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Messages - gearhead63

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Amplifier Discussion / Re: crate gfx 212 need repair help
« on: May 07, 2015, 05:07:44 PM »
What rail voltages were you getting before correcting the bridge rectifier problem and were the + and - voltages on the proper rails??
What voltage are you getting at your speaker output, volume down, no speakers connected? (DC)
You need to keep the speakers disconnected until you figure out whats going on!
Also, have you checked the speakers to see if they're still good?
Did you check your +/-40v rails with Q12,Q13,Q15,Q16 removed (at the transistors)?
(those are the OP transistors you replaced.)
I would check IC3 (NE5532) and IC5 (TL072).
If there was a reversal of polarity in the power supply chances are those IC's are toast.
I would definitely start with those IC's, they control the base voltage of those OP transistors. If they are toasted you better check all the other IC's in the amp.
They really hate reverse polarity! I'd almost bet your gonna find other issues because of that bridge rectifier.

« on: October 14, 2014, 12:09:59 AM »
This is an excellent reference book. Explains the operation and theory of all the different type of audio amplifiers (solid state), with schematics etc. as well as typical uses for power transistors. Can help a lot when troubleshooting transistor amps.

Schematics and Layouts / Re: Fender SR8300P Powered Mixer Schematic
« on: July 04, 2014, 06:09:28 PM »
I just downloaded and opened it with no problem!

« on: July 04, 2014, 06:02:12 PM »
I called Soundtech Support and got a copy of the schematic for the MC100 power module. I haven't got to compare it to my amp yet, but he said this is the only one they have for it, and they do not produce that amp any more.

Amplifier Discussion / Re: LINE 6 FLEXTONE III SCHEMATICS
« on: June 21, 2014, 10:53:52 PM »
Appreciate the info! Now if he will just show up with the amp!

Schematics and Layouts / Fender SR8300P Powered Mixer Schematic
« on: June 21, 2014, 10:29:22 PM »
Took me a while but I found this so I could fix this mixer.

« on: June 05, 2014, 09:22:22 PM »
Does anyone happen to have a copy of the schematics for a Flextone III?

Amplifier Discussion / Line6 Spider III 120
« on: June 01, 2014, 12:21:03 PM »
Does anyone know if the circuitry for the Spider III 120 is comparable to the 75?
And if not where I might obtain a schematic for the 120?
I have a guy that has a 120, and one day it just showed 8 dashed lines on the LCD with no output. I saw on another forum where someone had a Spider III that did the same thing, turned out to be an SMD cap on the preamp board, but as Line6 repaired it, he didn't know which cap it was. I have schematic for the 75 and HD150, but not the 120. He lives a good ways from me, so I don't have the amp in front of me,yet,to compare the PCB to my schematic.
Any help would be appreciated.

Schematics and Layouts / BEHRINGER GMX212/GMX1200H SCHEMATIC
« on: May 28, 2014, 12:52:23 AM »
Here's the schematic for Behringer GMX212 and GMX1200H amps. Finally found one and thought I'd share. Behringer acts like the the world will end if they give you any information!

Actually, if you want to accurately measure the ripple in the power supply you will need an o'scope. Your multimeter will not accurately measure it!
I checked the filter caps in my VTX, in circuit. There are 2 parallel sets of 2 in series across the neg & pos rails, and without unsoldering one end, they showed to be ok with a Huntron Tracker. But one of the caps on the +15v rail was bad! And you have the same kind of setup that your power supply schematic is showing. C42,through C67 are all interconnected between the pos & neg voltage rails and ground.You may not be getting a proper reading unless you unsolder one side of each cap before checking it.In fact after looking at the main schematic, that amp has quite a few "bypass"/filter caps in it that go to ground. Each opamp power pin has a .1uF cap. One of those could possibly be a problem. Did your amp have the hum before you replaced op amps?

Amplifier Discussion / Re: Peavey VT classic 2x12 issues
« on: May 27, 2014, 10:47:25 PM »
First you need to find out if it's the preamp or power amp causing the problem.
Run into another amp from the preamp out and see if it keeps working. If it does then it's a power amp issue. If it cuts out then it's in the preamp section.
Hook a preamp, mixer, what have you, into the power amp in and see if it cuts out. That will tell you where to start looking.

Amplifier Discussion / Re: Two Amps Into One Speaker?
« on: May 14, 2014, 02:21:06 PM »
PLUS..... you may need a dummy load that will load the output of the amp you switch out. I wouldn't do it. Easier to use an ABY on the input signal and have 2 completely separate amps.

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