Back in August of 2017, one of these combo bass amps came through the Unbrokenstring Shop with cracked solder joints, which were probably a result of brittle lead-free (RoHS) solder on the circuit board. The owner of this Ampeg saw that post and called up the Unbrokenstring Crew to ask if this amp could be fixed as well. Here we go!
Disassembly and reassembly of the combo amp is exactly the same as was performed on the earlier post. Here, we are starting this blog post with just the chassis on the bench.
Name, Rank, and Serial Number, please!
From above, everything appears to be as it should be. No wires are hanging loose as was seen in the amp serviced in August, 2017.
But once the circuit board was removed from the chassis, this rotary switch came loose from the circuit board!
As was seen in the other repair, the metallurgy involved with the soldering process was to blame. In addition, in my opinion, this switch was not the exact part that matches the footprint on the circuit board. Note that the pins are bent inward to the center of the switch.
These pins are plated in gold. This is a good thing for the component, but gold, in solution with molten solder (yes, the metals mix) makes the resulting solder joint brittle. Here, some activated rosin flux is added to the gold plated pins to prepare them for a coat of tin-lead (non-RoHS) solder.
Tinning is complete. In this picture, we can see the intentional bending of the legs to match the holes on the circuit board.
This is a high quality part, and works well in this application. However, the manufacturing engineer at SLM was off his/her game that day.
Our new solder joints will probably outlast the amplifier.
No parts were required for this repair, only labor. This unit plays 100% now!
See the previous Ampeg 115 post for reassembly.
Thanks for reading all the way to the end!
CONTACT – David Latchaw EE