Month: September 2017

Bugera V22 Infinium Combo Amp Repair

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This beautiful combo amp excels in all categories except one…  no audio out.  Could the Unbrokenstring Crew help?

Taking a walk-around, the rear panel tells us that this amp was built in Macao, PRC.

Good corporate branding…

The TRIODE/PENTODE switch is advertised as a ‘half-power/full-power’ switch.  The LEDs labelled “Tube Life Monitoring” light up when the fuse in the plate circuit open, due to an internal short in the tubes.

Looking down from the end shows a handsome front panel with the Very Cool chicken head knobs.

The top view of the chassis shows us another good instance of strong corporate branding. I do like the protective cage over the vacuum tubes.

Here we get a good look at the bottom of the main circuit board.  I am not a big fan of soldering tube sockets straight into a circuit board, but this seems to work here.

Most everything on this side of the circuit board appears to be OK.

I was documenting the location and orientation of these cables, in case we needed to further disassemble the unit.

These solder joints appear to be cold.  We have found our intermittent ‘no sound’ cause!

Every other solder joint is removed, fluxed, then resoldered.

Ah, that’s better!

Ironic that just a couple of cold solder joints would bring this wonderful combo amp to its knees. This guy is 100% now!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Wireless Shure SM58 Battery Leaked

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This microphone was part of the estate of an amateur journalist. As she moved into treatment and into hospice, there were other concerns besides removing the batteries from unused equipment. Could the Unbrokenstring Crew revive this unit and make it usable again?

This microphone is a basic SM58 capsule coupled to a battery-operated VHF FM transmitter.

These are often seen in many performance venues as well as in worship, news-gathering, and business settings.

 

The 9v battery has leaked.  We will need to disassemble the unit to clean up the mess.

 

These VHF units are on frequency allocations that are shared with other services and may be subject to interference.  However, these units work well if you are fortunate enough to be in a part of the country where interference is low.

 

The microphone capsule is built into the head of the microphone, which unscrews from the electronics.  Connections between the capsule and the electronics are reliable regardless of how many turns are necessary to tighten the threaded bodies together.

 

The gold fingers touch those rings seen in the previous picture.

 

This inside snap ring keeps the electronics inside the housing.

 

Before we remove the electronics,we need to get the switch actuators out of the case.  The cover removes easily enough.

 

The switch actuators come straight out.

 

This is looking good!

 

This is the complete analog FM transmitter.

 

Working with the battery contacts is much easier now that the case is out of the way.

 

Reassembly is the reverse of disassembly.  Wow, that’s profound…

 

These big tweezers are all I need to get the inside snap ring back in place.

 

Reassembled, the new battery is installed and we have a green light!

 

The receiver indicates that an FM carrier is present.

 

We have an intermittent problem with audio out of the microphone.  We need to look at the capsule.

 

I guess we’ve screwed the pooch by now.

 

The wires are cracked where they emerge from the solder joints.  These will be reworked.

 

This brass adapter goes between the capsule and the rest of the housing.

 

We are back together again!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626