Home › Forums › Help/Technical Questions › Vintage Small Clone No Signal At All Problem

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  • January 14, 2011 at 11:37 pm #81235
    Neil
    Member

    Hi all, I just joined,…

    … because I plugged in my vintage Small Clone (the pot says it’s a circa 1981 unit, a “Full Chorus”) after it sat for the past 23 years and I got nothing. 😥 I need help please!!

    This is a very nice site, by the way!

    I have pored over the site trying to find threads about similar issues to no avail. If I have missed a previous thread discussing the problem, please let me know which one and I’ll go there and try to figure it out.

    What I have found and read on this site seems to be mostly geared to newer Small Clone units. Elsewhere I’ve found stuff about passing signal, but its always dry, or Depth switch only working in the “Up” position. I did find a pretty good piece on “Axe Central” written by, “sharkdiver,” (Bill Kahle?), but I got lost with all his asterisks, which I think were bouncing back and forth between old and new units.

    Here are the symptoms of my particular unit:

    Fresh 9V
    Plug ” into Input, red LED turns on/off with switch.
    Play guitar through Small Clone into amp and get no sound.

    I can hear a faint chorus “wobble” effect on the input’s ambient noise with the light on, but no guitar at all in either on/off position. The faint “wobble” speeds up/down with the Rate pot. I think that’s a good sign,…

    I checked the guitar/amp. Everything works fine

    I have disassembled the unit and see nothing untoward inside. All wires/solder joints look good. No burned/smoked components. Input/output jacks all look like they should and make good contact according to my multimeter.

    As far as I can tell, this thing should work!

    I am relatively capable with a soldering iron, but I’m no electronics engineer. I’ve followed several tube amp mods (replacing surface mounted IC’s, lifting legs of filter caps etc.) to good results. Mouser e-mails me stuff,…

    Any “spiritual advice” you can lend would be greatly appreciated! :clap:

    Thanks much,

    Neil

    January 14, 2011 at 11:49 pm #113767
    KartoonHead
    Member

    Get prodding away with one of these; http://www.diyguitarist.com/PDF_Files/DIY-AudioTester.pdf

    January 15, 2011 at 12:42 am #113768
    The EH Man
    Moderator

    There’s an electrolytic capacitor just below the delay IC (SAD1024A or MN3007). When it’s bad you get a very weak chorus sound.

    January 15, 2011 at 3:49 pm #113780
    Neil
    Member

    Ron and Kartoonhead,

    Thanks for the speedy replies!

    Thanks, Kartoonhead, for the easy plan to make a test lead. I’ll have to source the 0.1uF 50V cap and make it.

    By the sounds of it, according to Ron, I’ll need to be getting another cap in there anyway. Gotta love one stop shopping,….

    Ron, is the cap you are referring to a 10uF 18V (Reeken?) blue, “can,” type? There are three on the board that I can see. They all look good from the outside.

    You said when it’s bad you get a weak chorus sound. While I am getting a weak chorus sound, I’m not getting any guitar signal at all, just the weak wobbling sound on whatever is coming through on the ether.

    I think I may have just had an, “Ah Ha” moment while I was looking at that cap through a loop ,… :freak: (<- what the cap saw) On the solder side of the board the legs of the cap may be touching the next resistor. The legs stick through the board and appear to be bent over. I’m not sure how that would have happened sitting in a box for years on end. Gremlins? I’ll test this find with my meter. If it’s shorted, I’m going to try lifting/cutting the legs in that area short and see if I get this to work. If that doesn’t do it I’ll build the audio tester and replace that cap (after I hear that I have identified the correct cap, please!). Any other advice gents? Like I said, I’m getting no signal at all,… Best Regards, Neil

    January 15, 2011 at 5:00 pm #113784
    Neil
    Member

    Neil again,…

    I just looked very carefully at the solder joints on the cap discussed in my previous post.

    It appears that they have been that way since the unit was manufactured. There is definitely solder joining the legs to the neighborng resistor on the backside of the board.

    As such, I did not cut/lift them, as they appear to be intentionally connected.

    Always open to advice.

    Thanks,

    Neil

    January 19, 2011 at 7:18 pm #109598
    Neil
    Member

    Kartoonhead and Ron,

    So, I made the audio tester and started probing around looking for where the signal craps out.

    I get signal up to pin 3 (1IN+) of the RC4558N op-amp, but that is as far as it goes (battery installed with switch/LED “on”).

