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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 2:25 pm
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fretworks wrote:

I am trying to learn, so when i ask if I test a resistor without unsoldering one leg, and it tests to schematic spec, is that not reliable, or do I always have to unsolder one leg. .


By reading schematic you may know if reading make sense or not . If not or not sure , you must disconnect one leg .


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 2:35 pm
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Always unsolder one leg of a resistor before doing any static resistance readings. Many resistors are in a time-constant related circuit. So, they are interacting with other components.


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 4:26 pm
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Disconnected r20 and retested good 330k

Resoldered back into circuit and checked pads around and trace all looks and test good

I testedc r22 cr23 and q1 while still in circuit and i will unsolder , test, and post both results.

Removed j3 power amp in jack and am currently testing it.

Will then move on to bypassing part of jack for
Testing of jack.
This might prove difficult as
There are not hard wires connecting jack pins, but instead soldered traces. Not sure how to keep jack in place and from touching pin to pad of the ones we want to disconnect.

Does anyone know if the clear plastic cover on these jacks can be removed without damaging it?


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 4:47 pm
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" There are not hard wires connecting jack pins, but instead soldered traces. Not sure how to keep jack in place and from touching pin to pad of the ones we want to disconnect. "

I don't think that this can be done. Avoid applying too much force on these soldered connections, as this can lead to permanent damage to the tracings. I'd rule-out everything else before looking at the jack.

Then maybe, just do a static continuity test with and without an inserted patch cord. Tip of patch cord and the soldered portion of board. And the corresponding grounding points. Check for poor solder points. Esp any jack or pot soldered to the board.

Good luck! Keep us informed!


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 5:18 pm
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fretworks wrote:
I have confirmed continuity to ground after r20, so am I right to be certain that something is shorting or opened to ground?.....

Q1 how do I test, and can this be removed to see if is the problem?


Q1 functions as a muting circuit when switching between normal and drive channel. When switched, the signal path is momentarily shorted to ground. If you are measuring a short from the output of R20 to ground, Q1 is either shorted or there is a problem in its power supply that is keeping it active. If you simply run a jumper from the output lead of R20 to the input lead of C14 as stratele52 suggested, you can jumper around the power amp in jack and verify continuity to the phase inverter input without removing any parts.

U1A and U1B are input and output buffers for the effects loo and are not part of the signal path unless a plug is inserted into the preamp out and/or the power amp in jacks. I would not waste any time with them.

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 8:47 pm
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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 10:26 pm
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strings10927 wrote:
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If that's all you have to contribute, why did you even bother posting? We are trying to help someone with an amp problem and all you do is take up space. :roll:

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 12:35 am
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It's 2:30 a.m., and I am too tired to post details.
I will say that I have volume now, and plenty of it, but problems aren't completely solved.
Details to follow when I awake.
Thanks for your continued help with this


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 12:47 am
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fretworks,

Well, it sounds like you are heading in the right direction. BTW... you do custom frets?


Thanks!


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 1:08 am
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fretworks wrote:
It's 2:30 a.m., and I am too tired to post details.
I will say that I have volume now, and plenty of it, but problems aren't completely solved.
Details to follow when I awake.
Thanks for your continued help with this


Excellent. :D

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 3:03 am
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fretworks wrote:
It's 2:30 a.m., and I am too tired to post details.
I will say that I have volume now, and plenty of it, but problems aren't completely solved.
Details to follow when I awake.
Thanks for your continued help with this



Great :D

By the way , you post in the Vintage Amp Forum ( anything before 1985 ) :lol:


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 10:21 am
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bluesky636 wrote:
If that's all you have to contribute, why did you even bother posting? We are trying to help someone with an amp problem and all you do is take up space.


Sorry, that's entirely my fault for assuming some people in this part of the forum might actually have a sense of humor. I apologize for the .2 seconds you wasted scrolling. :roll:

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 11:12 am
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strings10927 wrote:
bluesky636 wrote:
If that's all you have to contribute, why did you even bother posting? We are trying to help someone with an amp problem and all you do is take up space.


Sorry, that's entirely my fault for assuming some people in this part of the forum might actually have a sense of humor. I apologize for the .2 seconds you wasted scrolling. :roll:


My suggestion? Stick to the Lounge. Its a better fit for your talent.

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 11:41 am
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thanks for your suggestion, I'll file it with the others.

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Mon Dec 23, 2013 12:34 pm
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OK, after several distractions early today, I am back at it.
Where to start?

Yesterday I checked all suggested components by de-soldering one leg.
All test to spec.
In regards to cr22 and cr23 I don't know what the values should be, but they both were right around 2Mohm.

I could not jumper from r20 to c14 because c14 is mounted close with no room to get a clip or probe on the leg. I pulled the top board down and tried from the back side, but still not enough to clip to.

Instead I unsoldered power amp in jack and tested it per the schematic. Jack is fine.

Removed q1 with no change. Then I dropped the board down again and thought I would probe for audio at c 14 back side, but before I started probing , I finally had sound - and very loud at that.
So now I am thinking I missed something with board up, and maybe q1 was the problem after all.

I then moved the board around a bit with a wooden dowel and all was still well. Screwed the board back in and no sound, just nasty hum.
Pulled board back down, and i have sound again.
Board up again and no sound.
Now I am thinking something on the back of board is touching metal stand offs, or something with the pots.
Tested for those and that was not the problem either.

Pulled board down a 4th time and this time no sound in down position out of chassis, where I had sound before. I moved the board a bit and got really loud popping to the point I am worried about blowing a good speaker. I don't own a dummy load.

Whatshould I concentrate on next? Ribbon cable ?
What is anyone's take on replacing those ribbon cables with individual wire?
Am I guessing in the right direction? Seems to me that if it were components, they would not cause the popping when i barely move the board. Seems like stress on the fragile cables or connections at the board. I will look for lifted traces there.
Any other ideas?

After I find this, I will need to see if q1 had anything to do with bring back sound, or was it just a coincedence.

Lastly, I apologize for posting in the wrong section.
Thanks again for sticking with me.
Today is the day I will conquer this amp!


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