Home › Forums › Vintage EHX › HEELLPP!!! Original PolyChorus Issues

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  • June 24, 2016 at 11:03 pm #84459
    vinxs
    Member

    Hi All,

    Recently got my hands on a Original Polychorus and was so disappointed to find out i wasn’t getting any modulation when i pressed the footswitch, well, i do , but very faint. If i strum the guitar i get a crackling (sounds like dirty pods) sound.
    –
    Im fairly tech savy any help would be greatly appreciated…
    –
    I’ve attached a video of my issue,
    main concerns are at the
    5 second mark
    & 1:23 min mark
    –
    https://www.youtube.com/watch?v=Ewnyqhhig0U

    https://dl.dropboxusercontent.com/u/8120412/Poly/20160623_030304_001.jpg
    https://dl.dropboxusercontent.com/u/8120412/Poly/20160623_044152.jpg
    https://dl.dropboxusercontent.com/u/8120412/Poly/20160623_044212.jpg
    https://dl.dropboxusercontent.com/u/8120412/Poly/20160623_044424.jpg
    https://dl.dropboxusercontent.com/u/8120412/Poly/20160623_044033.jpg

    June 25, 2016 at 12:57 pm #121658
    Scruffie
    Member

    Post voltages of all the ICs please.

    June 28, 2016 at 7:40 pm #121684
    vinxs
    Member

    OK, being unfamiliar of where to test the voltage points,
    i checked all the solder joints to find a few loose ones, after re-soldering them that crackling sound stopped. ;)

    However, when i engage the footswitch i notice a significant drop in volume compared to the bypass mode(OFF), (with the Blend in the OFF position, Blend in the ON volume is of matched level.

    Is this normal behaviour on these old pedals?
    Or a common fault perhaps?

    Anymore info on this would be greatly appreciated :P

    Cheers

    June 28, 2016 at 7:56 pm #121687
    Scruffie
    Member

    Ya put your multimeter to the 20V DC setting, black to ground (so the enclosure) and red to the pins of all the ICs to test the voltages.

    Great, glad you managed to get that sorted.

    I think I follow you regards blend and bypass levels, so are you saying when you have only wet signal (so in chorus mode you’re getting vibrato) the volume is dropped compared to bypass? If so that may simply be a case of the gain trimmers being out of alignment.

    Do you have a scope or an audio probe for setting them?

    June 28, 2016 at 8:07 pm #121688
    vinxs
    Member

    Thanks Scruffie,

    I do have an oscilloscope, but im still learning how to operate it, thanks so much for your advice, im going to take it to a pedal repair guy down here in Melbourne, hopefully he will be able to adjust it ;)

    Cheers

    July 14, 2019 at 3:19 pm #125381
    vinxs
    Member
    Quote:
    https://www.dropbox.com/s/r7bd9b4qhiuy67e/EH7700-E.jpg?dl=0
    July 15, 2019 at 4:17 pm #125383
    Scruffie
    Member

    Without checking the schematic I can already tell you, your LM324 should have some moving voltages on it and the voltages on half your 571 are way off.

    My suggestion would be to start by just replacing all the electrolytic and tantalum capacitors first of all (unless you want to individually test them, but I wouldn’t personally bother), they’re probably 40 years old by now and they’re the most common issue I find in repairing old EHX.

    Good news is that your clock and SAD voltages look good.

    July 15, 2019 at 5:42 pm #125384
    vinxs
    Member

    Thanks Pal !!!

    I cant begin to thank you enough!!!

    thats great news about the SAD1024’s .

    Knowing that, its given me confidence to spend more time on it replacing the caps ;)

    Cheers !!

    July 17, 2019 at 1:00 pm #125391
    vinxs
    Member
    Quote:
    Without checking the schematic I can already tell you, your LM324 should have some moving voltages on it and the voltages on half your 571 are way off.

    My suggestion would be to start by just replacing all the electrolytic and tantalum capacitors first of all (unless you want to individually test them, but I wouldn’t personally bother), they’re probably 40 years old by now and they’re the most common issue I find in repairing old EHX.

    Good news is that your clock and SAD voltages look good.

    Scruffie, when you say change out the “tantalum capacitors” does that include the greenies? or just the x2 blue and x2 brown ones roughly in the center of the board?

    Electrolytic im guessing the grey littlie barrels and the x2 blue bigger barrels.

    p.s does this ceramic one physically look ok to you?…

    cheers pal!

    July 17, 2019 at 1:12 pm #125392
    Scruffie
    Member

    No, the greenies and circular (and that red square one) are mylar and ceramic non polarized capacitors, they very rarely go bad and should be left alone.

    Just those 2 blue and 2 brown in the centre as you say and the electrolytic are the barrel shaped capacitors.

    You MUST make note of the polarity of these capacitors when replacing them (I usually take a couple of photos and then use a sharpie to mark the board before removing them) the stripe on the barrels indicates the negative and on the tantalums they should have a + symbol.

    Also you need to make sure the voltage rating on the new capacitors is equal to or greater than the original you’re replacing.

    July 17, 2019 at 4:31 pm #125393
    vinxs
    Member

    Ahh great!! good thing i confirmed with you.

    Yep familiar with the polarity caution with the axial caps ;)

    thanks mate ;)

    July 21, 2019 at 3:16 pm #125399
    Frandid
    Member

    Be very cautious with the 2 SAD1024A, they are fragile and the slightest short will burn them. I own the same pedal, it only had one trouble 2 years after purchase, circa 1982, one of the SAD1024A died -the pedal had no sound- I replaced it (they were cheap at that time now they are out of price) it still works fine now. It is my favourite chorus pedal and I have a lot.

    July 21, 2019 at 3:20 pm #125400
    vinxs
    Member
    Quote:
    Be very cautious with the 2 SAD1024A, they are fragile and the slightest short will burn them. I own the same pedal, it only had one trouble 2 years after purchase, circa 1982, one of the SAD1024A died -the pedal had no sound- I replaced it (they were cheap at that time now they are out of price) it still works fine now. It is my favourite chorus pedal and I have a lot.

    Cheers Frandid, yeah im very cautious of them, thanks for your reply ;)

    July 29, 2019 at 2:41 am #125408
    vinxs
    Member

    OK!!

    Changed out the x2 electrolytic and x3 tantalum caps, and replaced all the wires. [strong][/strong]

    Ive noticed some improvement, that violent random abrupt distortion sound has gone which I’m wrapped about, but the general volume drop when the effect is activated is still significant, i can hear the modulation very faint , the drop is even more apparent when the “Blend” Switch is ON.[strong][/strong]

    You were quite right with the moving voltage on the LM324 chip, (pin labeled 1.6v was ramping up and down between 6.5-8.2)[strong][/strong]

    Im in the process of making an audio probe, what would you suggest i try next pal? replace the “NE571N”?[strong][/strong]

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