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Post subject: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Mon Dec 26, 2016 1:34 pm
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So my buddy bought this Pro Reverb combo off his neighbor. The amp powers up but has no sound, and yes its the modern "circuit board type". Checked the fuse in the bias compartment, checked all the tubes with tubes out of my amp (they are all new).

Also did the infamous test of the effects return and power amp in and still no sound there. Theres a small circuity board that the Power Tubes (6L6) set into and I found 2 bad diodes, i swapped em out, still no sound.

Checked all the tube sockets both the pin sides and the soldered portions to the board but its all looking good.

Checked plugins on the board, checked for burnt components on the board, I'm looking like a dork at this point because i told him - "No worries my friend, I know my stuff" LOL!! :lol:

Can anyone here think of something I've missed besides the speaker. speaker wire, input jack?

Oh and if i tap the tubes i hear noise but thats bout the only way the amp produces any kind of sound.


Thanks!


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Mon Dec 26, 2016 1:49 pm
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Did you check the output fuses with a DVM (DC resistance continuity). Sometimes, tiny fuses look okay, but are really blown.

If all fuses pass continuity test... best to do some voltage checks. I presume this is the amp's schematic?

http://ampwares.com/schematics/Pro_Reverb_Schematic.pdf


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Mon Dec 26, 2016 2:03 pm
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BMW2002Ti wrote:
best to do some voltage checks.


+1

Start with the basics......heater voltage, screen and grid voltage, the B+.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Mon Dec 26, 2016 7:08 pm
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BMW2002Ti wrote:
Did you check the output fuses with a DVM (DC resistance continuity). Sometimes, tiny fuses look okay, but are really blown.

If all fuses pass continuity test... best to do some voltage checks. I presume this is the amp's schematic?

http://ampwares.com/schematics/Pro_Reverb_Schematic.pdf



Fuses pass DVM test.


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Mon Dec 26, 2016 7:09 pm
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Retroverbial wrote:
BMW2002Ti wrote:
best to do some voltage checks.


+1

Start with the basics......heater voltage, screen and grid voltage, the B+.

Arjay


Are these voltages tested on pin 3 on power tubes?


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Mon Dec 26, 2016 9:04 pm
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Hmmm. If you tap the tubes, you get noise. That tells me more than all the DC voltage checks. It sounds like most of the amp is working. Which tubes produce noise? Can you hear hiss when you turn it up?

Lets revisit those bad diodes you found.
If they were the diodes on the inset board, D104 & 105, then I suspect the 1 ohm flameproof resistors R116 & 117 also went down.
Flameproof resistors can blow a small band out where you can't see it, so it looks OK.
But if they're blown, there might be no signal path to ground for the power tubes.
Measure the bias at the test point. If the resistors are blown, it will measure .6 volts. If they are OK, the bias will be lower, about .06 volts.


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Mon Dec 26, 2016 10:04 pm
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TimsAudio wrote:
Hmmm. If you tap the tubes, you get noise. That tells me more than all the DC voltage checks. It sounds like most of the amp is working. Which tubes produce noise? Can you hear hiss when you turn it up?

Lets revisit those bad diodes you found.
If they were the diodes on the inset board, D104 & 105, then I suspect the 1 ohm flameproof resistors R116 & 117 also went down.
Flameproof resistors can blow a small band out where you can't see it, so it looks OK.
But if they're blown, there might be no signal path to ground for the power tubes.
Measure the bias at the test point. If the resistors are blown, it will measure .6 volts. If they are OK, the bias will be lower, about .06 volts.


There is no hiss, and the Power Tubes are the ones that make noise when I tap them with my knuckle, no hiss and no volume knob response when I turn up or lower the volume.

The diodes i changed were on the Power Tube Board and they were D102 and D103.

I Tested R116 & R117 and they are reading 1.1 both ways HOWEVER, the TWO DIODES that you mention on the "rear board" the one with all the speaker and effects jacks has D104 & D105 and those are not reading the normal 525 one way and Zero the other, they are both beeping in diode setting both direction and only reading a 1 one way and a 0 the other??

Continuity is usually associated with beeps on my meter but never on usual 1n4007 diode readings??

There are 2 diodes on both sides of the power tube sockets, and only one of each were bad. but again the resistors read good


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Tue Dec 27, 2016 6:01 am
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If diodes D102, D103 are open, the amp will work , short ,no.

Diodes D104, D105 are in parallel with R116 and R117.
You read resistor + diode, not only diode, reading will be wrong. You must disconnect resistor or diode to check diodes.

IMO amp need to see a tech.


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Tue Dec 27, 2016 9:38 am
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Well, I still like guessing games. Hey, its not my amp.
Tapping the 6L6s indicates the main stage is working.
The Effect return goes directly into the phase inverter.
There's not much left in between.
The PI circuit is probably dead. You can pull the PI tube when the amp is on. If it doesn't make a big pop, there is probably no plate voltage on the Phase inverter plates..
Odds are, there is a burnt solder joint on the power supply dropping resistors.
Possibly an open inductor coil.
Look for a tan ooze coming out of the power supply electrolytic capacitors.


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Tue Dec 27, 2016 11:15 am
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TimsAudio wrote:
Well, I still like guessing games. Hey, its not my amp.
Tapping the 6L6s indicates the main stage is working.
The Effect return goes directly into the phase inverter.
There's not much left in between.
The PI circuit is probably dead. You can pull the PI tube when the amp is on. If it doesn't make a big pop, there is probably no plate voltage on the Phase inverter plates..
Odds are, there is a burnt solder joint on the power supply dropping resistors.
Possibly an open inductor coil.
Look for a tan ooze coming out of the power supply electrolytic capacitors.



I've never heard the term "Power Supply Dropping Resistors" are those the ceramics?
And what is an "inductor coil"?
I've checked the Power Supply Electrolytic and they test within their specs and there is no oozing.

:?: :shock:


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Tue Dec 27, 2016 11:17 am
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stratele52 wrote:
IMO amp need to see a tech.


+1!

I determined that after his second post in this thread.

:lol:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Tue Dec 27, 2016 11:20 am
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I believe:

"Power Supply Dropping Resistors" = resistors between main filter caps, in the power supply. Used to drop voltage taps on the rail.

"inductor coil" = choke in the main filter rail.


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Tue Dec 27, 2016 11:33 am
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Retroverbial wrote:
stratele52 wrote:
IMO amp need to see a tech.


+1!

I determined that after his second post in this thread.

:lol:



Arjay


I was sure. :lol:


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Tue Dec 27, 2016 8:10 pm
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The power supply dropping resistors are R205 and R206. They are 10K 2 watt resistors near the large Power supply capacitors. They are larger than most of the the other resistors.
The color code will be brown black orange.
A small plastic inspection mirror can look under the boards with a flashlight or...
Tug on the resistor leads gently to see if either end pulls up. If it does, that's the problem. Good joints won't let go.
The inductor leads are black wires going to a small transformer like device. It connects to P216 and P217.


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Post subject: Re: My Buddies 2001 Pro Reverb - NO SOUND!
Posted: Wed Dec 28, 2016 7:35 pm
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TimsAudio - you nailed it!! They looked perfect, I jumpered the new ones in to test with alligator clips and BOOM! Amp is up and running! Rather than remove the board, I piggy backed them.

Thanks for sharing!!


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