Broken vintage delay pedal. Where to start?

Discussion in 'Burnt Fingers DIY Effects' started by NorthenLights, Apr 29, 2021.

  1. NorthenLights

    NorthenLights Tele-Meister

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    I haven't used my Pearl AD-33 two channel analoge delay pedal for quite some time, but I got some feeling today and plugged it in. I was really disappointed to realize that something has happened to it since last time.

    First off, no sound when bypassed. When engaged, the effect LED flickers like crazy, and ocationally goes out completely. The channel select LED works fine. The pedal spews out this loud buzz, kinda like a waterfull, but the signal comes through, albeit weakly. No delay at all at channel one, but channel 2 is working, although with the noise remaining.

    Any suggestions for where I should start trouble shooting?
     
  2. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Have you opened it up and taken a look for any "bad" looking components?

    I'm not familiar with the pedal. Can it be powered by battery and by adapter? Have you tried both?
     
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  3. Greg70

    Greg70 Tele-Meister

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    I'm not familiar with that pedal. I did a quick google search and found this image of the back of it. It says a flickering LED is low battery. It looks like it takes two 9V batteries and runs on 18V. If you haven't tried new batteries that's the first place to start.

    After that, I'd remove the screws at each corner and have a look at the circuit board. Apparently these were made in the 80's. If they are that old, it's possible that it has some electrolytic caps that are shot. Share some pictures to the board.


    upload_2021-4-29_8-50-22.png
     
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  4. fidopunk

    fidopunk Tele-Holic Gold Supporter

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    I had an old, old, old DOD combo pedal that was delay and overdrive with very similar symptoms. For whatever reason, and I have no idea why this happened as I never really tracked down the circuit, I replaced only the LED and the pedal came to life.
     
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  5. Peegoo

    Peegoo Poster Extraordinaire

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    The best place to start is with a schematic, and using a meter to check the simple stuff first, and move to the more complex if no problems are discovered.

    Problems like this are most often power issues.

    Stomp boxes take a specific voltage at their power jack and most step down that voltage to other levels to run various sections of the circuit--just like how an amp does. If any power rail is outside of spec, that portion of the circuit can become unstable or stop working altogether.

    Capacitors go bad, that is usually the reason power becomes unstable. Look for a leaking/crusty or bulging cap. Not all bad caps leak or bulge, but many do.
     
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  6. ElJay370

    ElJay370 Tele-Afflicted

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    My first steps with old pedals that are acting funky is to open them up, check for anything obviously loose, burned, or broken, blow the dust out, carefully spray a bit of contact cleaner into all pots and switches, and install a fresh battery.
     
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  7. kbold

    kbold Friend of Leo's

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    ...... and install fresh batteries.

    Test with an 18 V power plug, if you have one.
     
  8. Engine Swap

    Engine Swap Tele-Afflicted

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    Always start with the power supply/section
     
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  9. ICTRock

    ICTRock Tele-Afflicted

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    with a pedal that old I would literally replace all the electrolytic caps as a matter of course just like recapping a vintage amp ... it is expected. if that didn't solve it I would verify all ground connections first then start tracing voltage around the circuit from the power in. if that all checks out, time to break out the audio probe and figure out where you stop getting sound
     
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  10. TwoBear

    TwoBear Tele-Afflicted

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    A lot of great input. I might add to double check the voltage/polarity of whatever 18 volt adapter you may use, as the older pedals don't have provisions for reverse polarity quite often. It's definitely a good sign that you're getting delay, as a lot of those old Reticon/SAD chips are either discontinued or extremely expensive or are being remade, but expensive and it's just so much cooler if they're working. I've heard of LEDs hindering playability and I wonder if some of the old designs used the LED as a safety measure towards reverse polarity? Purely just a stupid guess on my part. I would definitely inspect the barrel power Jack if it has one, and double check the polarity, and intermittent connection.
     
