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tertiumsquid

Variax 300 Repair (no output)

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Just got a non-working Variax 300 yesterday, no sound output. There’s honestly not a lot of info out there on repairing these things, so while I'm diagnosing the issue I'll post updates, to try and help others in repairing their instrument.  Personally I'd rather attempt board-level repair rather than swapping out the whole board, as I’m a cheapskate. 

 

I’m getting correct supply voltage into all the chips, and I've spent a bit of time tracing some signals. Audio passes properly from the piezo input through the op-amps to the ADC, and the audio path from the DAC through to the output works. The DAC's are receiving the 10mhz master clock signal, but I'm not getting anything from the digital audio output.

 

I noticed while tracing signals that I have a burnt resistor in the upper left near the ribbon connector, R48. It measures 18 ohms, but I can't read it to tell what it's supposed to be. That resistor connects directly through the various cables to the network jack (pin 5), so I'm led to believe that the guitar was plugged into something else rather than the Variax input on a Pod. Possibly the FBV input of something.  Also I read a forum post on here where someone mentioned that one of the inductors tends to fry when plugging into a FBV input, but my inductors are ok.

 

Not sure how the guitar works, but it's possible the guitar thinks it's in some sort of mode that disables audio output through the analog jack, but that's just speculation.  I don't currently own and Pod products, but a friend has a Pod HD Pro, so I’m going to see if I can flash the firmware through that.  Any suggestions of common failures or stupid things I’ve probably overlooked are welcome.

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On 11/24/2018 at 9:55 AM, soundog said:

Is this useful to you?

 

 

 

Nice resource... thanks!

 

OP: Based on that resource, R46 and R48 should be the same value... keep in mind you can't test components in a circuit without getting unpredictable results. That resistor looks gone to me... even if it still had any life, I'd be replacing it. 

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Good detective work so far! If you don't already have some, I'd get a short length of low temp alloy designed for surface mount removal, at a minimum. Something like this.

 

 

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On 11/24/2018 at 9:55 AM, soundog said:

Is this useful to you?

 

 

 

Dude, thanks a ton!  Unfortunately the board part number doesn't match up for some reason (schematic is for 35-00-0137, mine is 35-00-0047), and many of the part numbers and pins don't match what I'm seeing.  For example, the resistor in question connects through to pin 7(?) of the VDI plug, which should be AES+, but connects through pin 3 of the main harness, which should be ground.  The harness itself should be a 32-pin on the schematic, but on my guitar is a 24-pin.  Anyway, according to the schematic, the AES+ line connects straight through to x with no resistor in line, but my board doesn't even have a x on it.  R48 leads to a x x diode which leads to an x.

 

Regardless, the service manual is still super valuable, since it tells me what type of signal goes in and out of the main DSP chip and a few other key chips that are the same on my board as the schematic, but sadly there are way too many differences.  Really wish Line 6 made these public.

 

 

On 11/24/2018 at 2:51 PM, codamedia said:

 

Nice resource... thanks!

 

OP: Based on that resource, R46 and R48 should be the same value... keep in mind you can't test components in a circuit without getting unpredictable results. That resistor looks gone to me... even if it still had any life, I'd be replacing it. 

 

I agree that I can't expect accurate results measuring in-circuit, but since the schematic doesn't match what I have and the resistor connects straight out to a single pin at the VDI plug there shouldn't be anything in a circuit with it, same as R43 right below it which is a x ohm resistor (marking is x) and measures accurate to 100 ohms, so I'm fairly confident in it's measurement (and in it's crispiness).  I think R48 should match R43, since they both connect to the same type of dual diode, but that's REALLY hard to say.

 

think that particular pin goes to x on the x which I assume is a chip select of sorts, but I can't find it in the datasheet.  Brain hurts...

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No problem, psarkissian. I totally understand, and won't share the link again.

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Thanks.

I don't want any of you to get in trouble.

Just watching your backs. Rock on!!!

 

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Don't worry, we wouldn't have gotten in any trouble. In the United States, only the person who puts the infringing material online is liable for copyright infringement. Individuals who encounter it or provide a link to it are exempt from copyright infringement claims.

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So long as you don't mass distribute.

But yes, they are on the hook for making it available via the link. Very good, you know

your US Title 17 copyright law. Not bad.

 

SSL isn't too worried about their 4000-G mixer service manual being out there much.

Technology from the 1980's and still sounds great. Only guys like me would want to service one.

Newer product, they are protective of it. Maybe in ten or twelve years, we may be like that,...

who knows what the future holds.

 

I guess any queries on the subject can be referred to the rules of Forum use before hand here.

It's good practice. Keep up the good work.   :)

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On ‎11‎/‎24‎/‎2018 at 2:01 PM, tertiumsquid said:

///

 

 

there is  "x10" (or 01x) on R48

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