Warm Audio - TB12 Tone Beast ORANGE - No Signal

[callgrlmusic]

All,

friend of mine complained that his ToneBeast stopped working, and being that I'm the only one of his friends brave enough to peek under the hood, I've beeen asked to take a look. The TB-12 is essentially an outboard preamp with a few selectors for different types of capacitors, op-amps, input transformers, and the usual gain/hp/etc knobs and switches. In theory it's a very usable and cool box, and one could roll their own op-amps or transformers without much trouble if they wanted to.

So far I've:

1. visually inspected all capacitors for faults/leakage
2. cleaned all pots with Deoxit D5
3. tried using a known good mic, same cables, and a different outboard preamp into the same interface to rule out any of those things (it worked with the other preamp)
4. tried using both a known good dynamic mic and a good condenser (attempting to rule out phantom power issue)
5. used my multimeter to probe the actual power supply cord (showing 24v, as expected)
6. used my multimeter to probe the xlr connector with phantom power applied (assuming this should be 48v +/-4, but it's reading somewhere in the ballpark of 14v.)

I'm still getting no output. None at all, no matter what i do. To this device's credit, opening it up reveals, essentially, the world's most straightforward block diagram, which is cool; I tried calling Warm customer service and they really wanted me to send it in for repair and would not offer advanced troubleshooting over the phone. What would you do to troubleshoot from here?

 

[mjrippe]

Nice work so far and good photos. Check the voltages on the ribbon cable coming out of the power supply. You should find +/- 15VDC and +48VDC, the other pin is ground of course.

 

[kags]

did you unplug and reseat all the Molex connectors? Also pull and reseat the opamps? That unit is prob 10-12 years old or so and could use some love.

 

[callgrlmusic]

Nice work so far and good photos. Check the voltages on the ribbon cable coming out of the power supply. You should find +/- 15VDC and +48VDC, the other pin is ground of course.

thank you—not to sound very ignorant, but how would i be able to tell how these are the voltages i should have?
left to right, if i put my negative probe on the first pin and positive on the second, third, and fourth pins, respectively, i’m getting +4v, -13v, -13v. that seems weird, right?

 

[callgrlmusic]

did you unplug and reseat all the Molex connectors? Also pull and reseat the opamps? That unit is prob 10-12 years old or so and could use some love.

yeah, no dice.

 

[callgrlmusic]

another clue: when i switch transformers back and forth or switch op-amps back and forth, using the selector pots, i get some kind of pop in my input meter but no long-term audio signal. seems bad>?

 

[NoisyIndividual]

thank you—not to sound very ignorant, but how would i be able to tell how these are the voltages i should have? View attachment 144180
left to right, if i put my negative probe on the first pin and positive on the second, third, and fourth pins, respectively, i’m getting +4v, -13v, -13v. that seems weird, right?

You are correct, this is your problem.

There is probably something wrong with the PSU.

It may be trying to start, producing some voltages, then shutting down and trying again.
They kind of do that.

 

[scott2000]

left to right, if i put my negative probe on the first pin and positive on the second, third, and fourth pins, respectively, i’m getting +4v, -13v, -13v

the first pin is ground I'm assuming?
btw...visual inspection of caps is only useful for just that. Caps can still be useless and look good. especially the chang chongs and off brands...etc...
not saying that's the case...just saying

 

[NoisyIndividual]

It doesn't really matter if the first pin is ground or not.

There is no way by these measurements you have a 5v and +/- 15v supply present.

 

[NoisyIndividual]

I would check for a shorted diode or bad cap, particularly on the +15v rail which appears to be absent.

 

[callgrlmusic]

I would check for a shorted diode or bad cap, particularly on the +15v rail which appears to be absent.

not being sure what to do next, i took the power supply out and started testing diodes and resistors.

all resistors tested within spec—

my next question is three parts:

a. any idea whether d9 and d10 are standard diodes or zeners? how would i find this out?

b. i’m getting a voltage drop of 0.4v in one direction and 0.7v in the other direction on BOTH of these diodes. does this mean they’re failing, and if so, is there anything else on this board that would’ve caused that directly?

c. if both a and b above are behaving normally, what would be my next step?

 

[NoisyIndividual]

0.7v usually indicates a Zener.
Diodes usually 0.6v ballpark.

My usual approach would be to replace all the electrolytic capacitors.
The originals are usually ****, so this is generally a good plan and not really very costly.
Provide you buy your parts from a reputable vendor and not from Ebay or Ali, in which case you will end up with the same **** power supply.

Check all the diodes, they almost always go short, not open.

Do this, and you will then have a stonking new power supply, much better than the original, which was probably manufactured for $3

 

[sheshotel]

the first pin is ground I'm assuming?
btw...visual inspection of caps is only useful for just that. Caps can still be useless and look good. especially the chang chongs and off brands...etc...
not saying that's the case...just saying

Really hoping that wasn’t a racist jab? especially considering recent events in the U.S.

 

[scott2000]

Really hoping that wasn’t a racist jab? especially considering recent events in the U.S.

grow up..
then visit badcaps forum or something

 

[callgrlmusic]

0.7v usually indicates a Zener.
Diodes usually 0.6v ballpark.

My usual approach would be to replace all the electrolytic capacitors.
The originals are usually ****, so this is generally a good plan and not really very costly.
Provide you buy your parts from a reputable vendor and not from Ebay or Ali, in which case you will end up with the same **** power supply.

Check all the diodes, they almost always go short, not open.

Do this, and you will then have a stonking new power supply, much better than the original, which was probably manufactured for $3

not a bad idea.

is it worth looking at the MOSFETs at all? can any failures there cause other components to fail? how likely is there to be a problem there?

 

[NoisyIndividual]

No. The Mosfets will fail short, just as the diodes will do.

this makes things much easier.


Replace all the ***** caps and then go from there.
Chances are that will sort it.

 

[callgrlmusic]

i'll report back. thank you all for the help, especially NoisyIndividual

 

[mjrippe]

Just to clarify a couple things...the diodes are not zeners, they are standard diodes used for rectifying the AC input. And the three legged devices with heatsinks are voltage regulators, not MOSFETs. If a recap fails to bring it back to life, the regulators would be next on the list.

 

[NoisyIndividual]

Hang on a sec, I've just realised the power supply input is a DC jack.

So for this supply to work you probably need an AC adaptor, not your typical DC one.


The AC adaptor will be capable of generating plus and minus supplies a DC adaptor won't.

 

[NoisyIndividual]

Scratch that, seems you clarified you have an AC input.