Sankyo 700 Fuse ?

[Andrew Sterling]

Hello all. Does anyone know if there is a main fuse in the Sankyo 700? I have a unit that does not power on. I have seen photos in the forum of 600 and 800 where you can clearly see it on the circuit board. But On the 700 I don't. Thanks!

[Steve Klare]

If you look on the ratings label and it has makings like "UL" and "CSA", it has to have main fuse somewhere. These agencies certify that a device will protect users from electric shock and prevent building fires and a main fuse plays a role in both of these.

[Brian Harrington]

Can you perhaps post a pic with the back cover off? Van Eck's pics do not show the cover off. I have the 702 model and it is clearly visible, but without seeing the 700 I can't say for sure.

[Steve Klare]

It should be pretty close to where the power cord enters the chassis. It’s supposed to be the first thing wired to the “hot” side of the cord.

[Brian Harrington]

Found this pic on the old forum, but it is not visible. Perhaps they buried it on the PCB somewhere.


I've found from working on projectors for years, that the manufacturers did some, let's say, "interesting" things. Usually the part you need to fix or replace is buried behind parts that never wear out and never need to be fixed! Belts that should be easy to install often are not -- but that's a different story for a different day!

[Brian Harrington]

Any luck, Andrew?

[Andrew Sterling]

So I dove in and took eveything out of the unit. Can not find a fuse any where. I'm going to figure out if there is a short around the big caps where the power enters the circuit board and check that power transistor on the lower right. The black and yellow switches on the upper right are switching on and off after doing a continuity test on them. If anyone has any ideas or experience in this unit let me know.
Thanks
Andrew

[Brian Harrington]

I'm not trying to facetious, but perhaps the lack of a fuse is why it doesn't work.

I've found that different machines have different ways of installing a fuse. From the picture, I don't see an obvious place where it is supposed to be though. Very strange that Sankyo would have built this without a fuse since they did with most of their other models.

This guy had the same problem, but it's a dead-end thread: https://8mmforum.film-tech.com/cgi-b...c;f=1;t=009691

[Steve Klare]

This is interesting. It's a very similar looking Sankyo 501 from the Van Eck website and it's got four fuses mounted in clips near the inlet. I'm not even sure what this means since the soldering on the fuses doesn't look very professional.

There are fuses that look like capacitors that are mounted on printed circuit boards, but I don't think I've ever seen these used for safety purposes: basically just to limit the damage to the board if a component shorts since the main fuse would pass too much current. (Could it be? ...maybe!)

If the main fuse is there it should be locatable something like this: find the black wire coming off the power inlet and find whatever it connects to at the far end. Ideally it should be the fuse itself. If it connects (for example) to a PC Board, the board's trace the black wire connects to should go directly to the fuse (or fuse clips). The idea is whatever conductors exist between that inlet and the fuse don't have the fuse's protection and if they short to case, the only protection will be the fuse or circuit breaker in the house wiring service panel, which can pass a lot more current and cause a lot more mayhem. The best thing to do is keep this internal path as short as possible.

I have seen line cords with internal fuses, but I don't think they would ever be a removable type.

This 501 has a VDE mark on the back panel, which is a German safety agency. Before these hit mass production, VDE would take first article units and introduce short circuits inside and make sure nothing worse happened than popping a fuse: no melting power cords, no 240VAC showing up on the case to kill a film collector (There are few enough of us as it is!). Being of similar vintage the 700 must have endured something similar.

If I were to wire this thing up, I'd do something like this: We have that main transformer there with all those taps "100V, 110V, 117V, 125V,...240V". Transformers develop short circuits, so I definitely want my main fuse between the inlet and that transformer. We also have that selector switch with those same markings: "100V, 110V, 117V, 125V,...240V". We want each of those transformer taps to run to the appropriate contacts on the switch. Normally I'd want the main fuse to be between the wiper for the switch and the inlet "hot" terminal since now we have both a direct connection between the inlet and the fuse and a fuse in-line regardless of the input voltage selection.

It can't be in-between the "0V" terminal of the transformer and the Neutral side of inlet because all the "Hot" side stuff will be unprotected by blowing the fuse and it will be quite dangerous.

The main fuse located anywhere on the other side of the transformer won't do a thing if the transformer itself shorts, so it's got to be somewhere up front if it's anywhere at all.

(Just saying...)