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FDP Forum / Guitar Mods, Repairs, and Projects / Help me diagnose a complete loss of signal?

vomer
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Broke Down

in the Brassicas
Mar 15th, 2017 06:14 PM   Edit   Profile   Print Topic   Search Topic

I have a friend's strat in at the moment, with intermittent complete loss of pickup sound across all pickups in all switch positions. No obvious aggravating factors, waggling wires about etc, and everything looks OK.

I'm wondering if this might help the diagnosis: when the signal cuts out, 'normal' hum is still present, which as usual goes away on touching the strings. Does this help indicate whether the hot signal path is either broken or shorting to ground, or does it not help the diagnosis?

The switch is one of the boxed-in YM-30's and I don't know if they can be opened. If not I'll replace it and re-flow all the connections. Any suggestions as always gratefully received.

littleuch
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Florida

Mar 15th, 2017 06:34 PM   Edit   Profile   Print Topic   Search Topic

I would start at the input jack. But what do I know.

Peegoo
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The spotlight

looks like a prison break
Mar 15th, 2017 07:54 PM   Edit   Profile   Print Topic   Search Topic

The symptoms indicate a short of the signal to ground, inside the guitar. Check the output jack first: make sure the tip of the plug, when inserted into the jack, is not making contact with shielding in the jack cavity. If that checks okay, continue through the circuit with a meter until you find the short.

wrnchbndr
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New Jersey

I'm back with the otters again
Mar 15th, 2017 08:41 PM   Edit   Profile   Print Topic   Search Topic

#1 cause is a broken wire on the output jack due to someone trying to tighten a loose jack and twisting the wires so tight that they break. Some strats have shielding paint in the control cavity and a pot that comes loose can rotate either shorting the signal wire to ground or breaking the wire(s). Pots and pickups very rarely die completely. I've only seen one pot totally die.
Sounds kinda dumb and obvious but always verify the amp and instrument cable first.

littleuch
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Florida

Mar 15th, 2017 09:18 PM   Edit   Profile   Print Topic   Search Topic

See, I told you...what do I know.

Calling the output jack an input jack. SMH.

vomer
Contributing Member
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Broke Down

in the Brassicas
Mar 16th, 2017 03:16 AM   Edit   Profile   Print Topic   Search Topic

Thanks guys. Yes, I've already checked the jack and will try the circuit testing again later. I had previously tried but nothing showed up, the joys of an intermittent fault. That's why I said I'd probably just re-flow everything.

Does anyone know if the YM-30's can be opened?

SonicBlue

Sunbury-on-Thames

Mar 16th, 2017 07:56 AM   Edit   Profile   Print Topic   Search Topic

If the cavities are shielded check for a control pot twisting and shorting a lug to ground.

If that isn't the case, test at the halfway point.

Where the pickup selector side of the five way switch is jumpered across to the tone side, unsolder the jumper wire and wire the p/u selector output straight to the output jack, bypassing all the tone and volume stuff. Don't forget to disconnect the existing output wire from the jack. Run it like that for a while and see if the problem goes away. If it does, the fault lies between the 'input' to the tone selector side of the switch and the jack. If it doesn't, the problem is either pickup wiring or the switch.

Look carefully for any sign or possibility of a switch lug touching any shielding when it's all bolted up too.

Bubbalou

USA

THE LOW END OF UPPER TEJAS
Mar 16th, 2017 08:52 AM   Edit   Profile   Print Topic   Search Topic

"The symptoms indicate a short of the signal to ground, inside the guitar. "

I mean no disrespect as you are one of the smartest here but in my experience a signal shorted to ground would be dead quiet while an open would cause hum.

Te 52

Laws of Physics

strictly enforced
Mar 16th, 2017 11:11 AM   Edit   Profile   Print Topic   Search Topic

Yes, sounds like loss of ground. I'd take an ohmmeter and check from the metal of the jack on the outside of the guitar to the ground solder lug on the output jack. If that checks out, check from that solder lug to everywhere inside the guitar that's supposed to be grounded.

amphead4

Cincinnati, USA

Mar 16th, 2017 11:21 AM   Edit   Profile   Print Topic   Search Topic

I think not a shorted signal to ground for the same reason as Bubbalou gave.

