Home › Forums › Vintage EHX › Vintage Small Clone MINI-CHORUS SAD1024 Help please!

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  • July 9, 2020 at 1:04 pm #86346
    FuzzyLefty77
    Member

    Hi guys,
    Apologies for my first post being a bit of a long winded cry for help but I’ve picked up a non functioning Small Clone.
    To my delight it was a vintage one from the 80’s with the SAD1024 chip. I still can’t seem to get it working after performing the following:

    Checking all resistors and polarized caps
    Checking all the trannies
    Checking the diodes.
    All the off-board stuff is good.
    I’ve tried different LM348, 4558 and the HEF4047 I/C’s to no avail.

    It passes signal fine, LED is good. No chorus effect at all though which makes me wonder if the SAD1024 is kaput?!

    I’ve taken readings from all the I/C pinouts and got the following (attached).

    The LM358N readings seems “odd” to me compared to when I’ve checked these on other pedals?!

    Any pointers would be great (or even confirmation that the SAD1024 is DOA)

    Regards,

    July 9, 2020 at 1:05 pm #126251
    FuzzyLefty77
    Member

    Sorry, posting pics on here is a bit fussy!
    Pic attached with readings

    July 9, 2020 at 2:21 pm #126252
    Scruffie
    Member

    4558 & 4047 voltages look good but yes there is a problem with your LM358, it should have varying voltages on its output pins.

    Have you checked the tantalum capacitor between pins 1 & 2? Also the solder joints on the rate pot, they often break.

    But… your SAD voltages certainly aren’t good, output DC that low could certainly imply it’s kaput… have you checked the bias and the solder joints? On rare occasion poor connection with the socket can be to blame too so its worth cleaning them.

    July 9, 2020 at 2:29 pm #126253
    FuzzyLefty77
    Member
    Quote:
    4558 & 4047 voltages look good but yes there is a problem with your LM358, it should have varying voltages on its output pins.

    Have you checked the tantalum capacitor between pins 1 & 2? Also the solder joints on the rate pot, they often break.

    But… your SAD voltages certainly aren’t good, output DC that low could certainly imply it’s kaput… have you checked the bias and the solder joints? On rare occasion poor connection with the socket can be to blame too so its worth cleaning them.

    Thanks for quick response!

    Yeah I checked the tantalum cap and it reads good.
    Completely removed the original pot (it tests good) and wired in a new pot for testing purposes so I don’t think thats an issue.

    I’ll give the solder joints and the sockets a good once over!
    The bias? You mean trim pot? That tests okay but also has zero effect when tweaked.

    Thanks again for your help.

    July 9, 2020 at 2:38 pm #126254
    Scruffie
    Member

    Zero effect from the trim pot? So does it not alter the bias voltage on the input of the SAD?

    Hmm, if the tantalum/electrolytic caps are good and you’ve tried replacing the 358 and the pot, besides bad solder joints you’d have to start looking at faulty resistors or non-polarized capacitors, not impossible but a rare occurrence. It can be helpful to check for continuity between pot and its connections for broken solder traces.

    I take it you don’t have a scope?

    July 9, 2020 at 2:43 pm #126255
    FuzzyLefty77
    Member
    Quote:
    Zero effect from the trim pot? So does it not alter the bias voltage on the input of the SAD?

    Hmm, if the tantalum/electrolytic caps are good and you’ve tried replacing the 358 and the pot, besides bad solder joints you’d have to start looking at faulty resistors or non-polarized capacitors, not impossible but a rare occurrence. It can be helpful to check for continuity between pot and its connections for broken solder traces.

    I take it you don’t have a scope?

    I do have a scope and its the next thing I “need” to start knowing what to do with it LOL. So far I’ve fixed pedals without needing it.
    Any pointers with what I need to do please?

    I’ll try tweaking the trim pot again and see what happens to the SAD.
    I haven’t looked at non-polarized caps yet. Added to the list.

    Thanks,

    July 9, 2020 at 3:23 pm #126256
    FuzzyLefty77
    Member

    Okay, trimpot does effect the SAD at pins 2 and 15. Goes from 0-6.75v What voltage should I be feeding into it?
    The outs pins 11/6 still read low.

    July 9, 2020 at 7:02 pm #126257
    Scruffie
    Member

    The output voltage should change with the input bias, go back to checking the solder joints etc. and then I’m afraid it’s probably a dead SAD if that doesn’t help.

    Your scope should show a square wave on pins 10 & 11 of the 4047 and a square on one output pin of the 358, a triangle on the other.

    July 10, 2020 at 6:46 am #126258
    FuzzyLefty77
    Member
    Quote:
    The output voltage should change with the input bias, go back to checking the solder joints etc. and then I’m afraid it’s probably a dead SAD if that doesn’t help.

    Your scope should show a square wave on pins 10 & 11 of the 4047 and a square on one output pin of the 358, a triangle on the other.

    Output voltage changes a tiny bit to 0.3v when input bias is adjusted to max (6.75v).

    Getting correct waves from all the pins you mentioned above.

    Guess I’ll try resoldering everything from the Rate pot to the LM358. Continuity seems okay but worth a shot. (the values from the LM358 are still bugging me)
    Remove and try resoldering the SAD.
    Remove all caps and test them.

    Many thanks for all your help!

    July 10, 2020 at 8:24 am #126259
    FuzzyLefty77
    Member

    Scruffie,

    Just noticed you are on freestompboxes and I posted same topic there that you’ve replied to, lets focus on that forum rather than confuse matters with cross posting here as well.

    I will just post and update on here (if I find the conclusion) to help anyones else nearer the time.

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