SOLVED Me again...........Tayda EA Tremolo PCB not working

[Jeff C]

Hoping I don't set another record with this one, but I've just finished building an EA Tremolo from a PCB from Tayda. The Tayda forum is useless. No answers, no activity. So, I hope the patient and helpful folks on this forum who got me eventually across the Cobalt Drive finish line (which by the way sounds fantastic!), can figure out what my problem is. Once I finished it and plugged it in, I got audio but no effects. The LED stays lit up whether the switch is off or on. Volume trimmer potentiometer seems to work fine. I do have the input and output jacks wired correctly p), and am getting positive (not negative ) 9 volts to the board. I've posted four pics below (figured out the magnifying bar on the mag-lite app -doh!). Given my transistor trauma of the Cobalt Drive build, I'm suspicious of mine on this one, so I took some close up pics of those. They Tayda build instructions were confusing. https://www.taydakits.com/instructions/ea-tremolo/pages/designators-and-components--43. For one, it lists a C4 cap, but there is no place for it on the PCB. It also says to use the N5457 and the SMD for Q1 and Q3. Tim (Fig) told me to use one or the other so I used the 2N5457, perhaps unwisely. They look pretty gnarly in the pics.
Here are some voltage readings from the transistors:
Q1: G: 9.3; S: 5.65; D: 4.46. Q2: E: 2.24; B: 2.8; C: 2.18; Q3: all 0's (hmmmmm); Q4: E: 0; B: 4.61; C: 2.55.
Also, C2 reads 4.4 on the negative pin and 5.6 on the positive one.

I tested with the audio probe and get a signal most everywhere but nada from any of the pot pins.....

Any suggestions on where to start would be appreciated! Tks.

Jeff

 

[Jeff C]

That would be great! I have some value left on my gift card, so I’d be happy to pay for them. Tks!

 

[mybud]

FWIW do consider socketing your transistors for future reference. First, it avoids the real possibility of overheating them during installation and second you can swap and replace them afterwards to your heart’s content. If you are concerned about them eventually working loose, a small dab of solder will secure them in place after you’ve verified the circuit works according to plan.

 

[benny_profane]

Socketing is not a bad idea if you want to audition parts and is particularly helpful for ICs since they are very difficult to remove once soldered. However, if you are overheating Si transistors to the point of damaging them, you should work on refining your soldering skills.

 

[Harry Klippton]

@Jeff C while you're waiting for your replacement 5088, try reflowing the one that's in there. Bad solder joints are much more likely than bad transistors

 

[Jeff C]

Will do!

 

[mybud]

Socketing is not a bad idea if you want to audition parts and is particularly helpful for ICs since they are very difficult to remove once soldered. However, if you are overheating Si transistors to the point of damaging them, you should work on refining your soldering skills.

Yes indeed noted, @benny_profane. I have never burned out a silicon warrior myself, naturally. I wonder if @PedalPCB might entertain the thought of a lie detector PCB in due course (just for me, that is).

 

[Jeff C]

I wanted to help, but then Chris posted a meme so I'm outta here.

BTW, you read Q1's voltages backwards. Should be D-S-G.

Q1 is ok.

Q2 is saturated. Verify R9 and look for shorts.

Believe it or not, Q3 should be all zeroes. The gate voltage will vary if the LFO is running, which it's not.

That brings us to Q4. The only reading there that makes sense is E = 0. If B is really 4.61V then that transistor is FUBAR. Which might explain why the LFO is not running. Recheck your readings, inspect for shorts, etc.

I forget, what was the root cause of the Cobalt failure?

Rechecked Q4. Readings are the same. Cleaned it up. Pic below. I verified R9 (4.7K).

 

[giovanni]

Rechecked Q4. Readings are the same. Cleaned it up. Pic below. I verified R9 (4.7K).
View attachment 27697

I think you may need a bit more solder.

 

[Jeff C]

 

[PJS]

Yep. my first thought was that was clearly a before pic. (before soldering I mean)

 

[Jeff C]

Brief intermission: while awaiting a replacement 5088 for the tremolo pedal, I finished building the Tayda BSIAB2 distortion pedal (again, bought because I kept forgetting other items for the infamous Cobalt Drive experience - buying all my PCB’s from PedalPCB from now on!). Before plugging it in I got on my knees and prayed to all the gods of music (https://deities-by-abode.fandom.com/wiki/Gods_of_music - to my dismay the list excludes Nandi, the bull god who creates the music that Shiva does his dance of creation and destruction to, my favorite). I thought about adding Oedipus, given we are talking about foot pedals, but decided his chequered past and the fact he wasn’t actually a god disqualified him.

It didn’t work.

I was getting audio all over the PCB but nothing going out. But I figured out the problem (apart from wonky cables): the wire from the PCB to the switch daughterboard was loose at the daughterboard and a couple of wires needed to be cleaned up. And presto, distortion pedal works like a charm. Still have to drill the enclosure and add an LED (ummm, I burned the one out when I actually touched it to power on the other side of the resistor - dang). Then make the decals and spray that sucker. Victory is mine.

 

[Jeff C]

So, did you miss me? Sadly, I replaced the Q4 5088 but no luck. Voltages are now 3.66, 0.61 and 0, however, different than before. Same problems, though. To recap. I get continuity between all the components on the schematic. I did an audio probe. I get audio all the way to and including the volume pot. But on the path to the depth pot, audio stops at the drain pin on Q3. There is no audio on the gate pin and no continuity between the gate and drain pins. Voltage is 0 on all three pins. There is continuity between the gate pin and two of the depth pot pins. Do I conclude that Q3 needs replacing?

 

[Jeff C]

Did everyone get bored with me? . Really do need some input if you’re not. Plus, well, I have another pedal I built that worked fine before stuffing it in the enclosure and now nada. But I’ll keep at that one on my own for now. Meanwhile, any useful suggestions re the tremolo would be most appreciated!

 

[jimilee]

You should have continuity between the led and Q4. It will stay lit, if you look at the schematic, it’s always in the 9v path.

 

[Jeff C]

Thanks! Yes, I do have that continuity. But I still get no audio out. Any suggestions?

 

[jimilee]

You should have voltage if you have continuity. There’s my confusion.

 

[Jeff C]

There is voltage on Q4 (3.6; .6 and 0), but none on Q3. But Buddy says that there should be none there anyway.

 

[jimilee]

There is voltage on Q4 (3.6; .6 and 0), but none on Q3. But Buddy says that there should be none there anyway.

Yep. Have you reflowed all your solder joints and triple checked your resistor values?

 

[Jeff C]

I’ve checked the resistors but haven’t reflowed all the solder. Did replace the Q4 transistor.

 

[Jeff C]

Was hoping for some advice re to where I might want to start resoldering based on the info I provided. I guess replacing the Q3 because that’s where the audio trail stops is not a useful strategy?