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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 12:36 pm
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Also with board down and no sound last time, I did the chopstick test on components and jacks and all was quiet. I only got the really loud popping when i moved the board.


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 1:36 pm
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fretworks wrote:
Am I guessing in the right direction?


I'll be blunt. This is the problem. You are "guessing" at what you should do next instead of following a logical troubleshooting process.

You provided voltages for the tubes. The schematic shows ALL voltages, both AC and DC that are present in the amp. Have you verified every voltage is correct? How are you checking signal continuity through the amp? Do you have an audio signal generator? Do you have an oscilloscope? Are you just checking resistance paths? If you do not have the proper equipment to troubleshoot an amp you will always be guessing and the chance of guessing right is very slim. Based on what you have done and told us the results were, we would only be guessing. CR22 and CR23 are zener diodes. You don't measure their resistance. Again, you appear to be lacking the proper tools. Exactly what tools DO you have? Also, you have removed and reinstalled so many parts ("shotgunning") that there is a possibility that you have damaged the parts or the traces or may just have bad solder joints.

I'm sorry to say this, but I really think that you are in over your head at this point and should take the amp to a professional for an evaluation and possible repair.

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 1:52 pm
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You are close to find it , look look and look .

IMO it is a mechanical problem ; Printed circuit broken , Solder broken , resistor broken , anything wich can do an intermittent contact ?


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Tue Dec 24, 2013 6:45 am
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Tried to post this last night, but website was experiencing technical difficulties, so here it is now.

It's Alive :D
She is alive and strong.
Q1 was the problem
A big thanks to all of you for your wisdom, this was a great learning experience.

Boy, but talk about trying to diagnose with compound problems.

First. I Was right about the fragile ribbon cable. I started the day by doing a really good visual check with a magnifyer and light. Sure enough, first ribbon cable to top board from v1was a mess and had lifted traces and poor connections. I know now that this was my source of confusion yesterday, creating the popping and letting the amp function when board was in down position. Someone had been in this amp before me, and had this cable off. I de-soldered and stripped back ribbon cable about a half inch. Cleaned up the area of old solder and flux with alcohol. Used an exacto knife to scrape along trace to expose copper. Slightly less than a half inch. I did this for all six. Pushed wires through holes and up tight, bent them over against board and lined up with traces. Soldered the wire down along the trace so I now have a good long connection. This worked out well and is a really good firm connection now.

Fired the amp up and she sounds great with no problems. But wait, about 5 minutes into playing , sound dramatically and suddenly drops to very low and distorted. Not like what we started with, but a bit louder than that , but horrible distorted sound. I was really crushed and thought now what? Have I burned a resistor or other component?

I was about to shut it off when i thought to check for anything with the wooden dowel. Surprise. When I pushed on the speaker jack, sound came back full. I bent the jack connections in a bit so that when a plug is inserted the shunt is a bit further away from signal arm. Yet still closes well when plug is out. I also gave it a good cleaning with contact cleaner.

Spent about a half an hour playing guitar through the amp and testing all functions. everything works well.

One odd thing though. When i turn the power off, it turns off fine, but then a second later surges back with a one spike of volume just for a second. Like a quick gun shot. Anyone ever experience this?

Thanks again for all your help Merry Christmas!!! I have a new toy


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Tue Dec 24, 2013 7:13 am
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Wow, an FET went bad? These are sometimes used as current regulators. Did you have a big power surge just before the problem happened? You may want to put a nice heat sink on that transistor. As often they regulate current by converting excess current into heat.

Anyhow, enjoy the XMAS with some good tones.


http://www.webphix.com/schematic%20heav ... eville.pdf


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Tue Dec 24, 2013 8:20 am
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fretworks wrote:
Q1 was the problem


Exactly what was the failure mode for Q1?

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Tue Dec 24, 2013 8:21 am
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BMW2002Ti wrote:
Wow, an FET went bad? These are sometimes used as current regulators. Did you have a big power surge just before the problem happened? You may want to put a nice heat sink on that transistor. As often they regulate current by converting excess current into heat.

Anyhow, enjoy the XMAS with some good tones.


http://www.webphix.com/schematic%20heav ... eville.pdf


As I described earlier, Q1 is part of the muting circuit to prevent pops when switching between the clean and drive channel.

