Here's a head-scratcher...

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GaryMadore
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Re: Here's a head-scratcher...

Post by GaryMadore » Thu Mar 02, 2017 8:24 pm

dalrymple wrote:Fendre
Dink! ;)

GaryMadore
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Re: Here's a head-scratcher...

Post by GaryMadore » Fri Mar 03, 2017 8:45 pm

So....

The good news is that It isn't the Encoder, Processor, Midi, or USB/Headphones boards: I swapped in the ones from my 120 and there was no change.

The bad news is that It isn't the Encoder, Processor, Midi, or USB/Headphones boards.

I borrowed my daughter's stethoscope to try out the ol' mechanic's trick for isolating noises and was surprised to hear a lot of noise on (in?) the chassis. Flipping it over, I put the stethoscope on the side of the power transformer and heard a ton of hum. Loud, buzzy hum.

I had it apart today and noticed something that I never would have noticed if I hadn't taken the T120 and V30 apart and put 'em back together so many times: On the T60, someone had plugged the blue primary onto the XFMR HOT connector and the black onto the XFMR NEUTRAL connector, which is the opposite of convention. I didnt think it should matter much (the polarity) but I figured that the noisy PT and the swapped leads couldn't be a coincidence and had to be the problem. Nope. Swapped them and the problem was still there.

I went over the grounding and it's all good. Removed and replugged all the connectors - all good.

So this has me wondering if the power transformer is the culprit.

The only other thing it could be is the power board and I can't swap in a replacement, as it's waaaaaaay different from all of my others. Unless anyone can tell me if pulling tubes 1 & 3 from the T120's board and dropping it into the T60 for a test is both safe and recommended (?)

If someone with more knowledge than me (that'd be everyone here) can tell me if the symtoms point to the power transformer (buzzy hum through the speaker, happens with nothing plugged in to the input, the noise follows the volume knob), I'd be very very appreciative.

This one has me vexed. But as long as I have the tubescreamer active it's quiet... so I can live with it.

I'd take it to the techs at Spaceman Music here in town (ye olde school kinda techs) but just the diagnostics would cost what I paid for this amp (you don't wanna know what I paid for it) so I'm not sure I'll bother.

Thanks,

Cheers!

Gary

GaryMadore
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Re: Here's a head-scratcher...

Post by GaryMadore » Sat Mar 04, 2017 9:40 am

Here are a couple of audio files recorded with my laptop's built-in mic. The first is a quick 5 second sample and the second is a 24 second sample of the noise as I run through all the stompboxes for 2 seconds each.

Base noise:
AmpNoise1.mp3
(118.02 KiB) Downloaded 195 times
2 seconds each of the stompboxes in order: Ring Modulator, Auto Wah, Analog Flange, MOG (octave generator), Analog Phase, Tube Screamer, Bypass, XR Wild, X Boost, Fuzz, BC Chorus, and Squeeze (compressor).

As you you can see (er, hear), the noise is being modified by the stomboxes: It's wah-ing, flanging, chorusing, etc.
AmpNoise2.mp3
(565.51 KiB) Downloaded 194 times
Also probably important, the largest effect on the noise comes courtesy of the Pre Gain control. At Level 4 and below there's no remarkable noise, and it increases exponentially at 5 through 7.

I've worn a bald spot on my melon with all this head-scratching...

Cheers!

Gary

dalrymple
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Re: Here's a head-scratcher...

Post by dalrymple » Sat Mar 04, 2017 10:32 am

OK, I'm pretty sure you are picking up alien transmissions based on the second sample. I played that backwards and it says Paul is OLD!!! In Cardasian.
Time to boost the power and tell 'em to shutup. Damned Gremlins.
Jeez.
Dalrymple

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j_fury68
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Re: Here's a head-scratcher...

Post by j_fury68 » Sat Mar 04, 2017 4:08 pm

Have you tried swapping the DSP? The one from the 30 should work. You just can't plug in the USB. I've got a 15 that makes noise you would swear was a blown speaker, but it's not. Did all the same board swapping, speaker swapping too, to no avail. It's DSP is "hinky", or wonky as I like to say. :lol:
:arrow: Peavey HP Special FT in Blue Moon Burst, Vypyr 30 with Effects Loop, Zoom G5, Vypyr Pro 100.

GaryMadore
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Re: Here's a head-scratcher...

Post by GaryMadore » Sat Mar 04, 2017 9:36 pm

j_fury68 wrote:Have you tried swapping the DSP? The one from the 30 should work. You just can't plug in the USB. I've got a 15 that makes noise you would swear was a blown speaker, but it's not. Did all the same board swapping, speaker swapping too, to no avail. It's DSP is "hinky", or wonky as I like to say. :lol:
Yep: Swapped in the encoder board, DSP board, midi board, headphones/USB board, and input jack from my Tube 120 - no joy.

The only board I haven't swapped yet is the power board and that's because mine (in the 120) is so radically modified that I'd be afraid to take it out again ;)

It's all very vexing.

Cheers!

Gary

dalrymple
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Re: Here's a head-scratcher...

