I depopulated the PS board. All components test passable with one exception: One of the 1000uF Roedenstein output caps measures 19 nF
@NareshBrd
Thank you for your post. I am of two minds about it. I guess the only way to find out is to properly test and audition the preamplifier. I do not own a bench PS at present so I'm ordering one. Then we will see what's what 🙂
@NareshBrd
Thank you for your post. I am of two minds about it. I guess the only way to find out is to properly test and audition the preamplifier. I do not own a bench PS at present so I'm ordering one. Then we will see what's what 🙂
If you're just making one board for your own use and don't need it to be an exact copy, I would suggest either finding the schematic or creating the schematic by tracing the board. Then lay out a board with modern components. Make sure the board still fits in the amp and put mounting holes in the same spots as the original board.
I doubt the charring of the board is from a single event. I bet it sat a a toasty temperature for a few decades. If you look under the transformer you can see how the solder mask has discoloured. It looks like the traces have changed colour too. That doesn't happen in a bright flash with a blown fuse.
Tom
Just thinking out loud here so don't kill the messenger. If you're making a new board I'd save space by mounting the toroid separately. I'm left wondering what it would be like to design one in KiCAD and go from there?
D-SUB connectors
Regards,
Dan
That's the thinking, using scans of the old board for templates to draw over in Kicad or EasyEDA then send to JLCPCB or the like.
Maybe take a look at this.
https://www.mclpcb.com/blog/how-to-reverse-engineer-a-pcb/
"If you’re reverse engineering a simple PCB, you can often just scan a drawing of the PCB and upload it to AutoTrace — or a program like it — to build a layout. This type of program will take the bitmap image and convert it into a vector graphic, helping you obtain the PCB’s schematic quickly."
https://scancad.net/pcb-reverse-engineering-le/
https://www.fiverr.com/electronicsmust/review-your-pcb-design
https://www.mclpcb.com/blog/how-to-reverse-engineer-a-pcb/
"If you’re reverse engineering a simple PCB, you can often just scan a drawing of the PCB and upload it to AutoTrace — or a program like it — to build a layout. This type of program will take the bitmap image and convert it into a vector graphic, helping you obtain the PCB’s schematic quickly."
https://scancad.net/pcb-reverse-engineering-le/
https://www.fiverr.com/electronicsmust/review-your-pcb-design
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Strip the components from the old PCB. Scan it or take pictures and adjust them to scale. Make a replica in any available app. Order new boards.
It is the way to go. You can do it.
When it all works you can:
Then sell your boards on eBay and recover your investment and time.
Then sell your boards on eBay and recover your investment and time.
I think it's very doable. Especially considering the wealth of assistance available here.
Thanks for the comments folks.
Designing a new PCB would be quite a bit of work, especially since it would be my first. So if I'm going to do that, I want the new PCB to be identical to the old one, for the sake of originality / resale value. If it's to create a non-original board, then I might as well grab a linear PS from AliExpress and shoehorn it into the old case.
I took a quick look at Kicad. At first glance I wouldn't expect major hurdles learning the software, but being my first project I'd expect slow progress and a lot of redo work.
Designing a new PCB would be quite a bit of work, especially since it would be my first. So if I'm going to do that, I want the new PCB to be identical to the old one, for the sake of originality / resale value. If it's to create a non-original board, then I might as well grab a linear PS from AliExpress and shoehorn it into the old case.
I took a quick look at Kicad. At first glance I wouldn't expect major hurdles learning the software, but being my first project I'd expect slow progress and a lot of redo work.
Interesting, they're talking about fast vectorizing raster images. I've dabbled with that same, uh, quest a couple of times in my career, once involving movie animation stills, another time stills from assembly / disassembly videos of servers. My experience was that it worked to various degrees, but never well enough to yield usable materials without a lot of editing and rework. I would think it would be doable with AI though.
Maybe the ScanCAD folks do just that, but they don't say. In any event I get the feeling that their stuff ain't cheap, definitely not DIY-ballpark.
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I think the circuit can be made with a better layout, using the same mounting holes.
A copy of a stupid item is still stupid.