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Tue Dec 24, 2013 8:32 am
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fretworks ,

I'm not surprise about Q1 like a write dec 22 . As many other electronics parts it is on the signal line wich can kill your sound .

As Bluesky write , what is the problem with Q 1 ? You only disconnect them I guess ?

He must be short OR drive short by defective U 4 B or before .

Or Cr2, Cr3 are short


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Tue Dec 24, 2013 5:59 pm
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fretworks wrote:
...When i turn the power off, it turns off fine, but then a second later surges back with a one spike of volume just for a second...


Turn off the standby switch first, wait about 30 seconds, then turn the power off.

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Tue Dec 24, 2013 6:32 pm
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Mike,

Another way to discharge the caps --- turn amp off, as usual. With amp off, turn the STANDBY on for a few seconds. This discharges the last 20mfd caps in the power rail.

Have a Merry XMAS! :D :mrgreen: :D


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Wed Dec 25, 2013 8:52 am
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Merry Christmas

I was not able to reply yesterday.

Q1 appears to be internally shorted to all three legs.

I tested cr2 and cr3 in reverse bias with a couple of 9 volt batteries and a 1k resistor.
Scematic shows cr1 and cr2 at 15v.
They tested 14.7 and 14.9
They seem fine.

I don't use the drive channel or a footswitch.
But, I would like to trace this all the way through to see what might have cause this and if there is anything else odd in the circuit.
Can i jumper around from front side of q1 to the remainder of the footswitch circuit and continue audio probing and voltage probing without damaging anything prior to this?
It works now, and i would prefer to keep it that way.

Lastly, would it work to use a stereo 1/4 cable plugged into the footswitch jack, and short tip or ring to approximate switching?


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Wed Dec 25, 2013 11:57 am
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fretworks wrote:
Merry Christmas

I was not able to reply yesterday.

Q1 appears to be internally shorted to all three legs. Out of the circuit ?

I tested cr2 and cr3 in reverse bias with a couple of 9 volt batteries and a 1k resistor.
Scematic shows cr1 and cr2 at 15v.
They tested 14.7 and 14.9
They seem fine.

You are very qualified ! Congrat



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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Wed Dec 25, 2013 12:47 pm
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Thank you, I am trying.

Yes out of circuit.


I have a fluke 77 that surprising will not read down to the low AC millivolts of the schematic test points.
Any suggestions for a dmm that will read down to 1 mv AC?

Also, I believe I posted this before, but I have an oscilloscope and audio generator that I don't know how to use. I am reading the manuals today.
I have the probes but looks like I need to make a bnc to 1/4 cable to get sound into the amp.

Have been using a homemade audio probe up till this point.

Thanks again for everyone's encouragement and knowledge


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Wed Dec 25, 2013 1:00 pm
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fretworks wrote:
Thank you, I am trying.

Yes out of circuit.


I have a fluke 77 that surprising will not read down to the low AC millivolts of the schematic test points. Good tester no need better

Any suggestions for a dmm that will read down to 1 mv AC? Use a Osccilloscope

Also, I believe I posted this before, but I have an oscilloscope and audio generator that I don't know how to use. I am reading the manuals today.
Look on you tube , there might be good hints .
I have the probes but looks like I need to make a bnc to 1/4 cable to get sound into the amp.
No ,use the probe , no need bnc to 1/4 cable

Have been using a homemade audio probe up till this point.

Thanks again for everyone's encouragement and knowledge


You work one of the most difficult tube amp IMO and you do great job


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Wed Dec 25, 2013 9:27 pm
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fretworks wrote:
...I have a fluke 77 that surprising will not read down to the low AC millivolts of the schematic test points...

Also, I believe I posted this before, but I have an oscilloscope and audio generator that I don't know how to use....


The test points in the ovals are AC, and will only have a reading with an AC signal into the amp input. With no AC into the input, the oval test points are meaningless. With amp on, ready to play, using the signal generator into the amp input 1, set for 1K Hz and about 4 mVAC, per the schematic, then you can read the AC signals at the oval test points. The rectangle test points are DC and can be read with or without an AC signal into the input. Your meter should read mV just fine, there is no signal as low as 1 mV anyway. See the notes on the schematic for setting the pots on the amp.

You need a jack in the amp input to open the shorting part of the jack when injecting an AC signal into the amp.

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Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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