  11. NorthenLights

    NorthenLights Tele-Meister

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    Lots of great answers guys! I'll pull it apart when I get home, and post some pictures.

    I don't use batteries, but a quality True Tone power supply. Polarity is center negative. One can just hope it will be something easy, like the led.
     
  12. JuneauMike

    JuneauMike Poster Extraordinaire

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    Last edited: Apr 30, 2021
  13. NorthenLights

    NorthenLights Tele-Meister

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    Ok, I think we might have a suspect! I took the pedal apart, and the components all look ok, at least on the surface. Taking a closer look at the pcb however I found this bad boy, right underneath the power input.


    Thought it was a cold solder joint at first, but after removing some of the excess solder, it looks like a solder ear (is that what they're called in english?) has come lose.


    What's the best way to fix this?
     
  14. JuneauMike

    JuneauMike Poster Extraordinaire

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    Can't tell by the lighting, but is that an input jack?

    I wonder if you could power it up and run a jumper between the solder joint and the next component down the line from it to see if anything changes. It looks like a solder pad lifted maybe and from that cold nodule there like someone attempted to jumper the solder onto the trace. Is the trace cut, or is there just crud on the board to the left of the solder.

    Maybe another course of action if you've worked with PCBs before is to remove some of that solder to get a better look at what's going on underneath. A freshly tinned tip and a solder sucker would be the tools to use there. But YMMV.
     
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  15. NorthenLights

    NorthenLights Tele-Meister

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    It's the DC jack. Sorry about the bad pictures, I'm note very good with cameras.

    Another mystery that stood out was this. A bunch of wires coming up from the pcb with electrical tape around them.


    I could'nt see this in the gut shots from freestompboxes, so I opened up the tape. I found this.


    I may be wrong, but isn't this a transistor used for surge protection?
     
  16. JuneauMike

    JuneauMike Poster Extraordinaire

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    It kinda looks like a voltage regulating something or other. I would think the three wires would be Base, Collector, Emitter, but that's just a guess. I wonder if its similar to a 2SA_* transistors that they used in the Pearl F-605?

    Pearl - F-605.jpg

    But if you've got a bundle of wires taped and zip tied together that would obviously appear intentional. And since it's worked well for you in the past I'd guess they wouldn't be the first place that I'd begin my hunt.

    Problems at the power source (input jack) would probably create a lot of mischief with the circuit, as has been said in this thread. It would be great if your problems come from a simple broken solder at the input jack. Good luck.
     
    Last edited: Apr 30, 2021
  17. NorthenLights

    NorthenLights Tele-Meister

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    Ok, some progress has been made. I removed the lose solder ear. It was where the back of the DC input was connected. I soldered a small jumper from it onto the pcb, and checked for signal in the next connection. Plugged the pedal in, and voila! Now the effect works on both channels again, as well as bypassed! The noise went down, but is still there. I remember the pedal sounded like this back when I powered it with a random walwart, but it went away after I got a regulated power supply capable of delivering 18 volts.
    Also, this is not so much a two channel delay, but a single channel with switchable settings. Whenever I switch settings the noise actually goes away, but returns as soon as I play something. I take it that something is happening in the delay circuit.
    Where should I go next? Grateful for any advice!

    As a side note, someone had scraped on the pcb next to it to lay the copper bare and put solder on top of it to connect the DC input. Makes me think that this pedal has either been repaired before or was badly put together in the factory. That transistor connected by wires also lends to this theory. In the gut shot from freestompboxes, you can see that transistor being mounted to the board the usual way.
     
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  18. kbold

    kbold Friend of Leo's

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    If you have a CRO you may be able to track down the noise source. This would be the cheapest/easiest way.
    If you don't have a CRO, I would be replacing all electrolytic caps, as per ICTRock's recommendation. Best to buy good quality caps.
     
  19. richbike

    richbike Tele-Meister

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    probably just needs 12-18v to have enough headroom if thats what the circuit specified
     
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