The layout is not proper, heat sinks and capacitors close together.
Discolored main PCB under heat sinks. Means poor part selection, or cramped layout.
There must be a way to automatically draw the circuit from a scan, or go backwards from the devices used, unless they have been mean minded enough to destroy part markings.
And a schematic, if available on line, will save you a lot of trouble.
And do the math first, it may be cheaper to buy another unit from second hand market.
By the way, the lady running Krell passed away, they have suspended operations for some time, the family or management has not come up with a new CEO.
A copy of a stupid item is still stupid.
The layout is not proper, heat sinks and capacitors close together.
Discolored main PCB under heat sinks. Means poor part selection, or cramped layout.
There must be a way to automatically draw the circuit from a scan, or go backwards from the devices used, unless they have been mean minded enough to destroy part markings.
And a schematic, if available on line, will save you a lot of trouble.
And do the math first, it may be cheaper to buy another unit from second hand market.
By the way, the lady running Krell passed away, they have suspended operations for some time, the family or management has not come up with a new CEO.
Given the incredible response here I believe the next logical step is take the necessary steps to come up with a schematic. Once we have a schematic there's a chance we could come up with a better design using newer parts?
Regards,
Dan
Also we could touch base with Randy Thatcher. He makes some really nice power supplies and is an incredibly nice guy.
Regards,
Dan
Regards,
Dan
That sucker is cooked. I agree about with others about NOT using that board. Personally I'd start over with a new power supply board, but I'd want to know some requirements and other details.
What is the unit supposed put out? +/- 22 Volts at ??? Amps Is it dual mono? How many wires down the umbilical?
Are there regs on the PSU side? Are there also regs on the preamp side? If so, what are those regs or what is the rail voltage after those regs? My thought process is - if it's sending 22V out to the main box, how low do the regs drop it on the other end? If it's +/-15V then you likely can roll with 18V ish.
Is fixed 120 or 240 OK for the mains? In other words - Is that voltage switch on the PSU truly necessary?
Are there other hot spots on the preamp board(s)? In other words, is something pulling more current that it should be?
Is there a service manual available for this unit?
Looking at the pix I see an 80VA donut. That is massive for a preamp. Quick google search says this preamp draws 50W. That seems high, too. A service manual will tell the story.
Do you have some pictures of the preamp itself?
I'll say my initial thought was - Oh - 22V dual rail? My little FlexReg board can do that with 317/337 regs on it. Easy peasy. But not at 50W, and the biggest transformer you can mount on that board is 25VA. The board has holes to mount an external transformer. However the current requirements are going to be the key to this one. Especially looking at the cooking of that board and the discoloration on the heatsinks.
What is the unit supposed put out? +/- 22 Volts at ??? Amps Is it dual mono? How many wires down the umbilical?
Are there regs on the PSU side? Are there also regs on the preamp side? If so, what are those regs or what is the rail voltage after those regs? My thought process is - if it's sending 22V out to the main box, how low do the regs drop it on the other end? If it's +/-15V then you likely can roll with 18V ish.
Is fixed 120 or 240 OK for the mains? In other words - Is that voltage switch on the PSU truly necessary?
Are there other hot spots on the preamp board(s)? In other words, is something pulling more current that it should be?
Is there a service manual available for this unit?
Looking at the pix I see an 80VA donut. That is massive for a preamp. Quick google search says this preamp draws 50W. That seems high, too. A service manual will tell the story.
Do you have some pictures of the preamp itself?
I'll say my initial thought was - Oh - 22V dual rail? My little FlexReg board can do that with 317/337 regs on it. Easy peasy. But not at 50W, and the biggest transformer you can mount on that board is 25VA. The board has holes to mount an external transformer. However the current requirements are going to be the key to this one. Especially looking at the cooking of that board and the discoloration on the heatsinks.
I could not find any service literature for the KPC-7B.
Sadly Krell spent way too much time and energy guarding its service manuals and schematics.
See post #25, lmk any other pics you might like to see
Two KBU8G on the PS side is all I can see.
Nine. Four are unused. Three are tied to ground. One is +21V. One is -21V.