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Thread: Vintage fender sidekick tube 20r 1986 model burnt resistors! R57 R58

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    Vintage fender sidekick tube 20r 1986 model burnt resistors! R57 R58

    Good day!

    So I accidentally plugged my amp to a 110V power outlet.

    The amp required 100V ONLY!

    It worked (for a while) then smoke came out from the back and the volume dropped down to barely audible.

    I opened the amp. Checked the fuse, tubes, caps, etc.

    I found out that the resistors R57 and R58 were burnt.


    Problem is, I don't know the values of these two Resistors. Can't rely on the color coding either because they turned black. I can't replace them without their values.

    I searched the internet for Schematics but found nothing.
    I emailed fender but still they have nothing.

    Fender:

    Jeremy Ault (Fender)

    May 22, 12:41 MST

    It's for us to say what the values would be since we lack the proper documentation. Unfortunately, since this amp was produced around a transitional period when CBS sold Fender in the Mid 1980s none of that information was transferred and we were not able to reacquire it while we rebuilt the company. I apologize we could not be of more assistance

    Jeremy Ault

    Representative, Consumer Relations /U.S. Direct
    Sales

    Fender Musical Instruments Corp.
    17600 N. Perimeter Drive, Suite 100
    Scottsdale, AZ 85255
    Telephone: 480-845-5140
    Fax: 480-367-5262


    I'm not an amp expert and I badly need help. Thank you!

    All photos are in here : https://drive.google.com/open?id=1Ng...KWqcuhH7YRlT4A



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    Stray Cap DrGonz78's Avatar
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    To me it looks like those burnt up resistors are probably dropping resistors for the lower voltage preamp supply. D10 & D9 appear to burnt up a bit too and it would not surprise me if those diodes test open or shorted. D10 & D9 most likely are 15v or 16v zener diodes that connect to R57 & R58 that regulate the, typically, -/+15v preamp voltages. Now did they burn up when IC's went bad down stream and pulled too much current? Those resistors could be 1 watt with a resistance value of 220-1000 ohms, but it is very difficult to say for certain without knowing what the higher voltage is that it is dropping down. Hopefully you may find someone with this amp that is willing to take pictures of the inside of the amp. Still there could be other components damaged in the amp and simply replacing those components might not fully fix the amp. I would read up on light bulb limiters so you can build one if you decide to go about fixing this amp.

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    Supporting Member Randall's Avatar
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    Where are you located where you have the choice of 100 or 110v operation?

    Is it me, or does +10v seem like not enough to smoke an amp?

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    It's weird, because it WAS working fine.....

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    Supporting Member The Dude's Avatar
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    Agree with both. I don't think 10V would kill it. And, I'm betting something is shorted- maybe zeners. I know the resistors are burnt, but did you try to measure them (at least the least burnt one)? Maybe that would give us a clue- if not value, maybe at least an upper resistance limit.

    P.S. When did I get old enough that a 1986 amp was considered vintage?

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Randall View Post
    Where are you located where you have the choice of 100 or 110v operation?

    Is it me, or does +10v seem like not enough to smoke an amp?
    Japan I believe uses 100v.

    nosaj

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by nosaj View Post
    Japan I believe uses 100v.

    nosaj
    And I can't recall any other nation or area that uses 100 VAC as standard power. There has been a butt load of "grey market" gear shipped from there since the 1980's. It was such a problem I recall Yamaha refused warranty service on popular DX7 keyboards that had been acquired thru grey market channels. 110 yes seems hardly enough to worry, but we're mostly 120V in the USA, with some locations sporting line voltage closer to 130 - that would be enough to raise hob with a 100V rated item. Imagine plugging your standard 120V amp into 140-150V. That would let the smoke out of the wires right quick.

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    Old Timer olddawg's Avatar
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    I would bet that’s a Japan model. I used to work on a lot of greymarket stuff in the 80s... I’ve rarely seen Japan market stuff that wouldn’t work in the USA.. You can get problems over time with heat dissipation. Usually the only difference between a USA model is the transformer. Can you look at the schematic of a similar USA amp? Btw.. that response sounds like bs..

