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Let's Get Technical => Troubleshooting Problems => Topic started by: Dante on October 17, 2016, 08:28:19 AM

Title: Viper trouble
Post by: Dante on October 17, 2016, 08:28:19 AM
Viper troubleshooting topic split and moved.

Hey Stanski,

My Classic did the same thing you described. I was using the Brown channel, with a heavy overdrive (not quite distortion) tone, and it got louder as it warmed up. Thing is, later on, it went back down and came back up again. Just a couple dBs of difference, but the drive also fluctuated (cleaning up when the tone went down).

It has done this before, but I thought I remedied it by replacing the toobs with the original (very old) toobs. I wonder if it's a tube thing or if the Viper and Classic share some sort of circuitry that causes this  :dunno:

Maybe try a different set of tubes?
Title: Re: Viper trouble
Post by: Harley Hexxe on October 17, 2016, 03:26:44 PM
Hey Dante,

     I'm pretty sure Kim would have already tried the tube rolling in that Viper, as that would have been the easiest fix. I also believe the Classic tone would live in that amp to a degree since that was the current MP-1 preamp that was on the market at the time the Viper came out, and the original had already been discontinued for 3 years.

      Harley 8)
Title: Re: Viper trouble
Post by: Kim on October 17, 2016, 03:46:50 PM
I'm pretty sure Kim would have already tried the tube rolling in that Viper, as that would have been the easiest fix.

Yep, that was the very first thing I did when it went out.  At that time a had about a dozen known good tubes to try, with no change to the Viper's operation. I didn't see anything else obviously wrong in there either.   :dunno:

Dante might even recall, that him and I were actually talking on the phone while I was playing the Viper when suddenly right in the middle of a riff the sound dropped to near-nothing. 
Aside from trying different tubes, I simply have not found the time (or patience) to sit and try to figure out what's wrong.  I contacted Matt T. a few times to see if he could go through it, but he always seemed to be swamped with other things.
Title: Re: Viper trouble
Post by: Harley Hexxe on October 18, 2016, 04:50:48 AM
You know, from that description when you were on the phone with Dante, I would say that is a capacitor that is not completely dead, but getting there. It could be a poor connection at that cap, but I've seen a few weak ones act just like that in other amps.
Title: Re: Viper trouble
Post by: MarshallJMP on October 18, 2016, 10:10:46 AM
Could be a cap but it could also be the buffer fet after the tubesection. Or some in the either switching logic or the audio switch circuit.
Title: Re: Viper trouble
Post by: Harley Hexxe on October 18, 2016, 02:32:24 PM
Could be a cap but it could also be the buffer fet after the tubesection. Or some in the either switching logic or the audio switch circuit.

    If it was in the switching logic, or the audio switch circuit, wouldn't that show up as a difficulty in switching the channels then? Because Kim was already in the channel and playing through it for a certain amount of time before it suddenly just dropped out, that is what makes me think of a cap. It could be the buffer FET, or maybe a combination of components in the channel circuit. If this amp is a prototype, then it would make sense they had a problem like this before it's release and had to modify the circuit. So, the next amp would have gotten the updated PC board, and maybe this one got left behind? :dunno:
Title: Re: Viper trouble
Post by: MarshallJMP on October 18, 2016, 02:37:42 PM
Well they use fets to switch the channels in and out so if a fet it busted it won't let the signal through.Same with the switch logic,if something is wrong there the fet won't be switched on.And if the buffer is busted no signal will come through either.
Hard to tell without some measuring.
Title: Re: Viper trouble
Post by: Harley Hexxe on October 18, 2016, 02:49:33 PM
Well they use fets to switch the channels in and out so if a fet it busted it won't let the signal through.Same with the switch logic,if something is wrong there the fet won't be switched on.And if the buffer is busted no signal will come through either.
Hard to tell without some measuring.

    Yes, exactly! But the amp does switch channels, and sound does come through, but drops out on one channel after a certain point, then comes back in. You're right though, without getting into it and measuring the voltages, it's just speculation right now.
Title: Re: Viper trouble
Post by: MarshallJMP on October 18, 2016, 02:51:11 PM
it's just speculation right now.

