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    Please help me finish my PAS-2 upgrade

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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 1:15 pm

    With the wires from CN4 connected to PC-5 and PC-6, I measure 275V.
    The 47K resistor isn't accessible from the top of the cap board.
    Both of the 10K resistors on the board measure 9.8K across them.
    By "read short" I assume that means that, with the meter set at its lowest reading (200 ohms), there is no meter response (which is the case, except for the end of one of the 10K resistors where the meter reads 03 ohms)
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 1:35 pm

    With the two wires removed, which of the two CN4 terminals reads short to one end of one of the 10K resistors?  To determine this, take a resistance reading from each CN4 terminal in turn to both ends of both 10K resistors in turn.

    With the wires reconnected, and with the variac set to 120 VAC, and with your meter set to DC volts, please measure from CN4-1 to ground and then from CN4-2 to ground and please let me know what you find.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 2:49 pm

    Measurements of CN4-2 to 10K resistors : 0.3 to nearest end of upper resistor, short to the other end and to the ends of the lower resistor.

    Measurements of CN4-1 to 10K resistors: 0.3 to nearest end of lower resistor; short to the other end and to the ends of the upper resistor.

    With wires connected, 120VAC from variac: CN4-1 - 278 DC volts, CN4-2 - 273 DC volts
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 3:18 pm

    That does not make sense.  Based upon the cap board's schematic (that matches the original PAS topology), and with the wires removed from both CN4 terminals, CN4-2 should have a significant resistance reading to either end of both 10K resistors.  And, CN4-1 should have read short to just one end of one of the 10K resistors.

    CN4-2 is too high at 273 volts.

    I'm not sure what to tell you.  I had some other ideas, but with the one filament voltage so high and with the voltages at PC6 (from CN4-2) above spec, I would not want to try them.

    Did the cap board come fully assembled or did you install the parts?
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 3:50 pm

    The cap board came fully assembled. Should I remove it in order to have access to the solders and traces and thus be able to make some measurements?

    OK, I have; it's easy to do.

    I notice that the board has 3 resistors R1, R2, and R3. They're all mounted on the top of the board. All three are 1W and all have the same color code (brown/black/orange) which of course means 10K. All of them measure 10K +/1 5%.

    Although the the chart shows R3 as 47K, the resistor labeled "R3" on the board is a 10K.

    Could this be part of the problem?


    Last edited by billinrio on Sun Dec 02, 2018 4:34 pm; edited 1 time in total
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 4:27 pm

    You could give that a try. But, you'd then need to be able to scrutinize the cap board and compare what you see to the schematic. You would need to be able to discern if what you see matches the schematic.

    What kind of a meter are you using for the measurements you are taking? Do you have another meter that you can use as a crosscheck?
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 4:38 pm

    billinrio wrote:Although the the chart shows R3 as 47K, the resistor labeled "R3" on the board is a 10K.

    Could this be part of the problem?

    Yes, absolutely that is a problem.  This is one of the things I was attempting to get at.  There needs to be a 47K where there is supposed to be a 47K.  But, some of the continuity/resistance measurements you last reported still don't make sense, regardless.

    I'd also want to visually trace-out the entire circuit on the cap board and make sure it matches the schematic.  Provided the cap board traces match the schematic, do you have a source for a 2-watt 47K resistor?  If the traces on the cap board do not match the schematic, then that's a problem.  Based upon some of the continuity/resistance readings you took, I want to suggest looking for solder bridges or other connections between traces that are not supposed to be there.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 5:00 pm

    My meter is a Wavetek DM5XL.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 5:14 pm

    Perhaps you could try posting a large, clear image of both top and bottom of the board once it is removed.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 6:08 pm

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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 6:09 pm

    Here are the photos of the top and bottom of the cap board.