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by olddawg View Post
    that response sounds like bs..
    Indeed. Either Fender is being polite about not wanting to deal with an obvious grey market piece, or doesn't want to waste time supplying info on a 30+ year old amp that would be sold with a DNR notice to repair centers in the current day. Either way, an old amp fixed equals a new amp not sold, from the point of view of any company's marketing executive. Sounds harsh but that's bizness. Fender executives must be grinding their teeth into powder thinking about the amps made 1950-1990.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Leo_Gnardo View Post
    Indeed. Either Fender is being polite about not wanting to deal with an obvious grey market piece, or doesn't want to waste time supplying info on a 30+ year old amp that would be sold with a DNR notice to repair centers in the current day. Either way, an old amp fixed equals a new amp not sold, from the point of view of any company's marketing executive. Sounds harsh but that's bizness. Fender executives must be grinding their teeth into powder thinking about the amps made 1950-1990.
    Well a search turns up no schematic for the 20r but we get the 15, 25, 35, 65 here https://music-electronics-forum.com/...ad.php?t=33010
    nosaj

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    Supporting Member Randall's Avatar
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    "P.S. When did I get old enough that a 1986 amp was considered vintage?"

    You took the words right out of my brain.

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    It's weird, because it WAS working fine.....

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Randall View Post
    "P.S. When did I get old enough that a 1986 amp was considered vintage?"

    You took the words right out of my brain.
    Sometimes when I'm writing a check (how 20th century...) I have to catch myself before writing 1980-something onto the date area. Geeze, seems like yesterday. All this new-fangled stuff sure is amazin' ! I gotta catch up with the kids and get me a pocket computer.

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    Try contacting Elk Electronic Industries instead. After all, that is the company who manufactured these amps for Fender Japan, Ltd., which - BTW - was entirely different business entity than the Fender Musical Instruments Corp. (FMIC) established in 1985 when CBS sold the Fender trademark and product inventory to some of the company's former executives and a bunch of investors. Yes, the trademark and product inventory. Not any of the factories, and even the product inventory was largely consisting of the cheap Japanese-made products.

    Fender Japan, Ltd. was established few years before any of this, in 1981 while Fender was still in CBS ownership. Fender executives simply realized they could not compete with cheap Japanese-made clones of Fender products flooding the markets. And when you can't beat them, you join them. Fender Japan was a joint venture with Kanda Shokai Corp. and Yamano Gakki, two big names in Japanese retail and wholesale business. The business model was basically based around finding various "OEM" manufacturers (Elk being the most prominent one) that could produce cheap products carrying the Fender trademark. They started with guitars and then expanded to amps producing series such as the "Sidekick", "Squier", "R.A.D.", "FAT", and et cetera. You know, the "cheap" stuff. Some of these Fender products were never even imported outside Japan.

    No, I don't find it at all hard to believe that FMIC didn't receveive all technical literature and IP related to each and every product that Fender Japan, Ltd. had "manufactured". Why would have they? The companies were largely independent business entities and FMIC had merely bought a trademark and bunch of old import products. Besides Fender Japan largely just contracted production of Fender products to third parties.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by teemuk View Post
    Try contacting Elk Electronic Industries instead. After all, that is the company who manufactured these amps for Fender Japan, Ltd., which - BTW - was entirely different business entity than the Fender Musical Instruments Corp. (FMIC) established in 1985 when CBS sold the Fender trademark and product inventory to some of the company's former executives and a bunch of investors. Yes, the trademark and product inventory. Not any of the factories, and even the product inventory was largely consisting of the cheap Japanese-made products.

    Fender Japan, Ltd. was established few years before any of this, in 1981 while Fender was still in CBS ownership. Fender executives simply realized they could not compete with cheap Japanese-made clones of Fender products flooding the markets. And when you can't beat them, you join them. Fender Japan was a joint venture with Kanda Shokai Corp. and Yamano Gakki, two big names in Japanese retail and wholesale business. The business model was basically based around finding various "OEM" manufacturers (Elk being the most prominent one) that could produce cheap products carrying the Fender trademark. They started with guitars and then expanded to amps producing series such as the "Sidekick", "Squier", "R.A.D.", "FAT", and et cetera. You know, the "cheap" stuff. Some of these Fender products were never even imported outside Japan.

