RAM Batteries - Oberheim DMX

• To retain synthesizer memory, needed to replace RAM battery - was a bitch to find
• 1x button not working due to spring contact, attempted to resolve via a piece of plastic to elevate the contact so there's more room for the spring to move - fixed
• fun machine

Linear Power Supply

From left to right i.e. AC 220V to DC 15V in this example:

1. Incoming AC Voltage goes through to primary coil of transformer
   • #transformers work via creating electromagnetic field to step down incoming voltage to desired voltage
2. A: With Electromagnetic flux, AC voltage is stepped down to 20V
3. B: A set of diodes determine the polarity of the power output, forcing positively-fluctuating voltage
4. C: A set of capacitors smooths out the voltage fluctuations and raises the starting voltage
5. D: A regulator steps down the voltage further via releasing heat
   AC vs DC

Transformer coil formulae

V_s = T_s / T_p x V_p
where V_s is the voltage at secondary coil, V_p is the voltage at primary coil
T_s is the number of coils at secondary and T_p is the number of coils at primary

what a transformer looks like in real life

Fuses

have slow timed blows or instant blow types

• current rating: current at which fuse will blow
• voltage rating: if the fuse blows at this voltage, no sparks are guaranteed

Boss PQ-4 #Pedal Repair

Initial issues:

• can power on but no sound
• bypass switch works, led turns on and off

After dismantling and mild investigation via the schematic, found that the input and output jack connections were corroded. Resolved by replacing new input and output jacks with new single-core wires