    So far, my guess is the RC4558N op-amp is dead.

    In my search on this problem so far, I have seen no mention of the RC4558 op-amp going bad. Any advice please?

    From scouring the ‘Net for “RC4558N” I think I have found that a suitable replacement is Mouser PN: 595-RC4558P (supposedly the RC4558N made by TI, rather than Raytheon).

    I’d love to hear from you before I order/replace this part, as it’s surface mounted, so more difficult to replace than the socketed IC’s/op-amps,…

    Thanks much!

    Neil

    January 19, 2011 at 7:37 pm #108687
    The EH Man
    Moderator

    Check pin 8 of the 4558 with a voltmeter and see if there’s about 9vdc on it.

    January 19, 2011 at 7:45 pm #108688
    Neil
    Member

    Hey Ron, thanks for responding!
    Yep, I have batt. voltage on pin 8
    Neil

    January 19, 2011 at 8:44 pm #108707
    The EH Man
    Moderator

    You’ll probably need to replace the 4558.

    January 19, 2011 at 8:48 pm #108709
    Neil
    Member

    Thank you Ron!

    Shall I:
    1.) Post a reply to this thread when I install it and it works/doesn’t work?

    2.) Post a new thread giving the results?

    3.) Just shut up and play my guitar?

    All the best,

    Neil

    January 19, 2011 at 8:52 pm #89192
    The EH Man
    Moderator
    Quote:
    Thank you Ron!

    Shall I:
    1.) Post a reply to this thread when I install it and it works/doesn’t work?

    This one would be best.

    January 20, 2011 at 12:00 am #89199
    lerxst88
    Member

    are you sure your cable works? the guitar works?

    Might seem kind of trivial to ask but hey…I’ve done it!

    January 20, 2011 at 3:46 pm #113917
    Neil
    Member

    Thanks for the thought, lerxst88.

    Yes, I have an otherwise working system.

    You will see in the thread that Kartoonhead offered up a simple audio tester design, which I fabbed up and have been using for troubleshooting this unit. I’m sure that I’ll be using this handy tool again in the future, as I hang on to all my old gear (whats GAS without amassing a pile of gear, eh?).

    While I suppose you could use just about anything as a signal w/the audio tester, I have a cable tester that has a test tone function. I have been using that as a signal, which is a lot more convenient than plucking a string on an instrument and tryig to get back to the test point you are working on. Just a little hint for those of you who are even more electronically challenged than me ;) .

    As, “The EH Man,” said I should, I will post the results of my efforts after I replace the 4558 op-amp. I’ll order it today and hopefully get a chance to install it within a week’s time (no parts available locally,…)

    Best Regards,

    Neil

    January 20, 2011 at 9:04 pm #113923
    KartoonHead
    Member
    Quote:
    no parts available locally,…)

    Tell me about it, I have to order all of my electronics for building pedals from Germany XD

    January 21, 2011 at 10:32 pm #113939
    Neil
    Member

    It’s Fixed! :D

    Replacing the RC4558 op-amp solved the no signal (at all) problem.

    A big, “Thank You!” to, “The EH Man,” (a Big #1 response to you my man!), for helping me troubleshoot, diagnose and remedy the issue with my ’81 era Small Clone!

    And to Kartoonhead for “spiritual advice” and the handy audio test tool, I couldn’t have figured it out w/out it, or w/out both your help!

    A few notes,…

    I managed to source a MC4558CN op-amp from a local sound gear joint after all (OK, I’ll give ’em some props, it was Sound Source in Rochester NY). Their tech said that there would be no noticeable difference between the two op-amps.

    The original op-amp part number in my ‘Clone was a RC4558N. From what I was able to research, the RC4558P is the exact same op-amp, but just by a different manufacturer.

    I have an RC4558P on order,… just to get closer back to the OE spec components

    From what I can tell on the product data sheets, there are a few differences between the op-amps, but not much. The biggest thing that caught my eye was the voltage gain differences with the RC4558P being about 3dB higher than the MC4558CN. Perhaps The EH Man can shed some light on if there is/will be a noticeable difference between to two op-amps for this application?

    As I am going to be swapping the MC4558CN op-amp out for the RC4558P, I installed a socket so that I don’t have de-solder/re solder the parts and ravage the board any further (the traces are rather brittle on this old, brown, board,…).

    Thanks again!

    PLU,

    Neil

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