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Old 20th June 2009, 04:44 AM   #761
troystg is online now troystg  United States
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Quote:
Originally posted by madisonears
......
One thing I have noticed while testing my boards, without power, is that some measured resistance values move upward in "steps" to the correct value on the amp that works, but read the correct value immediately on the amp that doesn't work. Does that signify anything to those who know their stuff?
.......
Peace,
Tom E

If you are measuring resistance with the component "in circuit" the resistance will change / step as the connected capacitors in the circuit charge.

If you do not have that variability it either means the cap is charged fully to the potential of the meter battery or the cap is basically "out of the circuit" which would be a problem.
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Old 20th June 2009, 08:39 AM   #762
AndrewT is offline AndrewT  Scotland
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Hi Bhm,
remove the amplifiers from the PSUs.
check the voltages again.
This time measure both the DC voltage and the AC voltage.
and tell us all the readings.
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Old 20th June 2009, 10:40 AM   #763
Stuey is offline Stuey  Australia
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Tom just to explain a little more from Troy's post, your multimeter takes 'samples' on a short periodic basis, hence the stepping display as the caps charge (as Troy points out).

Stu
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Old 20th June 2009, 03:58 PM   #764
bhm is offline bhm  United States
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Default one channel not working

Quote:
Originally posted by AndrewT
Hi Bhm,
remove the amplifiers from the PSUs.
check the voltages again.
This time measure both the DC voltage and the AC voltage.
and tell us all the readings.
Hi AndrewT, Thanks for your help.

Here is a sketch and the voltage readings with the amplifier boards disconnected from the transformers

Blair
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File Type: pdf my_ref power hookup sketch.pdf (10.7 KB, 115 views)
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Old 20th June 2009, 06:19 PM   #765
AndrewT is offline AndrewT  Scotland
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connect the rectifiers and smoothing, but not the amplifiers.
and measure again.
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Old 20th June 2009, 11:21 PM   #766
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Troy and Stu,

Thanks for your response, guys. Yeah, that's what I thought was happening--the caps are charging (or not) in circuit with the resistors I'm measuring. So this might be a clue as to what is wrong with one amp. Does the "non-stepping" indicate that power is going directly to ground somewhere, rather than into the caps? I've checked all the caps and they seem okay, so I don't suspect any shorts there. I simply cannot see or figure out where the short circuit might be. What would be a good way to determine if I've shorted signal or power to ground somewhere and locate it?

I will discharge all caps and try measuring resistances again.

To all: does anyone have a spare board they'd like to sell? If I cannot figure out what's wrong, I'm willing to build yet another amp, but I'd sure like to start with a fresh board. Obviously, I've screwed this one up.

Peace,
Tom E
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Old 21st June 2009, 02:37 AM   #767
bhm is offline bhm  United States
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Default I got my Channel to work

I wanted to report that I got my bad channel to work. Whilst I was trying to figure out how to follow AndrewT's suggestion of separating the power supply after the smoothing capacitors from the rest of the amp, I noticed that I had installed one of the zener diodes (ZD1) with the wrong orientation. Once I turned it around the correct way both channels began to work.

Thanks very much for your help and sorry to bother everyone with such a knucklehead type of problem.

Regards,
Blair
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Old 21st June 2009, 02:54 AM   #768
troystg is online now troystg  United States
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Default Re: I got my Channel to work

Quote:
Originally posted by bhm
I wanted to report that I got my bad channel to work. Whilst I was trying to figure out how to follow AndrewT's suggestion of separating the power supply after the smoothing capacitors from the rest of the amp, I noticed that I had installed one of the zener diodes (ZD1) with the wrong orientation. Once I turned it around the correct way both channels began to work.

Thanks very much for your help and sorry to bother everyone with such a knucklehead type of problem.

Regards,
Blair

NOT a knucklehead problem, just a simple mistake. They happen and it is a PITA to find them. I am happy you found it, and you did it on your own!

Cheers!
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Old 21st June 2009, 03:07 AM   #769
troystg is online now troystg  United States
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Quote:
Originally posted by madisonears
Troy and Stu,

Thanks for your response, guys. Yeah, that's what I thought was happening--the caps are charging (or not) in circuit with the resistors I'm measuring. So this might be a clue as to what is wrong with one amp. Does the "non-stepping" indicate that power is going directly to ground somewhere, rather than into the caps? I've checked all the caps and they seem okay, so I don't suspect any shorts there. I simply cannot see or figure out where the short circuit might be. What would be a good way to determine if I've shorted signal or power to ground somewhere and locate it?

I will discharge all caps and try measuring resistances again.

To all: does anyone have a spare board they'd like to sell? If I cannot figure out what's wrong, I'm willing to build yet another amp, but I'd sure like to start with a fresh board. Obviously, I've screwed this one up.

Peace,
Tom E

If you post detailed pics I will look at each component for proper value and orientation.

You may also send them to me to check out against my working set. You pay shipping both ways and the troubleshooting is free. <Because it is NOT guaranteed!! >
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Old 21st June 2009, 07:22 AM   #770
Stuey is offline Stuey  Australia
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We're just happy it was so simple an error! They usually are...

Good one.

Stuey
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