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

 

[BuddytheReow]

The actual tremolo section is in the right 1/3 of that schematic. The left 1/3 is merely a booster stage and that checks out. I’ll wait for Chuck to chime in with his thoughts

 

[Chuck D. Bones]

How did the visual inspection go?

If you're going to replace parts at random, then my troubleshooting methods are of no use.

Would be helpful if the schematic had component values on it. Not my job to look up the BOM or find a better schematic.

Seems like things start to go haywire at Q2, so let's focus there for the moment. According to your measurements, Q2 is saturated. So it's no surprise that the signal is messed up there. Make sure R5-R9 are the correct values.

Q3 all pins 0VDC is normal.

 

[Jeff C]

So the visual inspection looked ok to me. I did clean up a few things but did not see anything my untrained eye found questionable. It was Q3 that I replaced because it seemed to me the problem starts there. But that didn’t fix things. R5 and R9 are 560k and 4.7k respectively and color match those from my original order. I tried reading the resistance on the board but can’t get a clear #. Q2 is a 2N3904 and ita voltages now read E: 2.15; B: 2.81; and C: 2.24 (close to first time I measured them).

 

[Jeff C]

And here‘s the BOM.

 

[Chuck D. Bones]

Looks like Tayda swapped R5 & R6 on their board. Here is a correct schematic. For future reference, I will not be assisting with troubleshooting Tayda projects since they can't even get the build docs right.

 

[Jeff C]

Looks like Tayda swapped R5 & R6 on their board. Here is a correct schematic. For future reference, I will not be assisting with troubleshooting Tayda projects since they can't even get the build docs right.


View attachment 29725

Tks! So, I should just swap those two? But there’s ALOT different between those two schematics……

 

[music6000]

Looks like Tayda swapped R5 & R6 on their board. Here is a correct schematic. For future reference, I will not be assisting with troubleshooting Tayda projects since they can't even get the build docs right.


View attachment 29725

 

[Chuck D. Bones]

Thank you Phill, thank you very much!

 

[Chuck D. Bones]

Tks! So, I should just swap those two? But there’s ALOT different between those two schematics……

If you want it to work, then you should swap them.

You could change parts as req'd to conform to the schematic above. They only stupid thing they did there (which Tayda also did) was put two capacitors in series. C2 might as well be a jumper because when you put a 10uF and a 220nF cap in series, you get a 215nF cap.

You can read about the EA Tremolo here:
http://www.generalguitargadgets.com/effects-projects/tremolo/ea-tremolo/

 

[Jeff C]

Thank you!

 

[Chuck D. Bones]

Sadly, the original article in Electronics Australia is no longer available for free download because the copyright holder thinks it's better for us to pay him for a scan of a back issue from November 1968.

Phill, maybe you can have a word with Nicholas Vinen and appeal to his better nature.

https://worldradiohistory.com/Electronics_Australia_AU.htm

 

[music6000]

If you want it to work, then you should swap them.

You could change parts as req'd to conform to the schematic above. They only stupid thing they did there (which Tayda also did) was put two capacitors in series. C2 might as well be a jumper because when you put a 10uF and a 220nF cap in series, you get a 215nF cap.

You can read about the EA Tremolo here:
http://www.generalguitargadgets.com/effects-projects/tremolo/ea-tremolo/

I knew you would be back!!!

 

[Chuck D. Bones]

Somebody has to help Jeff out and you were busy troubleshooting a Kliche Mini.

 

[Jeff C]

Well, I swapped R5 and R6. Still no tremolo effect but the audio I do get is now very strong and clear, unlike the distorted static-y sound before. Just no tremolo. audio probe on the depth and speed pots yields nada, same with C8, 9 and 10. I noted two other differences between Tayda and the genuine schematic. C5 and C3 on the genuine one are 47n and on Tayda they are 470n. And on the genuine one R12 is 15K but only 10K on Tayda. Not sure if that makes any difference re my problem.

 

[Chuck D. Bones]

Progress!
An audio probe is not much use when testing an LFO. We're referencing the schematic I posted, right? That sch has a typo: Q2 (2N5457) should be labeled Q3 and the 2N5088 should be labeled Q4. Either set of values for C3, C5 & R12 should be ok. I'd recommend leaving them as-is. Check Q4's voltages again, because there might be an error in your previous measurements. The base voltage should never be higher than the collector in that circuit. If the LFO is running, you should see Q4's collector voltage wander around by a several volts on the DVM. Make sure the +end of C6 connects to Q3-C. Make sure the +end of C8 connects to Q3-B. C7 doesn't matter.

 

[Jeff C]

Will do!

 

[Jeff C]

Q4 is now 0.0 for E; .61 for B; and 3.68 for C (different than previously, with B now reading less than C). But C stays steady at 3.68 with no variance.
C6 (on your schm) does NOT have continuity to Q3-C; it DOES have continuity to Q4-C (not sure which end is positive but I do get connectivity from one of them). C8 does NOT have continuity to Q3-B, but DOES to Q4-B.

 

[Jeff C]

Victory!! And again, it was not the salmon mousse this time. Based on all your wise counsel, I figured my problem lay somewhere between Q4 and the speed pot. So, I checked for the umpteenth time continuity and discovered that while I would get a beep on C5 and C6 (on the genuine schm), it was intermittent. So I decided what the hell, reflow those two puppies. And yes, you all told me so, it was my solders on one or both of those caps (besides the swapped resistors on the incorrect Tayda schm that Chuck wisely revealed). Trembles like a leaf now! Only 79 posts this time. I’m improving! Tks, everyone for all your help. Now back to the Magnetron once my replacement op amps arrive.

 

[Chuck D. Bones]

You should be able to spot bad solder joints visually. Maybe better light and more magnification would help.

 

[Jeff C]

They looked pretty good to me. I had good light but didn’t magnify……..next time for sure! Tks again, Chuck.