Dandy Horse - no output

[Scruffie]

Sorry to hear you're still having trouble! Well it definitely sounds like a cap problem with its cyclic nature... C4 & 6 would be possible suspects to try replacing too, I highly doubt it's related to any film or ceramic caps.

I think I spot some Chang brand caps so am I to assume some of the parts might be from Tayda?

[Vivek_rc]

I just a minute ago replaced C6, same issue And will try replacing c4 as well and see how it goes. And yes some of the caps are from tayda. I see how I go and maybe get better caps if problem still persists. Hey man thanks a lot for your advice and support, I appreciate it.

[Vivek_rc]

I’ve replaced both caps and pin7 voltage is really intermittent, sometimes it goes to 6.2v and sometimes it drops to 2V, and sometimes it’s just fluctuating Between 2 to 4 V really weird. I’ve left it running and will see in the morning again. Also ordered two more N571 just in case....😕.

[jimilee]

I would reflow all the sketchy looking solder joints.


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[Vivek_rc]

I’ve ordered some Panasonic electro capacitors and will replace all the electro caps connected to IC2. I’m also going to replace the IC socket for IC2 just to rule it out. Also got a new NE571 on the way. Although this is frustrating, I’m learning a lot and looking at this as a challenge to get this working. Will report back on how I go in a few days, thanks again for the support Scruffie and Jimilee

[Vivek_rc]

Here’s the update . I replaced IC2 socket, replaced c4, c6, c7 with Panasonic caps and evening put in a new ne571, same issue, wasn’t working. Replaced C27 thinking it’s linked to IC2 might help, didn’t solve the problem. I put back in original v571.

Was about to throw in the towel. But Scruffies comment on Tayda caps kept ringing in my mind, so on a whim decided to replace C54 and C63, the two 100uf caps, with Panasonic caps. No logic behind it.  And circuit started to work as expected and it’s been running now for 3 hours the voltage on pin 7 has remained stable at 7V and getting a modulated output.

Will keep it going for a few more hours and see if any issues come up. It’s only been running in the flanger mode.

Was trying to read up to see how the caps for the voltage regulator could have an effect on the NE571, would be interesting to know.

So should I throw out all my tayda electro caps ? Never had an issue for my other builds until this one....

[Vivek_rc]

No good, after a few hours Pin 7 is now sitting on 14V and sometimes drops to 7V and then back up to 14V. I’ve got some 22uf electro caps on the way, going to replace all of the caps so there will be no Tayda sources electro caps on the board. Will check in again in a day or so

[Scruffie]

So should I throw out all my tayda electro caps ? Never had an issue for my other builds until this one....

See, there's the problem with Tayda, 99% of the time, the parts are fine, but that 1% means having to and being able to track down what didn't work.

But honestly, seeing as you replaced all the caps around the compander, I'm a little stumped as to what's going on... It would be logical to expect voltage variation elsewhere in the circuit if it was an electro elsewhere.

I do wonder if taking IC1 & IC6 out of the socket and keeping the test going might help, you've switched the compander but if one of those had an intermittent problem (odd as that would be), it could potentially cause a problem downstream...

Definitely a tricky problem that either I'm missing an obvious answer to or is just uniquely strange.

[Vivek_rc]

Hi Scruffie

I removed IC1 and IC6, and upon startup voltage on pin7 of IC2 was sitting at 7V, and after a couple of minutes it’s now sitting at 14.15V, and remaining at this voltage.

[Vivek_rc]

Hi Scruffie

I’ve been trying to troubleshoot further, checking for an shorts or bridges and at the latest check of the voltages on IC2, I see The voltage on pin 5 and pin6 of IC2 is now at 1.2 V and pin 7 still on 14 volts. All the other pins on IC2 are as per the expected voltages. I’ve reflowed all the solder joints as well. Audio probing the signal path it does work up until the output of pin 11 and 10 of IC2.

Really scratch my head with this one

[Govmnt_Lacky]

Do you have any electro caps that are rated at less than 25V in the circuit?

Just trying new ideas 

[Vivek_rc]

Hi Mate,

non of them are below 25V. But what I am planing to do is replace all the 22uf caps with Panasonic caps and also replace the 220uf cap as well. Should get them by Monday. This replaces all the electro caps from Tayda.

Keeping throwing forward any ideas, all appreciated and will be tested

[Haberdasher]

Sometimes when I have a weird voltage/amperage problem I can't figure out I've solved it by re-booting my power supply, changing out the power cable, or even changing which port the cable is plugged into.  Then again, the power supply on my bench is one of those cheap $30 ones from Amazon, so...

[Vivek_rc]

That's the type i am also using  . I just powered up the pedal just then and it's working perfectly. Disconnected power  and reconnected, working as expected, voltages on IC2 all check out as expected values . But if i keep it running for some time then the problems start. I will next power it with the isolated power supply from my pedal board, see if it makes a difference. but will also replace all the remaining electro caps from tayda with panasonic ones and hope by some luck it fixes it .

[Vivek_rc]

I’ve had some success running the pedal with an isolated power supply, getting a modulated output and it’s been running on a loop for a few hours now. However there is a fair bit of white noise coming through as well.

I will replace the 220uf electro capacitor (I think for power filtering, I used an old one I pull out of another test circuit), with a new one that’s coming in this week, hopefully gets rid of the white noise. I have already replaced the two 100uf caps on either side of the 78L15.