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psipsyAt work, there was an old (1987 vintage) S-VHS VCR that was about to go out for electronics recycling. I asked my boss if I could have it, and he approved, so into my car it went. I get it home, hook it up, plug a tape in, and it won't load the tape. I figure it probably needs new belts (easier said than done), so I disconnect it and put it away for future repairs, having already started to lose some of the screws.
Then, I plug the LD player back in as I borrowed some of the cords, and I turn it on and... Nothing. No power. I take the cover off, and find there's a small fuse tucked away on the power supply board, and it's obviously blown. Of course I don't have an exact spare, and if I did, that would have blown immediately too because the SIDAC (a type of diode assembly for surge suppression) was shorted out.
How they work is that as a pair of diodes, they block voltage in both directions, up to a point. They can block standard line voltage, but if a surge comes through, and it's high enough, then it can overcome the breakover voltage, and they conduct, so all the extra angry pixies get directed right back out through the neutral line instead of into the rest of the unit. As the current rating of the SIDAC is higher than the fuse, the fuse then does its part and dies in an act of heroism, so that any subsequent surges don't get through. Sometimes the SIDAC survives, sometimes it doesn't, like this time.
I didn't immediately know it would be that diode, but a search of a forum for LD players suggested simply cutting out the affected diode and using an external surge protector. Well, I already am, and it still cooked itself, so I figure I might as well replace it properly. But which one? So yeah, remember when I said I found a service manual for this thing? And how it came with schematics? Yeah, that came in handy.
To an extent. The original part listed in the schematic was listed as non-stocked everywhere and didn't quite match the one on the board. Fortunately, I was able to figure out the parameters and then find something similar.
A few mouse clicks and a few days later...
Installing the parts into the power supply board, reassembling the whole thing, and putting back all 25 screws didn't take very long. Lo and behold, it works! The parts themselves cost less than $2 (not including shipping). More like $1 because there was a price break at 10, so I now have extras. Does that mean I'd do that for anyone for $1? Not really. The total cost is far more than that, because it doesn't include the value of time in research and troubleshooting, the tooling and equipment required, knowing which parts to replace and how to replace them. That's what makes such repairs expensive.
It was a big relief to find that's what fixed it. The only way to get replacement sub-assemblies for these now (such as boards, displays, motors, laser diodes, etc.) is to find a similar unit and use that for parts, hoping it's the same part and hoping something else is what killed the donor unit.
And so, I celebrated by watching some anime on LD once again. Oh, and it shouldn't do that again but if it does, I'm modifying the board to make the affected parts easier to replace, so I only have to remove 5 screws instead of 25.
Meanwhile... When I placed the order for the diodes and fuses, I also bought a PICKIT-4 and some microcontrollers to play with.
Then, I plug the LD player back in as I borrowed some of the cords, and I turn it on and... Nothing. No power. I take the cover off, and find there's a small fuse tucked away on the power supply board, and it's obviously blown. Of course I don't have an exact spare, and if I did, that would have blown immediately too because the SIDAC (a type of diode assembly for surge suppression) was shorted out.
How they work is that as a pair of diodes, they block voltage in both directions, up to a point. They can block standard line voltage, but if a surge comes through, and it's high enough, then it can overcome the breakover voltage, and they conduct, so all the extra angry pixies get directed right back out through the neutral line instead of into the rest of the unit. As the current rating of the SIDAC is higher than the fuse, the fuse then does its part and dies in an act of heroism, so that any subsequent surges don't get through. Sometimes the SIDAC survives, sometimes it doesn't, like this time.
I didn't immediately know it would be that diode, but a search of a forum for LD players suggested simply cutting out the affected diode and using an external surge protector. Well, I already am, and it still cooked itself, so I figure I might as well replace it properly. But which one? So yeah, remember when I said I found a service manual for this thing? And how it came with schematics? Yeah, that came in handy.
To an extent. The original part listed in the schematic was listed as non-stocked everywhere and didn't quite match the one on the board. Fortunately, I was able to figure out the parameters and then find something similar.
A few mouse clicks and a few days later...
Installing the parts into the power supply board, reassembling the whole thing, and putting back all 25 screws didn't take very long. Lo and behold, it works! The parts themselves cost less than $2 (not including shipping). More like $1 because there was a price break at 10, so I now have extras. Does that mean I'd do that for anyone for $1? Not really. The total cost is far more than that, because it doesn't include the value of time in research and troubleshooting, the tooling and equipment required, knowing which parts to replace and how to replace them. That's what makes such repairs expensive.
It was a big relief to find that's what fixed it. The only way to get replacement sub-assemblies for these now (such as boards, displays, motors, laser diodes, etc.) is to find a similar unit and use that for parts, hoping it's the same part and hoping something else is what killed the donor unit.
And so, I celebrated by watching some anime on LD once again. Oh, and it shouldn't do that again but if it does, I'm modifying the board to make the affected parts easier to replace, so I only have to remove 5 screws instead of 25.
Meanwhile... When I placed the order for the diodes and fuses, I also bought a PICKIT-4 and some microcontrollers to play with.
