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Old 24th May 2013, 12:31 AM   #91
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Ok, replaced the 10 ohm resistors in r21-24 with 20 ohm, and now get 9.6 and 10.2 v out of r9. Is this difference significant? I haven't looked too hard, but so far can't trace it to anything.

Other than that I can't see anything to do beyond put it all back together and try again.

I fried two more 10ohm resistors and 1 more 7924 if there is anyone taking a tally...
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Old 24th May 2013, 12:44 AM   #92
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Nothing to worry about. May be slight differences in the FETs between channels. Fire it up and play some music!
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Old 24th May 2013, 01:33 AM   #93
6L6 is offline 6L6  United States
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Quote:
Originally Posted by jhsjhs99 View Post
I fried two more 10ohm resistors and 1 more 7924 if there is anyone taking a tally...

When? Which PCB? After you measured the proper voltages when you changed the source resistors?
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Old 24th May 2013, 12:19 PM   #94
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Re: the fried resistors, I believe that I still have issues around the connection of the psu to the pcb's. After I got the second pcb to work, I retested the first (which had already tested out fine), there was a crackle noise, and the resistors at the entrance of the negative input fried. I replaced them and the 7924. Then it worked. My guess is that there is still something going on with the connection between the psu and the pcbs.

I did plug everything in and gave it a spin before work. First off, sound--real sound, Janis Joplin sounded like Janis Joplin, major step forward. But, not yet fully functional. Remaining issues:

1) I need to check the power supply connection as mentioned above--it is not stable in the case, there was some crackling when I tried to set it firmly, as I wasn't hearing one channel. It may be just the need to tighten everything up, but I didn't have time to look.

2) The levels are very different--one channel is comparable to the unit I currently have in place, maybe a bit softer, but not too much. The other was very soft, much less amplification. For reference, I am using a 30W Pass integrated amp, which I normally turn up around half way to listen (not too high a volume). To get a comparable volume, I had the left channel up around 55%, and the right near 100%.

3) there was some crackling on the left channel.

I didn't have time to a/b it, or even really give it a good listen, so I can't comment much on the quality, except to say that (level issue aside) it works--I could use it to play records.

So, I will take a hard look at the connections of the power supply (at a minimum, tightening everything, which I realize I forgot to do). I am not sure what to do about the levels. I will start by testing the voltages again with everything hooked up, see what that tells me.

Thanks as always.
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Old 17th June 2013, 01:58 PM   #95
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OK, I will add more later on this, but...

I have a Pearl II.

Following the previous note, I took apart the riaa and realized that the problematic board had a serious problem--I had fried the voltage regulator so many times that the pcb itself had been damaged (I am guessing from the constant soldering/desoldering process). I was on the verge of punting, and getting a new pcb to start over with that channel, but sent a picture to 6L6 before I placed the order. He said he would give it a shot, so I sent the board to him. A week later it returned, with a nifty little bridge across the damaged part of the pcb (I forgot to photograph, but will the next time I take the riaa apart). There was a small amount of drama following this, but once I got the output/input wires connected to the rca's properly, it worked! The only immediate issue was hum, which was loud enough to be troublesome. It turned out that just moving the riaa away from my integrated amp, and putting the cover on, took care of most of that. If you crank the amp enough and put your head close to the speakers you can still hear it, but if I were to get another stand to get the riaa further away that would eliminate most of that.

The level of the Pearl II is lower than that I am replacing with it (an old musical surrounding phonomena), which makes a/b'ing it a bit tricky. I played with it a bit last night, but ended up just listening to records. Eventually I will do it right, but for now I have the Pearl II in the system.

So, quickly, thanks to all for the help throughout this process (and particularly to 6L6 for general guidance and stepping in at the last moment and saving a pcb). To answer a question I asked on a different thread, yes--a person with no particular background in any of this, and no experience with electronics, soldering, pretty much anything useful in this area, can do it. Try!

I will post a more detailed summary at a later date, with an updated BOM, and anything else that I can think of that I wish I had known. One last time--thanks to everyone for helping out with this, I never would have even tried, let alone finished, if you had not.
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Old 17th June 2013, 05:14 PM   #96
omishra is offline omishra  India
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The board where you are replacing 7924 and burning 10ohm resistances, can you check red led. Here I tested one with reversed LED and it was doing same thing. Worked fine after correcting polarity of that Red led.
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Old 17th June 2013, 05:20 PM   #97
6L6 is offline 6L6  United States
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The PCB that was blowing the regulator had a teeny sliver of wire in the solder that was shorting it out. Everything was removed, cleaned and re-soldered. The PSU voltages are fine.
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