potentiometer resistance values and tapers were marked on the remaining parts), but more importantly, they were also able to order the parts on behalf of me, from BOSS in Japan.
Parts arrived a few weeks later, at £20 for the pair of potentiometers all-in.
But there was a problem…
…They had supplied the potentiometers for the more modern version of the pedal – I’m assuming due to the original sized potentiometers now being obsolete.
As the shaft size, type and threaded area was correct for the pedal, I pretty much had to go with these. So I had to use solid core hookup wire, cut it down to approximately an inch and a half in length, use forceps to bend small loops at the end and then solder it to the legs of the potentiometers.
The two main challenges I faced were 1) Leg spacing and 2) Heat transfer. The former to avoid accidentally soldering legs together, given the added space occupied by the looped wire and the latter to avoid melting the internals of the plastic boded potentiometer. I was using a conventionally sized soldering iron with a conventionally sized tip, which in hindsight, added to the challenge.
It wasn’t pretty, but it worked.
Putting it all back together, I now had my OS-2 work “good as new”.
One of the most annoying things to deal with is when the tip of an instrument lead plug decides to break off and lodge itself inside the socket.
The reason this is annoying is that it is such a simple problem, but often cannot be recitified without opening up the amplifier to gain access from the top of the jack socket. If you get lucky, sometimes you can use a spike or a skewer and raise the socket pins enough for the offending part to drop out.
It’s worth suspecting this situation when you observe:-
A cable refuses to be fully plugged into a socket and
The amp is (nearly) silent
Much of the time, to avoid damage to the relatively thin metals of the socket innards, a good set of steel picks is a useful tool to have.
I’ve been trying to locate the cause of blocking distortion on a friend’s Line 6 Flextone 3 XL combo. Characteristics of the problem are: on low signal levels, the sound decays and gets “chopped off”, similar but not as neatly as a noise gate would work, whilst high signal levels (for example, hard strumming on the guitar) would sound fine.
On the Line 6 Flextone 3, the input jack socket is mounted on the chassis and has a preamp circuit on a PCB. Firstly, the jack socket itself should be checked for good conduction – if it appears excessively tarnished or oxidised, it’s worth replacing it.
Secondly, the input socket PCB assembly is connected to the main board via a cable with Molex style push connectors. A bad connection in the connector can cause the blocking distortion problem.
Where the input socket PCB connects to the main board.
Clean both connector parts, with something like an interdental toothbrush and some metal polish – not forgetting to clear out the residue with either rubbing alcohol or contact cleaner – and then secure the connector either with hot melt glue or silicone. This has worked for me, resulting in a crystal clear input signal once more.
This USA made 50W RMS twin combo arrived with me, needing dusting and a more permanent fix to the ‘rats tails’ and speaker tab. Nonetheless, the insides still look relatively healthy, without any evidence of heat related damage nor leaking electrolytic capacitors.
Speakers are 12″ Eminence made Crate labelled drivers.
Of Sound Mind 