Project/one Mark 1A

jeep jones

Active Member
Hey guys, I just picked up a Project/one Mark 1A at an estate sale for 20 bucks.

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Before I got too far into cleaning, I plugged it to see if I wasted 20 bucks. The right channel is definitely toast. I deox'd everything well and it didn't come back. New fuses inside and out...nothing. Anyone have experience with these? Was the next most likely offender to take out a channel? I'm moderately good with a soldering iron, but have no schematic or understanding of where to start...

Here is a look at the boards...any visible clues here?

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Thanks in advance!
 
Is it the right channel? I saw what looks like at leased three burnt 1/2 watt resistors.
 
The second from the right big red resistor in front of the output transistor and the one right in front of it looks pretty black. A couple more on that side look discolored as well. The resistors on the right half of the board should be the same as the left half. Look for discoloration between the two halves of the board. The output transistors and small driver transistors could be damaged as well
 
Yup. Also look for discoloration of the circuit board (both sides) and other components and board structures. These are often a dead giveaway to something having been burned at the stake as well as areas that will likely become future problems if you let things go. I envy you your project. Look like nice clean, simple, yet substantial diagnosis and rework tasks, perfect as a starter project instead of a brutal bear of a basket case the guys around here battle for months.
 
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Ooo, yeh...that one does look like toast. Awesome info, Thanks guys. I will dig in and try to be a full assessment.

One question though, can I replace with similar specs or does brand/manufacture matter?
 
Yes, you want to replace failed (or poor-performing) components with ones of the same or better value, rating, and performance. That said, many people spent a lot of time DESIGNING your receiver and they knew what they were doing in specifying the components used. You need to base your investigation on their intent by finding a schematic that will show all component values and the connections between them. Then you will want to compare the components actually in place on your unit with those shown in the schematic and resolve any differences (it often happens that a failure, like your bad channel, has occurred before and was not properly repaired). If you're not careful, you can end up spending good money for good replacement components only to see them go up in smoke because you haven't gotten down to the CAUSE of the failure. Hope you like puzzles; you got a dandy on your hands...
 
It looks like a lot of 5% tolerance carbon film resistors. A few cents ea. in cost. A schematic with a parts list is a big help. The smaller transistors usually don't cost too much. Even the output transistors are probably about $10 or so each. Getting parts is easy. Figuring out what's bad is the fun part. But finding the service manual is the first step. Try hifiengine.com register for free and look for it and download it for free.
 
Ok, done alot of surfing and there are no schematics anywhere for Project/one anything.

Can I map the voltages from the working left channel components and use them to detemine correct voltages foe the right?

I realize that some of the left channel components may have degraded as well, but in the absence of a schematic, what else can I do?
 
Checking voltages is a good first step. I had one amp board that was so bad I wound up just shotguning the whole board with new transistors. It sounds like yours is just problems in the one channel though. Have you looked for any sites that sell copies of SAMs manuals? 《Edit》I didn't see any SAM's either,.
 
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