Post by dalrymple » Sun Mar 05, 2017 8:29 am

Hmmmm. Sadly, the pronouncement of hinkey may just be accurate. Sometimes amps have issues even experienced techs have difficulty pinning down.
Sometimes they wont even hazard a guess. Is it playable, or just unacceptable? I know your expectation is perfection, but can you live with the reality of what it presents?
Would a 15 year old give a rats ass?
See where I'm going with this one? You may have no use for it as it sits, but would someone else?
Try to salvage what $ you might by not throwing good $ after bad. If it's hinkey.
Just sayin'.
Dalrymple

GaryMadore
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Re: Here's a head-scratcher...

Post by GaryMadore » Sun Mar 05, 2017 10:17 am

dalrymple wrote:Is it playable, or just unacceptable?
It's totally playable, especially given that I love me some Fendre (grin) cleans: With the pre-gain below 5 or so, the hum is barely noticeable - and when playing, the guitar drowns it out.

I can live with it but, well, you know me....

The thing about hink, though, is that *something* has to cause it. Once tracked down, the fix is easy (not always cheap, but definitely easy).

This sumbitch is laughing at me though :-/

Gonna try the transformers from the '120 in it today. If that's not it, that only leaves the power PCB... everything else will have been swapped out.

I hates me some hink.

Cheers!

Gary

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wmjones
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Re: Here's a head-scratcher...

Post by wmjones » Sun Mar 05, 2017 2:07 pm

GaryMadore wrote:[quote="something has to cause it.
[/quote]

I agree with you, something has to cause it. One more thing I would try is to reverse the speaker leads. One more thing, have you checked to see if all the cables connecting the boards (components) are good? If you are like me you will not be satisfied until you find the answer and able to fix it. Don't give up on the problem, The worse case scenario is that you will increase your knowledge about amps.
8) HAPPY DAYS:

GaryMadore
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Re: Here's a head-scratcher...

Post by GaryMadore » Sun Mar 05, 2017 2:36 pm

wmjones wrote:I agree with you, something has to cause it. One more thing I would try is to reverse the speaker leads. One more thing, have you checked to see if all the cables connecting the boards (components) are good? If you are like me you will not be satisfied until you find the answer and able to fix it. Don't give up on the problem, The worse case scenario is that you will increase your knowledge about amps.
I've had the leads and ribbon cables all on and off, but haven't swapped anything (except for the PT primaries, which were backwards (though that shouldn't really make a difference). I'll give it a go, thanks.

I like your sunny outlook. Kinda ;)

Cheers!

Gary

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Re: Here's a head-scratcher...

Post by GaryMadore » Thu Mar 09, 2017 7:35 pm

Did some more diagnostics tonight. Maybe something here will ring a bell with someone.

I checked out the power transformer (because it was buzzing) and got the following readings:

Output:

Red secondaries: 375V
Orange secondaries: 35V
Green secondariez: 8.4V
Yellow secondaries: 6.3V

Resistance (all leads disconnected):

Chassis to Primary Hot - Infinite
Chassis to Primary Neutral - Infinite
Across the Primaries - 2.9 ohms
Across Secondary 6.3V Tap (Yellows) - 0.4 ohms
Across Secondary 375 V Tap (Reds) - 37.9 ohms
Across Secondary 35 V Tap (Oranges) - 5.9 ohms
Across Secondary 8.4 V Tap (Greens) - 0.7 ohms

I haven't found any info yet to determine if those voltages are within spec, but I *think* the resistance readings are in the ballpark for a serviceable power transformer.

I started measuring individual components but quickly lost interest. Some resistors were a little odd:

R21 supposed to be 220K is 70K
R13 supposed to be 220K climbs slowly to 190K
R14 supposed to be 220K flashes 180-190K then goes to infinite

Also oddly, R21 is a big, ugly green thing with no markings on it and it doesn't look like anything else on the board. It's glued in place, though, with the same white goop they used everywhere else so I have to believe that it's original. Sure doesn't look it, though. It's in the circuit that takes the rectified HV @ 395VDC. It's also tied to B++ and Screen drops.

I reflowed the solder on some joints that didn't look spectacular and tested continuity from all of the socket pins to the solder blobs on the other side of the board: all good.

After giving up for the night and bolting it back together, I fired it up - no change (sigh)

But I did notice one thing: With the stompboxes on Bypass and cycling through the amps, I found that all of the amps on the left side of the dial (XXX, JSX, 6505, Rec, K-Stein, Dzl) were all noisy in dirty/red mode but quiet in clean/green mode. Conversely, all of the amps on the right side of the dial (Twn, Dlx, Plexi, Brit, B-Cat, Classic) were quiet in dirty/red mode and noisy in clean/green mode.

I remember reading something similar somewhere sometime, but I can't for the life of me find it again. One would suspect the encoder board, but I've changed both the Encoder and DSP boards with no joy - the noise remained.

Also, I've read that if the noise follows the volume, then it's being injected somewhere before the volume control. If the same holds true for the stompbox dial, etc., then it looks like it's happening before it, and so maybe before the encoder/DSP?

Sign me "Stil Vexed in the Still Frozen North."

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