Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Reduction => Topic started by: cpditter on September 19, 2020, 07:52:21 AM
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Hi:
Just finished the Shunt Regulator board and one of my LED's is not working...Not sure what to check to see what is wrong.
Pic attached.
thanks
Chuck
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There's a voltage check on page 23. Can you let us know what you get for that voltage check?
I see lots of long leads poking out of the top side of that board, which makes me want to see what's going on underneath the board as well...
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Sorry that was sloppy, I just did not snip the leads on the connection wires from the preamp...did now. Pic of underside attached.
voltage readings in order of the manual:
134
144
147
Note, my wall voltage is high...I believe in the 130+ range...
Thanks
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You may have solder bridging two terminals on the bottom side of that board, and that would cause some of your issues.
You gave me three voltages and didn't assign them to terminal numbers; the manual lists for terminal numbers to check... Did you have 6922 tubes in the sockets when you performed this set of voltage checks?
How about the voltage checks on page 17?
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Hi
Those were the voltage readings on p. 17, so the two MJE5731 readings were 134 and 144, and the terminal 56 reading was 147v
I'll pull the board back off the preamp and take a better pic of the bottom side and will also look for any solider bridging...
Thanks
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I would absolutely reflow every solder joint on that board other than the LEDs as well.
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OK
I think I found a solder bridge between two pins of the MJE5731 on side B...fixed that with some solder wick. Reflowed most all the joints.
Reconnected and now all 4 led's light.
Voltage readings from p 17 are now as follows
MJE5731 are 123 and 124v
Terminal 56 now 127v
Good to go?
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No, the tabs on the MJE5731As should read lower than terminal 56. Can you post some photos of the power supply and where you have the extra 1K resistors installed? Also you didn't mention whether you had the 6922s installed, but I would recommend installing them if you do not have them in already, then repeat these tests.
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Hi
Yes, tubes are in.
Photos requested attached, let me know if you need more.
Voltage at tabs on MJE5731 are lower than term 56...but not enough lower?
Again, readings on the transistor tabs are 123v and 124v and readings at term 56 is 127v
Thanks
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All of the joints in that photo should be reflowed, possibly with a little more solder added. Heat them up till the solder liquifies, then wait for it to flow where it wants to flow. It doesn't look like the flux has flowed out of most of those joints.
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OK, will do that tomorrow...thanks for the quick responses as always!
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Hi:
Well, I reflowed and added solder to pretty much all the connections on the unit as well as the new board,
Readings as follows
A-side MJE731: 123v
B-side: 124v
Terminal 56: 127v
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What voltage do you get at terminal 50?
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Hi
Terminal 50 is 146v
p.s. Not sure if you saw in earlier post, or if it matters, but I know my wall voltage at our house is high...I believe close to 126-127v
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How about 53?
The wall voltage isn't particularly concerning.
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Terminal 53 is 166v
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How about the voltage at X on each side of the PC board?
Your C4S current sources are working properly, as we see about 40mA of current being pulled across the power supply resistors. The only real issue that I think you're having is that the four zener diodes on the PC board don't appear to be pulling down the regulated rail. Measuring the voltage between them will provide another helpful data point.
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x on the B side is 53.6v
x on the A side is only reading a few 3-4mv
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So x on the B side being 53.6V would suggest that Ob should be around 107V, which is what we are aiming for.
X on the A side being 3-4mV means either those zener diodes on that side aren't well soldered or maybe (but less likely) the ground jumper isn't well connected.
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OK, I'll resolder that Zener diode and resolder the ground wire and then check again...will do in the a.m. when I am fresh!
Thanks again for sticking with me on this...
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It's also worth double checking that all the zener diodes have the correct part number written on them.
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Good morning
I desoldered the ground jumper and the zener diode joints. That resulted in both readings at x now being 53-54v
My other reading:
still at 122 and 123v on the transistor pins and
Term 56 126v
Sorry I could not verify the values on the zener diodes without unsoldering them all...
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Correction on last post line 1, meant to say resoldered, not desoldered.
thx
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still at 122 and 123v on the transistor pins and
Term 56 126v
Both x pads being 53-54 is a good sign. That's half the zener stack on each channel. The voltage at the metal tab should be about 2x that.
What voltages do you get at OA and OB? Can you reflow the center leg of each MJE5731A and reheat both ends of each zener diode connected to OA and OB?
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Hi
OA and OB both reading 107v
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OA and OB are connected to the metal tab of the MJE5731A, so I'm not sure why you have a different voltage there. It may be that getting good probe contact on the metal tab is a bit of a problem in your case for some reason.
Either way you're OK to continue with the build.
-PB
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Thanks!
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Hi:
The rest of the build went fine...up and running, will give it a good listen tonight.
Thanks again for the assistance...guess my soldering skills (which are probably not great to start with) were really rusty when I started this process :)
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I'm glad to hear you got it up and running!
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Hi:
I've now listened to my Reduction with the newly-added Integration upgrade for about two days...
What I'm hearing so far is this:
Overall noise floor is reduced...not that it was bad before but definitely very quiet now.
Gain is noticeably higher so I'm listening with the volume at a lower setting than previously...used to be a very dramatic difference between phono and a line source like my CD player...now that difference is much less.
Can't say I'm hearing a big difference in bass response per se...but, some of the lower end like kick drum seems tighter and just pops out of the mix better I feel.
Thanks again for the help on the build