Yes it is.
Title: Re: Viper trouble
Post by: Kim on October 19, 2016, 02:53:24 AM
...But the amp does switch channels, and sound does come through, but drops out on one channel after a certain point, then comes back in.

The amp does switch channels.  But the Red channel has a very weak volume output right off.  It dropped volume that first time and hasn't returned since.  The gain seems to be there, but the actual volume is very low.

Viper troubleshooting topic split and moved.
Title: Re: Viper trouble
Post by: MarshallJMP on October 19, 2016, 07:46:06 AM
Well my first guess is the buffer behind the red channel.It's also causing problems in the classic so...
Now in the viper there are 2 buffers,almost identical to each other (some different resistor values).One for the clean channel (Q5 + R32,42,44) and the red channel (Q8 and R59,60,61).The viper is different from the preamp because the clean signal is tapped after the first tube and also goes to the red channel.We know that the clean works so you could measure some voltages on both buffers and compare them to each other.They will be a bit different but not much.Maybe you could start there Kim?
Let me know if you need some assistance.
Title: Re: Viper trouble
Post by: Harley Hexxe on October 19, 2016, 12:22:19 PM
Kim doesn't have the amp anymore, Stan does.

What kind of problem is this buffer causing in the Classic?
Title: Re: Viper trouble
Post by: Dante on October 19, 2016, 12:40:58 PM
I'm not sure, but I think he's talking about the issue I mentioned. My Brown channel was losing a bit of gain, then coming back up, like a really slow oscillation. It only lost the gain temporarily, and I suspected a bad toob.

Title: Re: Viper trouble
Post by: MarshallJMP on October 19, 2016, 01:49:06 PM
Yes but Kim has still access to it right Kim?

Problems with the tube channels, like low output and distorted sounds.

In your case Dante I think that was a Tube issue, the buffer problem,once it happend was there to stay, it didn't resolve itself.
Title: Re: Viper trouble
Post by: Harley Hexxe on October 19, 2016, 04:39:15 PM
    Yes, I'm sure Kim still has access to it.

   Fortunately, I haven't experienced anything like that with my Classic.

     Harley 8)
Title: Re: Viper trouble
Post by: Kim on October 20, 2016, 02:48:26 AM
The Viper used to be mine; it's Stan's now.  There's a chance we may take a look into it again this weekend.
Title: Re: Viper trouble
Post by: MarshallJMP on October 20, 2016, 05:01:41 AM
Kim, let me know if I can assist in any way.
Title: Re: Viper trouble
Post by: StanSki on May 04, 2018, 03:04:59 PM
Well my first guess is the buffer behind the red channel.It's also causing problems in the classic so...
Now in the viper there are 2 buffers,almost identical to each other (some different resistor values).One for the clean channel (Q5 + R32,42,44) and the red channel (Q8 and R59,60,61).The viper is different from the preamp because the clean signal is tapped after the first tube and also goes to the red channel.We know that the clean works so you could measure some voltages on both buffers and compare them to each other.They will be a bit different but not much.Maybe you could start there Kim?
Let me know if you need some assistance.

Found Q8, R59, 60, & 61. Now if I only knew what voltages to look for. I'm an advanced newb at this stuff but trying to learn as fast as I can. Always been more of a "yeah, it's burnt, just replace it" kinda guy. See a part physically toasted to know it's bad and needs replacing. This sneaky "looks good but gotta test it 'cause that could be the problem" stuff is not yet common to me regarding values and voltages etc. I'm watching tons of D-Lab, Guitarologist, and other U-Boob electronics gurus to get a clue, but I'm still flailing. I can read the bands on the resistors to get their values so that's a start, which will lead me to their voltages. But Q8 is a transistor so I'm outta my depth on that.
Title: Re: Viper trouble
Post by: MarshallJMP on May 05, 2018, 01:24:28 AM
A transistor can be tested with a multimeter that has a diode check. Look around on the net on how to do this. It's fairly easy. Now this only works for transistors ,not fet's or mosfet's.