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Circuit error in Lite DAC-AH: Easy fix - Page 7

post #91 of 192
10/30/06 at 5:34pm
So...

I did this mod and seem to have screwed something up somehow. The audio volume is much lower now and there is a ton of static.

Im not sure what obviously, but I seem to have damaged c6,right below R35 (towards the power switch)

It looks like I melted the corner of it somewhat. Can anyone tell me what part this is so I can replace it, or what else I could have done?

Also stock what should the voltage be at on pins 5 and 7 of the TDA1543s? I get about 3.88
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post #92 of 192
10/30/06 at 6:38pm
I believe C6 is 106 uF
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post #93 of 192
10/30/06 at 6:49pm
Thread Starter 
Quote:
Originally Posted by _Rand_
So...

I did this mod and seem to have screwed something up somehow. The audio volume is much lower now and there is a ton of static.

Im not sure what obviously, but I seem to have damaged c6,right below R35 (towards the power switch)

It looks like I melted the corner of it somewhat. Can anyone tell me what part this is so I can replace it, or what else I could have done?

Also stock what should the voltage be at on pins 5 and 7 of the TDA1543s? I get about 3.88
I also melted the corner of the same capacitor, but that didn't seem to cause a problem for me. Of course your damage could be worse.

The volume should be a little lower, but not much. I suggest listening to one channel at a time to see if the problem is isolated to one channel. Also, double check your resistor values. If the values are correct (about 150 ohms) and the problem is in both channels, then you are probably right -- the capacitor is damaged and needs to be replaced.
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post #94 of 192
10/30/06 at 6:50pm
Thread Starter 
I forgot to add that 3.88V is too high. Should be about 3.3V, but may not be your problem. I'd try adjusting the trimpot.
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post #95 of 192
10/30/06 at 7:20pm
Adjusting the trim pot doesn't seem to do anything actually no matter how much I turn it, Just how much do you have to turn the damn thing?

Plus I removed the resistors while trying to figure out what the the hell I did. The problem is the same whether the stock resistors or with the resistors in parallel. mine actually worked out to about 170r instead of the 163 you say is ideal, which isn't too far off I suppose. Better than 270 I would think .

And the problem is in both channels. Im fairly certain I damaged C6 beyond repair I can actually see something dark below the blue plasticy casing.

Measuring between pins 5 and 7 on the TDA1543 I get between 3.87 and 3.89v. I guess it depends on how much I play with the trim pot.

I seem to have damaged C8 as well looking at it from another angle. It doesn't appear to be as bad as C6, but if I'm going to replace C6, C8 may as well go with it, and the resistors to a closer value while I'm at it.

What can I replace these two parts with? Something from http://www.partsconnexion.com/ preferably, I just found out they are local to me, like 20 minutes drive.
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post #96 of 192
10/30/06 at 7:55pm
Thread Starter 
Sometimes you have to turn the trimpot quite far to see any change in voltage and then slowly turn it until you get the voltage you want. It's almost like there is some kind of hysteresis. I bought Vishay resistors from partsconnexion and I think they sound great. They cost $6 each, though, and are much larger than the stock resistors. Another option would be Riken 1/2 watt 150 ohm resistors which partsconnexion stocks. I can't help you with the capacitor replacement.

I'm sorry that this "fix" didn't go well for you.
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post #97 of 192
10/30/06 at 7:56pm
Assuming that you damaged the blue caps, I believe they should be 0.1uf. These are film caps with pin spacing 5mm. I replaced all mine with 0.11 uf polypropylene caps. I am not sure about pin numbers for the chips, but when I measure voltage across the dac chips adjacent to the caps, I always see 6V. To see the combined dac chip output voltage, I measure from ground to the input of my bypass caps. This changes with the trimpot adjustment. I would assume that you could also measure from ground to the output of r35/r36.

Good luck
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post #98 of 192
10/30/06 at 7:58pm
Quote:
Originally Posted by _Rand_
Im fairly certain I damaged C6 beyond repair I can actually see something dark below the blue plasticy casing.

What can I replace these two parts with? Something from http://www.partsconnexion.com/ preferably, I just found out they are local to me, like 20 minutes drive.
If you can see down to the polyester in the cap then its pretty my dead.

After a quick glance at the capacitors partsconnexion offers, i dont think they have anything that would work. Youll have to try digikey or welborne labs. WM15 from http://welbornelabs.com/wima.htm or BC2054-ND from http://digikey.com/ should work.
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post #99 of 192
10/30/06 at 8:37pm
Quick question..... before i unsolder the 2 brown 18v wires and 1 grey ground wire from the board, i just wanted to know if its neccessary for the ground wire to stay connected to the board? I know i dont need the 2 brown wires because there is nothing to power but is the grey ground wire needed on the board ?
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post #100 of 192
10/30/06 at 8:48pm
Thread Starter 
Quote:
Originally Posted by pelayostyle
Quick question..... before i unsolder the 2 brown 18v wires and 1 grey ground wire from the board, i just wanted to know if its neccessary for the ground wire to stay connected to the board? I know i dont need the 2 brown wires because there is nothing to power but is the grey ground wire needed on the board ?
The ground wire needs to stay connected. I'd recommend just leaving them all connected since you've removed the components.
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post #101 of 192
10/30/06 at 8:57pm
Like this ?
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post #102 of 192
10/30/06 at 9:06pm
Thread Starter 
Looks great! Let's see it after you install the caps.
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post #103 of 192
10/31/06 at 12:41am
Stupid question, are there any capacitor values that would "work" that I might be able to pull off an old soundcard or something?

Nothing permanent, just something that would work well enough to make sure I haven't done any real serious damage. Or work until I get a proper replacement even.

I don't think its likely I did any major damage of course, especially given the state of the capacitor I screwed up, but I suppose damaging one of the TDA1543s isn't totally out of the question, but I don't think I could do that just by having a soldering iron in proximity for a few seconds...

I have a ton of mostly useless old computer hardware, much of it from the P2 and P3 era. They are of course, covered in caps of varying values.

The only high voltage caps I spotted though were some 4.7uf 50v ones.
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post #104 of 192
10/31/06 at 3:15am
where did you guys get your opa627's? Any place have them for cheap?
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post #105 of 192
10/31/06 at 4:17am
Quote:
Originally Posted by eladioc
where did you guys get your opa627's? Any place have them for cheap?
Ill sell you my old ones that i removed from my dac. PM me



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