    No, I don't find it at all hard to believe that FMIC didn't receveive all technical literature and IP related to each and every product that Fender Japan, Ltd. had "manufactured". Why would have they? The companies were largely independent business entities and FMIC had merely bought a trademark and bunch of old import products. Besides Fender Japan largely just contracted production of Fender products to third parties.
    Excellent information there teemuk, thanks for sharing.

    nosaj

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    I was born 1997. so for me, 1986 is quite vintage.

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    I'm in the Philippines. Got this amp from U.S.A

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    Don't forget the joker g1's Avatar
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    If it specifies 100V operation, it must have been originally from Japan.
    Did you try measuring the resistance of those resistors you removed?

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    ...And if you sketch out the circuit(s) from which those resistors are from it might help to determine their component values. If not exactly, then at least a close-enough values.

    Sometimes you simply have to live with the fact that no technical documentation is available. It's a basic mid 1980's amp design, how hard can it be?

    They seem to be in close vicinity to power supply circuit and what looks like either power amp or a regulator IC. Part of the regulator or voltage dropping circuit of the supply perhaps? What is the power amp or regulator IC, and could its datasheet perhaps provide some clues about involved circuitry? Where are the circuit board tracks running from those resistors?
    Do you -really- need a schematic for this? I understand it can be a convenience but for fixing this thing... do you really need it?

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    Don't forget the joker g1's Avatar
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    It's good that Teemu mentioned these being from the same origin as the R.A.D. & H.O.T. Those schematics are available.

    neilemborgo7, are there numbers on the power transformer that can help us match this up to another schematic?

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by nosaj View Post
    Well a search turns up no schematic for the 20r but we get the 15, 25, 35, 65 here https://music-electronics-forum.com/...ad.php?t=33010
    nosaj
    It's good that Teemu mentioned these being from the same origin as the R.A.D. & H.O.T. Those schematics are available.
    Sadly none of those applies.
    Those are all transistor amps, while this one is the very odd TUBE one.

    So unusual that I didn´t know they even *existed* , go figure.

    Did anybody actually read thread title and look at amp picture?

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    Master Destroyer nosaj's Avatar
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    Can you give us a pic of the whole PCB and the back side of the amp please?

    Thanks,
    nosaj

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    Don't forget the joker g1's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Sadly none of those applies.
    Those are all transistor amps, while this one is the very odd TUBE one.

    So unusual that I didn´t know they even *existed* , go figure.

    Did anybody actually read thread title and look at amp picture?
    I looked at it, and the board pics. I could only see a preamp tube socket so I figured maybe it just has a single preamp tube. Regardless, the burnt resistors are around a couple zeners and typical +/-15V rail size caps, so I figured the LV supplies might be the same.
    But you have a good point, the transformer won't match any of the others because it will have a HV winding.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by g1 View Post
    I looked at it, and the board pics. I could only see a preamp tube socket so I figured maybe it just has a single preamp tube. Regardless, the burnt resistors are around a couple zeners and typical +/-15V rail size caps, so I figured the LV supplies might be the same.
    But you have a good point, the transformer won't match any of the others because it will have a HV winding.
    only close thing I can find and no schematic. is the sidekick tube 30r 2 preamp tubes and a solidstate rearend.https://www.radiomuseum.org/r/fender..._tube_30r.html
    nosaj

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by nosaj View Post
    only close thing I can find and no schematic. is the sidekick tube 30r 2 preamp tubes and a solidstate rearend.https://www.radiomuseum.org/r/fender..._tube_30r.html
    nosaj
    Interesting.
    Let´s wait for a few closeups covering the full amp to start guessing with at least some data.

    What I find REAL weird is that power IC shown not only is not attached to a heat sink, but it works as heat sink for a TO220 transistor

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    Supporting Member Jazz P Bass's Avatar
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    That output IC may be the HA1388.
    HA1388.pdf

    Here is a crop of the 25R power supply.
    Sidekick 25 Reverb Pwr Supply.pdf
    Particularly the 15 Vdc supply.
    It shouldn't be that different.

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    https://drive.google.com/drive/folde...GtWTc95ImPo0az

    Sorry for this very late reply. Here some more pics of the amp. I hope you can help me.

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    Supporting Member The Dude's Avatar
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    Quote Originally Posted by g1 View Post
    ......Did you try measuring the resistance of those resistors you removed?
    ^^^^^^ I'll go back to this. Often resistors darken, but don't change value much. Measurements might at least get us in the ballpark.

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