repairs to guitar amplifiers & hifi amps

 REPAIR CHARGES

• Testing prices range from £50 - £100 and often fault diagnosis is part of the initial tests. 

• The testing fee is deducted from the final charge if the job goes ahead.

• In most jobs a deposit is required, all work is guaranteed, and service reports given upon request

The main issues that affect repair are design faults, long term use and/or abuse, environmental conditions of the location where the equipment has been stored (i.e. condensation for instance) and equipment which has been quickly and badly repaired or modified.

REPAIR PROCESS

• Fault diagnosis: visual inspection, AC/DC measurements, signal tests, component tests

• Remedy : Replacing faulty components, cleaning and tidying up

• Testing : At full capacity plus necessary adjustments i.e. biasing in output stages, repeated soak tests etc

VALVE AMPS

There are factors to be considered when restoring and repairing a valve amp which has been used a lot over the years. Pubs, recording and rehearsal studios can be hot and humid places. The amps get hot during use and then cold when they're left in a car overnight, they also run on dangerously high voltages. Safety must be taken very seriously. There are also design faults associated with modern tube amps.

Sometimes amplifier repair is complicated due to intermittent and knock on effect problems. Therefore thinking time is needed, especially with design faults where modification might be necessary. Old used amps may require restoration work.

SOLID STATE AMPS

A schematic diagram is nearly always  needed for quicker fault diagnosis because  transistor circuits are more electronically complicated and sometimes it takes longer to find the fault. However, serious design faults that affect reliability are rare in solid state amps because unlike valves, transistors fail as soon as their maximum power/voltage/current  ratings are exceeded.

Generally speaking deterioration of materials (except Printed Circuit Boards i.e. PCBs), in old solid state amps is not as severe (as in valve  equipment) because most of the circuitry operates at lower voltages and temperatures. PCBs however, particularly PCB traces in locations where hot components are mounted, do deteriorate badly in solid state amps too.    

Where catastrophic faults have taken place in output stages however, full PCB reconstruction and rewiring will be necessary. Due to printed circuit board design, in most cases, solid state (and sometimes valve) modern amps must be completely dismantled in order to replace one or two components.

Problems are more unpredictable in transistor equipment and in output stages knock on effect, catastrophic faults are often seen. There is more diversity in solid state design than in tube circuits. Full restoration may not be necessary in old transistor equipment provided the safety issues have been addressed. There is room for improving reliability though. For instance, in the output stages removing power transistors, cleaning the heatsinks from the old silicon compound and replacing it with new compound, will improve thermal bonding between semiconductor and heatsink. Old dry electrolytic capacitors need replacement too.

Also, since potentiometers and switches are screwed on the front panel and soldered on to the PCB, it might be a good idea to remove them individually clean them with special switch cleaner like deoxit. The old solder is also removed, the traces/joints cleaned and the components re-soldered etc.