I don't suspect a loss of ground because that typically results in massive hum, not normal hum.

I think something carrying the signal has an intermittent open. This would be between the switch and the jack since it affects all three pickups the same.

Bad switch, bad volume pot, bad jack, bad wiring, etc.

Peegoo
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The spotlight

looks like a prison break
Mar 16th, 2017 03:11 PM   Edit   Profile   Print Topic   Search Topic

Bubbalou, no offense taken.

I suspect a short to the shielding paint based on the symptoms. If it were a loss of ground, chances are the hum would not disappear when touching the strings.

Could be one of several possible causes...

uncle stack-knob
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united kingdom

Mar 18th, 2017 05:43 AM   Edit   Profile   Print Topic   Search Topic

I would change out the YM-30 switch anyway,as they are unreliable and rubbishy.

Stack-Knob.

vomer
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Broke Down

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Mar 18th, 2017 11:48 AM   Edit   Profile   Print Topic   Search Topic

Sorry, I just realised YM-50 not 30 but I assume they're the same only 5-way.

Well I could not reproduce the fault at all, all connections are good, took apart the volume pot, all OK, no possible shorts to the shielding I can see, so I haven't got any further with a diagnosis.

Except I did find that the YM switch does come apart easily. Two little screws on one side. It was dirty, pic below shows the build up of corrosion on the little spring, and the black smear on the yellow of the wafer is where I ran my finger over the tracks and that's what came off them. So maybe some crud on the tracks, (© my next album title! :-)), or the little copper contacts were losing contact. I had heard these switches weren't that good, but it does seem quite solidly built and has lasted thirty years. But yes Stack-Knob, I'll replace it when the new ones arrive, I don't want this uncertainty again with this guitar.

Thanks for everyone's comments.

Inside a YM-50 MIJ strat switch

Mick Reid
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Australia

American-made in Oz!!
Mar 18th, 2017 04:54 PM   Edit   Profile   Print Topic   Search Topic

So are you saying the guitar/switch work properly after cleaning the contacts?

vomer
Contributing Member
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Broke Down

in the Brassicas
Mar 18th, 2017 05:14 PM   Edit   Profile   Print Topic   Search Topic

Mick, I don't know because the problem is, it was mostly working perfectly anyway (no crackles, and clear tones) before I took the switch apart... I've had the guitar on the bench for a couple of days and since I got it it's only not worked for a couple of minutes, and it's cut out and come back to life with no obvious input from me. Because it was previously totally OK when it was working, I won't know if cleaning the switch has made a difference until it cuts out again, if it ever does.

(This message was last edited by vomer at 07:19 PM, Mar 18th, 2017)

Mick Reid
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Australia

American-made in Oz!!
Mar 18th, 2017 11:13 PM   Edit   Profile   Print Topic   Search Topic

"...and it's cut out and come back to life with no obvious input from me."

I hate it when that happens!
Hope you successfully find the culprit.


hushnel
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North Florida

A Friend of Bill W.
Mar 19th, 2017 10:52 AM   Edit   Profile   Print Topic   Search Topic

Intermittent problems are a pain to run down, a lot of times it's a cold solder. Just putting the meter probes on the failure can establish a connection. Still simpler in point to point than circuit boards, transistors and chips.

vomer
Contributing Member
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Broke Down

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Apr 23rd, 2017 03:34 PM   Edit   Profile   Print Topic   Search Topic

I had a look at that YM-50 switch again in a spare moment. The switch looks sturdy and well made, so I was wondering why they were unreliable. I found something which might account for that. Where the input/output connectors meet the wafer they are eyelets, riveted through the wafer. But they aren't soldered to the tracks. So I assume a possible source of bad connections, dirt and corrosion, etc. Just thought I'd mention it in case anyone finds themselves having the same intermittent problem with one of these. It's too easy to assume the switch is OK just by looking at it and continuity testing it.

Peegoo
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The spotlight

looks like a prison break
Apr 23rd, 2017 03:45 PM   Edit   Profile   Print Topic   Search Topic

Could be. It's the ol' dissimilar metal/Galvanic issue.

FDP Forum / Guitar Mods, Repairs, and Projects / Help me diagnose a complete loss of signal?




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