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  • Vintage electronics repair (cine projector)
  • zilog6128
    Full Member

    I’m reasonably up on DC (micro) electronics but not so much on this kind of stuff, so looking for some general pointers/avenues of further research! Want to get an old 8mm cine-projector working again if possible (#1 goal is not electrocute myself 😂)

    Did a bit of research last night into vintage electronics repair generally & this specifically – Bell & Howell model 635 – found a scan of the original manual (although not service manual unfortunately) but although there’s a few on eBay found very little mention of it at all so possibly not a mega popular model? In fact the only specific mention I found was on some guy’s very old-school homepage on cine-projector repair, didn’t really give any helpful specifics, I could always email him though I guess if I get really stuck!

    The power cord has insulation totally missing in multiple places so I will remove that & replace with new. The thing on the right of the pic is the power transformer, as there’s only one can I assume that the whole device runs on the same voltage (that of the bulb – 21.5v)? There’s 2 pairs of wires coming from it, the thicker blue pair (to handle the higher current from the 150W bulb!) and the thinner green/brown pair that go to the motor. Is this likely to be an AC or DC device? Ideally would like to junk the power supply/transformer entirely & use something new (and safe!)

    The bulb actually looks like it’s still in working order but if I get the rest of the machine working I’ll probably look at replacing it with some kind of LED array (possibly my Max D for testing purposes 🤪) as apparently the biggest problem with these machines is the reel jamming and then the film instantly melting due to the massive heat given off by the bulb!


    asbrooks
    Full Member

    Unless there is a rectifier it’s unlikely to be a DC motor. You could keep the motor and add a mains voltage LED driver.

    TheBrick
    Free Member

    Does the mirror power supply come straight off the transfer? If so ac . Look at the motor rings, and brush position split ring brushes opposite each other ,DC, brushes off set and rings continuous AC.

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    sharkbait
    Free Member

    They fixed an old projector on The Repair Shop.  Might give some insights.

    zilog6128
    Full Member

    Does the mirror power supply come straight off the transfer? If so ac .

    yeah I think so (assuming you mean motor & transformer!!) will double check

    Unless there is a rectifier it’s unlikely to be a DC motor. You could keep the motor and add a mains voltage LED driver.

    yeah that was vaguely my plan. Thought maybe I could use the LED array from a floodlight or something if I found something approx the right size!

    With the motor then, assuming it is 21.5V AC (is that a reasonable assumption?!) can I just power it via a new AC supply – looking online, a 24v AC CCTV supply might be the cheapest/easiest to get hold of, would that work? Not too worried at this stage if it runs slightly fast (if that is what would happen by using something slightly higher voltage)? There’s a little trimmer switch on the projector to adjust the speed slightly up & down.

    They fixed an old projector on The Repair Shop. Might give some insights.

    maybe, that show was great at first, but as it’s gone on they now show very little technical details of the actual repairs (i.e. what you actually want to see!), it’s all about the sob-stories! 🤣

    Murray
    Full Member

    If I were you I’d label each wire (1, 2, 3 etc), photograph every component / connection and disassemble. You can than make a wiring diagram.

    Assuming there’s no rectifier as others have said it’s an AC motor. Check this first!

    You can get AC variable power supplies e.g. https://www.amazon.co.uk/WINGONEER-Electronic-Regulator-Thermostat-Controller/dp/B01LXLU3SD so you don’t need to know the voltage when you start. Quality of these is low – don’t assume the insulation is any good, put it in a box.

    If you can rig up a low voltage AC power supply, you can put it across the input coils of the transformer and measure the output to get the ratio. If it’s 24v and 2.4v out it’s 10 to 1. You can then set the variable power to the right voltage for the motor. UK is nominally 230v but it used to be nominally 240v – given the age I’d use that for the calculations, so if it’s a 10 to 1 transformer set your power supply to 24v.

    Cougar
    Full Member

    Yeesh, that looks like a fun project.

    I would absolutely 100% be sending that email if I were you. Requests for assistance aside, the guy will probably be fascinated about what you’re doing and happy that you reached out.

    zilog6128
    Full Member

    Quality of these is low – don’t assume the insulation is any good, put it in a box.

    😬 I’m more than happy to buy cheap Chinese low-voltage DC electronics to mess about with, anything that plugs into the mains though I’m much happier getting something “proper” from CPC, etc 😂

    If you can rig up a low voltage AC power supply, you can put it across the input coils of the transformer and measure the output to get the ratio. If it’s 24v and 2.4v out it’s 10 to 1.

    that is a good tip thanks! I just realised I do have a 24V AC PSU I can borrow from our irrigation system as it’s not being used just yet 🤔

    UK is nominally 230v but it used to be nominally 240v – given the age I’d use that for the calculations, so if it’s a 10 to 1 transformer set your power supply to 24v.

    yeah the red wires in the bottom RH corner of the pic actually comes from a voltage selector dial underneath the machine, from memory you can select between 210-250V to account for differences in “local” voltage… I guess it varied a bit BITD, and with vintage kit like this you had to account for the difference?

    Requests for assistance aside, the guy will probably be fascinated about what you’re doing and happy that you reached out.

    yeah I will probably do that. Although given the guy’s very particular writing style, he’ll probably demand I take hundreds of photos & detail every step of my meticulous restoration, which is not really what I’m about 😂

    richmars
    Full Member

    I think that for most simple ac motors the speed is a fixed ratio of the ac frequency. Is there a rating plate somewhere? So a low ac voltage supply sound be fine, so long as everything is 50Hz, assuming you’re in the UK.

    zilog6128
    Full Member

    I think that for most simple ac motors the speed is a fixed ratio of the ac frequency. Is there a rating plate somewhere? So a low ac voltage supply sound be fine, so long as everything is 50Hz, assuming you’re in the UK.

    Thanks, yeah in the UK. I will double-check but I think the only plate on it says 200/250 AC ONLY. The PDF manual I found online though does state 50Hz.

    I think this is/was a US company (looks like they’re still around actually, at least the name is!) and most of the stuff was manufactured over there, for that market, but this is a UK specific model made in England so possibly explains its relative rarity/lack of available info.

    Murray
    Full Member

    BTW, proper vintage projectors had valve based oscillators but as this is consumer grade I suspect they’re relying on the supply being 50hz, which it normally is to within 0.2hz (frequency varies slightly when the load and generation don’t match)

    tillydog
    Free Member

    I’d be tempted just to replace the mains lead (and make sure it’s got an earth connection).

    The motor looks like a shaded pole AC motor and will almost certainly run off 240V (ish) or 110V (ish) AC – it might be a 110V tapping on the transformer for it. The only way to find out is to (carefully!) power it up and measure some voltages.

    It’ll be interesting to see if you can get enough LED power into the same space as the bulb… (pay heed to the colour rendering accuracy too.)

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