Bugera V22 reverb repair

[rsukie]

I’ve been working on getting the reverb working on an old Bugera V22. After tracing the signal, I found that the actual reverb module is working and outputting a good signal, but the switching circuit that turns the reverb on/off by grounding the effect output was keeping it off. Im using the unofficial V22 schematic that’s been floating around for years. I’ve included the section of interest here. Transistor T7 does the effect on off switching based on T5 being switched by a flip-flop output. However I don’t see any way that with the signal being connected to the base to T7 as shown this would work. It’s almost like the base and collector should be swapped, but if the transistor is actually a DTB113, then from what I’ve ohmed out, this schematic is correct. Am I missing something here? I did confirm that T5 is switching correctly, driving the collector to 0 when on. I also removed T7 and the reverb does work then (although obviously can’t be switched off). So in any event, I believe T7 is bad, but I’m not convinced it’s a DTB113 and since it’s an SMD part, I can’t make out any markings. Or is there some way that the circuit as shown can actually function with the output coming from the base?

[g1]

How about T5, is switching signal really going to emitter like that, and not the base? And T3 collector is tied to footswitch jack?
Seems like lots of questionable stuff there.

[Jazz P Bass]

It appears that T5 & T7 are wired as a Common Base configuration.
Input at the Emitter.
Output at The Collector.
T7 is an odd transistor with built in resistors.

[rsukie]

For posterity, I’ll answer my own question here. After a lot of magnification and research and digging into nearly invisible SMD marking codes (6S on this device for anyone interested), I found that transistor T7 is misidentified on the schematic. It is actually an N channel FET MMBFJ113. With the pinout for this device, it makes much more sense. Gate is connected to R19, Source to ground and Drain to R74.

[rsukie]

Replaced T7 with a new MMBFJ113 and we have working reverb switching again. Lots of anxiety and magnification and steady hands needed to get this VERY tiny SMD part aligned and soldered in place successfully, but it worked!