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Mystery PCB
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Old 9th December 2011, 01:17 PM   #1
GringoAudio is offline GringoAudio  Canada
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Default Mystery PCB

I bought a bunch of PCBs a few years ago with more enthusiasm than actual time to work on them. As a result I have at least one completely mysterious PCB. It was from a group buy likely and it has no identifying markings. One side has traces, one side is almost all ground plane. It is stereo and has one small transistor per channel it looks like. Perhaps a Buffer?? Can you guys help me identify this PCB and provided some stuffing instructions?

I also have a legit P3A PCB I bought from a buddy and have no assembly/stuffing instructions. So if anyone can help me there too. ...and I have some Aleph-X boards I know I have somewhere that I will never use ... someone can have these for postage only if I can find them.

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Old 9th December 2011, 01:38 PM   #2
madtecchy is offline madtecchy  England
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Hi Gringo.

I dont know what it is but im taking a guess it is not stereo.

Best regards Ian
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Old 9th December 2011, 01:44 PM   #3
siliconray is offline siliconray  China
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I also vote its not a stereo
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Old 9th December 2011, 06:56 PM   #4
GringoAudio is offline GringoAudio  Canada
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It has four signal connections (2-in and 2-out I am guessing) very close together and despite the irregular layout has two very possibly symmetrical circuits starting with a small signal transistor for each channel. There is a spot for two or four big caps in the middle. One was loaded and not soldered in but I cannot remember the value. I can look when I get home.
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Last edited by GringoAudio; 9th December 2011 at 06:58 PM. Reason: added forgotten word.
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Old 10th December 2011, 12:52 AM   #5
Enzo is online now Enzo  United States
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I have no idea, but there are possibilities other than "stereo."

For example a couple LEDs on one end shining on a couple phototransistors on the other makes a dual photo-interruptor. SOmething like that is used in limit sensing in equipment or even steering wheels on arcade games.

On the other hand, extensive ground plane like that might suggest low signal levels, such as antenna booster or some sort of preamp thingie.

How about this: the two red circled three-holes hold three-leg voltage regulators. A dual polarity power supply board. That would explain why the top one has the line from the filter cap feeding the center pin while the lower one had the feed to the end pin.

Just a thought.
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Old 10th December 2011, 05:25 PM   #6
GringoAudio is offline GringoAudio  Canada
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Thanks guys. About 6-8 years and two big concussions between the purchase of this and other PCB boards and I just cannot remember anything about it/them!
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Old 10th December 2011, 09:33 PM   #7
mickeymoose is offline mickeymoose  Canada
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The 2 big holes on the East (plus the one smaller one next) more than likely are for a DC socket
About the concussions: Stop beating yourself on the head with unmarked pc boards! E
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Old 10th December 2011, 10:23 PM   #8
GringoAudio is offline GringoAudio  Canada
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A power supply with two regulators makes sense. I will pursue analyzing it from that angle.

As for the concussions... downhill mountain biking is something I have to give up. At 53 I am finally admitting that it is a younger man's game. Thanks.

It would still be nice if someone recognized this exact PCB though!
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Old 11th December 2011, 06:28 AM   #9
jitter is offline jitter  Netherlands
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It seems to me that the designer used square holes in the layout to indicate pin one of the component, a common practice. With that in mind, look at the holes for the four caps in the middle of the pcb and then turn over the pcb to the side with the ground plane. Two of the caps have pin one connected to the plane, the other two do not.
This implies a symmetrical power supply.

Looking at the left of the pcb, I can't help but think this is based around the LM317 and LM337, both of which have adj on pin one, but input and output are swapped. This also seems to be the case in the layout. The adjust pins connect to two of the connectors, perhaps for off-pcb potmeters.

But I might be totally wrong, I have no clue what the three pin part right in the middle on the left is for that connects to both assumed-to-be-regulators...

Last edited by jitter; 11th December 2011 at 06:40 AM.
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Old 11th December 2011, 03:28 PM   #10
paulb is offline paulb  Canada
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Good guess jitter. The IC is an LT1010, used in an ill-fated attempt to have a supply splitter as part of the design (for use with single-polarity DC wallwarts). However, I found it to be really expensive so can't see it to be of much use.
As it is the board is for use with an AC wallwart or transformer. I made a few copies for general use and gave one to Greg a few years back.
Hey Greg, I can give you the user guide for the P3A as well if you like.
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