Blackstar Series One repair S1-104EL34

Blackstar Series One repair

This Blackstar Series One repair from February was a bit of a mess! The amp had unfortunately received the unhelpful care of another repairer who had left the amp in a terrible state. If you don’t like to see damaged PCBs, look away now.

It was brought to me because it was blowing fuses at gigging levels. The owner had bought it second hand and it had started blowing fuses recently. A quick fix was managed in time for a gig!

I’m not sure what the original fault was with this amp, but whoever had previously attempted to fix it was very much of the ‘add more solder’ school of repairing! I suspect that they had not attempted to remove the board and had just tried to repair the amp from the top side only in doing so they’d damaged to PCB and left the transistor hanging by a thread of pad..

Blackstar Series One repair3You can see the horrible original work on the left and my improved fix on the right of the image. I removed the board and cut away the damaged track and recreated a solid connection with solid core wire on the board reverse. I replaced the burnt out components nearby with suitably rated high power resistors. I also replaced the transistor.

The whole job took 3 hours and included a valve test (revealing three worn preamp valves) and an additional (FOC) 1 hour soak test at gigging levels.

If you have a blackstar series one repair, please drop me a line.

Here’s a video of the amp, once fixed.

Fender Blues Jnr Repair – Ghost Notes

Fender Blues Jnr repair

This Fender Blues Jnr repair was another urgent job completed quickly for a customer who needed it for a gig in Lincoln on the evening it was dropped off.

He brought it to me reporting that something ‘wasn’t right’ with the sound. Upon listening to the amp I could tell what he meant – under certain notes there was an odd ‘subharmonic’ type sound, ghost notes appearing underneath the played notes.

I’ve done other Fender Blues Jnr repair work in the past – but unfortunately someone else had already been working on this amp. They’d make a bit of a mess of the power amp

Fender Blues Jnr repair

Unfortunately the previous attempt at repair, though well meant, caused problems – you can see in the first two images there are lifted pads (possibly the original problem or caused by excessive heat when soldering), no solder between pin and pad on the cathode and some burning on the PCB through excess heat (this is actually on pin 3 of the EL84 which isn’t used so not a big issue).
Fender Blues Jnr repair - PA rewire
The third image is how it should look – Fender’s original soldering on the preamp valves is intact. The preamp valves have the screws closer, they’re shorter so there’s less force exerted and they’re not near the place where you’d put the mains cable.

The power valve section of the PCB was beyond sensible repair and the best way to proceed was to take out the PCB, and saw it in half, re-fit the preamp part of the PCB and wire the power stage point to point. I used chassis mount valve sockets to prevent this happening to the power stage in the future.
Fender Blues Jnr Repair 2
There were also some hairline cracks observed under the microscope which I resoldered.
Having fixed these sources of issues I was finally able to address the problem with the ghost notes. This is caused by a common problem with modern fenders – lousy filter capacitors. I was able to replace the filter caps with parts that I had in stock in order to meet the 24h deadline.

The ghost notes were visible on the oscilloscope – and so it was easy to see on the bench when these horrible sounds disappeared. You can also hear the difference in the video:

If you need a Fender BLues Jnr Repair, please get in touch.

Fender Blues Jnr Ghost Notes

Fender Blues Jnr Ghost Notes

Blackstar HT5 Repair, Keld Ampworks, Newark, near Stamford

Blackstar HT-5 repair

I’ll admit this Blackstar HT5 repair had me confused for a bit. It was brought to me from Stamford Endowed School, which isn’t that far away from my workshop in Newark, it is just down the A1.

The amp arrived with no sound output from the speakers. The valves tested fine, one 12ax7 and one 12bh7.

Looking inside the amp I could see signal on both grids of the 12ax7, but nothing was getting through to the output stage.

Using a thermocouple I tested the temperature of the semiconductors in the amp and found that the two MOSFETs were getting rather hot!

Upon inspection, I saw that somebody had drilled two little holes between the MOSFET legs and left all the swarf (mangled metal pad and PCB resin).

It turns out that there’s a forum post saying that the MOSFET pads were apparently quite close together and prone to arcing. I think that somebody read that post and decided to go DIY on this amp, not understanding that leaving chewed up pad around the holes would gonna cause a worse problem than arcing. 🙁 It probably worked for a bit but it worketh no longer.

After replacing the burnt out drain resistors and the damaged FETs, the amp was back up and running. These are really great little amps and put out a lot of volume, despite their 5W rating.

If you need a Blackstar HT5 repair, please contact me.

Powered mixer repair – Wharfedale SPX815

powered mixer repair wharfedale spx815 powered mixer

Just doing a quick write up of a powered mixer repair that’s going out today. It’s a Wharfedale repair, an SPX815 powered mixer that had no sound output from the left output channel.

My first instinct when the Newark customer contacted me was to expect that the output stage had blown, but this turned out not to be the case as I quickly discovered that the left channel was fine when a signal was plugged straight into the power amp inputs.

Powered Mixer repair Wharfedale SPX815

Powered Mixer repair Wharfedale SPX815 - botched wood screwIt’s difficult to attempt a powered mixer repair without schematics so I’m very grateful to the gentleman on a forum who sent me the schematic over. After tracing the fault through the schematic I discovered that an SMT op amp in the left channel graphic EQ was blown – there was a nice neat hole in the top.

Someone had already attempted a repair on the PA section of this amplifier – I’ve no idea what they were doing, but they’d bent the metal chassis around the PA, stripped the threading on a PEM and tried to hold the whole botched job together with a wood screw. It’s pretty much impossible to bend things like this back, but I did my best, redrilled the mounting holes and replaced the dodgy wood screw with a machine screw! I left a note to any future repairers so that no-one things the dodgy work was done by was me!

Here’s a video of the powered mixer repair:

If you need a powered mixer repair, please get in touch.