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Pearl 2 phono
Pearl 2 phono
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Old 3rd March 2019, 10:31 PM   #1
no_op is offline no_op  United States
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Default Pearl 2 phono

The pearl 2 phone pre that I just finished is not working and I can not figure out why. The rectified voltages look fine but after that everything goes pear shaped.

I replaced the zvp3310 (which is why they are airborne) in case I had statically damaged those components but that did not make any difference.

I checked all the resistor/cap values and semi placement but everything appears correct.

I attached a picture of one channel (both channels are not working in exactly same way) and a picture of the voltages I am reading (in pencil) compared to the expected values (in red)
If anyone can point me to a likely fault in the build that would be hugely appreciated.

Click the image to open in full size.

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Last edited by no_op; 3rd March 2019 at 10:48 PM.
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Old 3rd March 2019, 10:44 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by no_op View Post
The pearl 2 phone pre that I just finished is not working
Please fix the photos.

Unless wrong parts are installed the same way in both channels,
the power supply is most likely the place to start.
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Old 3rd March 2019, 10:51 PM   #3
no_op is offline no_op  United States
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Photos fixed.
I ruled out the power supply since the rectified voltages +23 / - 24 look good - both channels.
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Old 3rd March 2019, 11:38 PM   #4
PRR is offline PRR  United States
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Bad solder joints.

Your voltages don't make sense unless it is not really connected according to plan. Some of those solder joints look dubious to me. When there is more than one unrelated wrong reading, you probably have more not-really-connected solder joints than you know.

Get an old VCR and practice on the PCB, taking parts out, putting them back in, and ohm-metering the joints to prove they connect. Technique is everything. A not-crappy iron helps. Flux is essential.
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Old 3rd March 2019, 11:52 PM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by no_op View Post
I ruled out the power supply
What do you mean by ''everything goes pear shaped'', and can you post a scope photo of that waveform.
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Old 4th March 2019, 12:14 AM   #6
no_op is offline no_op  United States
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PRR > that did sound like a promising lead but when i impedance tested all the connections everything looked good. I could not find any opens.

rayma> "by everything goes pear shaped" - i measure -23.85 at the zero adjust pad on both channels.
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Old 4th March 2019, 07:41 AM   #7
Stanislav is offline Stanislav  Australia
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Something's not right around R8 / R10.
Either bad solder joints, as PRR said, or the resistors are bad.
But your soldering technique looks suspicious there.

Suck the old solder with a solder sucker and then apply fresh new one with a suitable tip, heating equally the solder pads and the legs of the resistors.
Use 60/40 solder.

Try to get 9V at the base of that ztx450 first.
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Old 4th March 2019, 05:06 PM   #8
no_op is offline no_op  United States
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Thanks everyone. I will check out R8 /R10 when I get home from work...
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Old 6th March 2019, 01:45 AM   #9
no_op is offline no_op  United States
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All,
Today I was checking the R8/R10 area of the board. I noticed that the passlabs supplied jfets are part j74 bl9c The BOM calls out 2sk370. Isnt that my problem?
Thanks
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Old 6th March 2019, 01:49 AM   #10
rayma is offline rayma  United States
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Quote:
Originally Posted by no_op View Post
I noticed that the passlabs supplied jfets are part j74 bl9c
The BOM calls out 2sk370. Isnt that my problem?
Sounds like it, those are opposite polarity devices.
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