Electronics Repair & Service

All types of guitar amp, both valve and semiconductor technologies, are repaired and serviced as required by the customer. This may range from simply replacing an input jack socket to rebuilding the output power stage of a 100W valve amp. Faulty controls on guitars can also be replaced together with pickup replacement to meet your requirements.

Repair services also extend to any piece of electronic equipment used in the music industry. Small to large scale mixing consoles, power amplifiers, powered speakers, FX pedals etc. If in doubt, just get in touch and we’ll see if we can help you. Custom Circuits Ltd is an authorised repairer for out of warranty Blackstar Amplification and Korg (Vox) equipment.

From component testing to complete amp repair

The following is a list of some of the manufacturers whose equipment has been worked on in the past. Marshall, Fender, Cornell, Victoria Amps, Music Man, Orange, Carlsbro, Vox, Matchless, Traynor, Markbass, Hiwatt, Mesa Boogie, Bugera, Peavey, Fishman, Ashdown, Ampeg, Crate, HH Electronic, Australian Monitor, Studiomaster, Soundcraft, APB Dynasonics, JBL, Behringer, Trace Elliot, SJB, Blackstar, Martin Audio, Void Acoustics, Klark Teknik, Yamaha, HK Audio, Crest Audio, BSS, Sony, Wharfedale, Cambridge Audio, QSC, Mackie, Alesis, Crown, Korg, Denon, Allen & Heath,  Yves Cochet, Zero88, Fostex, Hartke, Roland, C-Audio, Casio, Dallas, Laney, Ewave, Friedman, WEM and many others.

Amp repair steps

Amp was reported as blowing the mains input  fuse after being subjected to a power surge on a portable generator set. If you’re doing gigs at outdoor events where the mains power supply might be of poor quality, it is a wise step to invest in a mains interface unit that will protect your amp from over-voltage surges. Check the specification carefully though. Simple fast transient protection will not protect equipment from longer duration surges.

After a few diagnostic steps, the reason for the over-current condition was found to be in the right hand power amp module. The left hand module worked fine.

My assistant then diagnosed short circuit power transistors in the amplifier module. In order to locate all the offending parts, all power transistors had to be removed for further testing. Once done, another low power signal transistor was also found to be faulty. Ted isn’t good with screw drivers, so I had to do that myself!

All but 2 power transistors were short circuit so all 8 were replaced together with the additional low power transistor in the pre-driver stage. Once reassembled, normal service was resumed.

This damage could probably have been avoided if basic over-voltage protection circuitry had been designed into the power supply stage. Very often, simple protection devices will protect the circuitry against fast transients and you’ll never even know they’re doing it. However, if not suitably specified, long power surges may cause over-dissipation causing them to fail into a short circuit mode. This will result in the power input fuse blowing until the protection device is replaced, but at least the power transistors won’t need replacing as well.