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    erhard-audio

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    Re: Please help me finish my PAS-2 upgrade

    Post by erhard-audio on Sun Dec 02, 2018 6:12 pm

    if there are issues with the pcb, 'pm' me and I will help you out with our power supply kit. And yes, there needs to be a 47K resistor. It should have two 10K's and one 47K.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 6:23 pm

    Try putting in the 47K. There's a good chance it could set things straight.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 6:40 pm

    Just as all of us, I'm sure, I have a large number of different resistors in my parts drawer.  But Murphy's Law prevails: the one I need is the one I don't have.  I did find a couple of 2W 47K resistors, but they're ancient, and have drifted to 59K.  But caps (some, and not the best) and resistors (most) I can source locally here, which I intend to do tomorrow.  From what I can see, that will reduce, but not necessarily eliminate the problems.


    Last edited by billinrio on Mon Dec 03, 2018 8:08 pm; edited 1 time in total
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 6:51 pm

    You could still have other issues, but the 47K might get us past this one.


    Last edited by PeterCapo on Mon Dec 03, 2018 3:25 pm; edited 2 times in total (Reason for editing : eliminate redundancy and make correction)
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 7:20 pm

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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 7:25 pm

    When you've got it all put back together, please repeat the same measurements you took for Post n°16.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Mon Dec 03, 2018 3:42 pm

    i replaced the 10K R1 resistor on the board with a 47K.   I then measured the pinouts. Disappointing.  Here they are:

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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Mon Dec 03, 2018 9:22 pm

    billinrio wrote:i replaced the 10K R1 resistor on the board with a 47K.   I then measured the pinouts. Disappointing.
    It was R3 that needed to be replaced.  Please put the 10K back into the R1 location and the 47K in the R3 location.  Then, please repeat all your readings with the variac measured at 120 VAC.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Tue Dec 04, 2018 5:09 am

    PeterCapo wrote:
    billinrio wrote:i replaced the 10K R1 resistor on the board with a 47K.   I then measured the pinouts. Disappointing.
    It was R3 that needed to be replaced.  Please put the 10K back into the R1 location and the 47K in the R3 location.  Then, please repeat all your readings with the variac measured at 120 VAC.

    My bad! Rolling Eyes
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Tue Dec 04, 2018 8:22 am

    Here are the readings with R3 @47K and R1 @ 10K.

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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Tue Dec 04, 2018 2:25 pm

    Well, there has been some improvement, but a lot of the readings are still off. One thing I can tell you is that I would not run the preamp at 127 VAC mains. It's not a good way to compensate for whatever else is still wrong.

    So, pins 1 and 6 on the phono board are tolerable now. Pins 6 on the line board are now tolerable, but, curiously, pins 1 are still really low - even lower than they were last week. Rather odd. Your filaments are still too high, as well. My hope was that if we could get the readings up for the B+, that we could lower the variac a bit to see if it would be enough to reign-in the filaments. But, without having the B+ higher, this is not a good option.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Tue Dec 04, 2018 2:41 pm

    I will take your advice about keeping the mains voltage down to 120VAC.  It's a temptation to try to get the numbers up by cranking up the variac.
    I was wondering whether some of the tubes might be at fault - even though they measure "good" on my tube tester, which is ancient.  Googling, I came across a guitar forum (I sometimes think that if it weren't for guitar players, tubes might be unavailable for audiophiles) where there is a discussion about low plate voltages, and somebody suggested removing the tubes and then measuring voltage at the tube pinouts.  I started to try this (with the voltage quite a ways down on the variac), but the readings were quite high, so I discarded that idea.  
    Should I think about replacing the capacitors on the board? Could it be that one or more of them is faulty? I assume that I can't measure them with my capacitance tester while they're in the circuit.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Tue Dec 04, 2018 3:33 pm

    That might be a reasonable possibility except that pins 6 on PC5 are just tolerable. Also, if you have never before changed-out a radial or snap-in electrolytic, you're in for a rough ride. They can be a challenge to remove.

    I am thinking that the kind of troubleshooting this requires may be more than is practical in this kind of setting, unless you want to try something like replacing the cap board with a different one.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Tue Dec 04, 2018 3:56 pm

    I've received no responses from the many e-mails that I've sent to the seller of the cap board. He should send me a replacement board, but obviously, that isn't going to happen. I'll have to look around for an alternative.
    What kind of rough ride would I be in for if I try to remove the caps?
    There are two 1N-5400 diodes (D3 & D4) in the circuit. Could they possibly be a source of the problem?

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