Capacitor ID on 1970's Olympus Microscope

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Stevegan

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I have just rebuilt an Olympus microscope and the last bit is the electrics for the lamp which has a 6v 15w tungsten bulb. The circuit just varies the voltage to the bulb between 2.5 and 9.5v. As you can see from the pictures there is an axial capacitor that has exploded and needs replacing but I'm not quite sure what it is supposed to do as I'm getting a voltage out as it is. One side is connected to the main fuse and the other side is connected to the power switch and then the voltage selector.
I'm looking for a replacement but not sure if it is 0.1 uf or 1 uf as there is a dot in front of the 1. Also I don't know if it has to be polarised as it is in an ac circuit. I've had a look on the RS website and found something close but not exactly the same. Any help would be appreciated. Please excuse my limited understanding of electronics as I'm a
mechanical engineer! Thanks.


 
Yes, it is a 0.1 microfarad at 500 WVDC. capacitor (500 working voltage direct current)
 
It's a BHC - I have had a look through all of the information on Alan Wood's website already, unfortunately most of it is for the BH2. There is very little information for the BH series anywhere, and no circuit diagram that I could find. The BH2 electrics are completely different.
 
Stevegan said:
Can anyone tell me what the function of the capacitor is?
Click to expand...
I'm not sure, and without a circuit diagram it's difficult to be sure, but there are a few clues from the pictures, and it seems to follow the basic idea of page 9 of http://www.alanwood.net/downloads/olympus-bh-2-bhs-repair-manual-lq.pdf, but really just the top part of that diagram. In that, UYPC64 is the power controller, and I can't see any equivalent of that in your circuit. Your circuit doesn't seem to have any equivalent to the transformer with the 7 V winding or the UYPC65 section.

It seems that the power goes through the switch and then the fuse. I think that the power then goes through the filter (the "Don't know what this is")

The power is then somehow controlled. I don't know how. The two variable resistors, the round one and the slider, are probably not capable of taking all the current, so there is probably a triac or something we can't see. The missing bit would be vaguely equivalent to the UYPC64 part of the diagram.

The power then goes to the inductor, the rectangular component with the red and the black wires. Then the power goes to the toroidal transformer, the large round orange thing. The other power lead from the switch is white, and it goes to the voltage selector, (round black thing with 4 green blobs) and then to the toroidal transformer. The output of the toroidal transformer is on the right, near the mains input, and goes to the lamp and also to a large red resistor. I guess that the resistor is there to give some load if the lamp blows.

I don't know if this helps, and it doesn't really answer the question as to what the capacitor does, apart from probably being part of the circuit that controls the voltage to the transformer.
 
Stevegan said:
Can anyone tell me what the function of the capacitor is?
Click to expand...
A capacitor is a storage tank that holds electricity.
I have not found that exact part. I could only find 400 volt parts. If I know more about the circuit, it might be that the voltage is not near the 500 volt rating.
 
Are you interested in rebuilding it as perfectly original as possible or to make it function as well as possible?
I assume the only electrical is a dimmable lamp. So, a "true green" LED with a very wide dynamic range of brightness (very dim) PWM would be ideal for biological samples. The human eye can see far more variations of green and even the lightest organelles within the cells can be seen when illuminated with green. On the other hand, slides prepared with malachite green dyes cannot be seen well with green light so a white light with high CRI (90-95) and 4200 to 5000k color would be great.
 
Thanks for your explanation, so the square thing top left is an inductor. I knew it wasn't a transformer as it only has two wires. So I managed to sketch out a circuit diagram today and it looks much simpler without all the jumble of wires. The capacitor is just connected between the live and neutral which explains why it's still working without it in circuit. I think you are right about the big resistor after the transformer as it gets pretty hot without a bulb fitted. There are no other components besides what is visible in the picture. The mystery grey cylindrical thing has Olympus moulded into the top and the voltage out varies with the slide resistor but it goes down with the slider on max and up with the slider at min which seems a bit odd, but then the bulb output is correct.

 
Thanks for that, you have answered my question which was - is it ok to use a higher voltage value than the original. The output to the bulb is AC so there won't be a rectifier in the grey tube - I'll have to look up what a triac is! Check out the circuit diagram I've just uploaded.
 
A triac is used in AC circuits to cut off some portion of each half-wave of an AC signal. The slider portentiometer in your circuit determines how much of the half-wave is cut off. Cutting off part of the waveform effector dims the AC bulb. This is a much more efficient way to dim rather than trying to dissipate part of the energy to another device as heat).
 
ronsimpson said:
A capacitor is a storage tank that holds electricity.
I have not found that exact part. I could only find 400 volt parts. If I know more about the circuit, it might be that the voltage is not near the 500 volt rating.
Click to expand...
Thanks for that, I've just uploaded a circuit diagram that I sketched out and the capacitor is just connected between the live and neutral. While looking for capacitors I discovered safety capacitors and read up on what they are. Do you think it could be one of those? As it is on AC, I found that a 400 volt dc capacitor is only good for 220 volts ac so I guess it would need to be higher than that. A 600 vdc one goes up to 275 vac.
 
Thanks for that, I'm trying to keep it original for now. I have a Nikon microscope that is converted to LED which is good for brightfield illumination but not bright enough for darkfield. I think it has a 3 watt LED but it really needs to be 10. I use a really high powered halogen light source and fibre optic ring light on it sometimes. The great thing about LED is that the colour temperature remains constant when it is dimmed whereas a filament bulb gets more red when dimmed. The only way round that is to keep it on full power and use neutral density filters. They are metallurgical microscopes by the way so I'm looking at solid objects not slides.
 
Thanks for the explanation, I'm slowly learning about electronics, or trying to anyway!
 
I think that there's a triac or similar under the black plastic part that is half-way up on the left side.

I don't think that there can be a rectifier because the output to the lamp comes from a transformer.
 
Diver300 said:
I think that there's a triac or similar under the black plastic part that is half-way up on the left side.

I don't think that there can be a rectifier because the output to the lamp comes from a transformer.
Click to expand...
I wrote that when I hadn't seen the circuit diagram. With that it seems clear that the grey cylinder is the power control device.
 
Stevegan said:
I discovered safety capacitors and read up on what they are. Do you think it could be one of those? As it is on AC,
Click to expand...
"X" and "Y" capacitors are built to sit on the power line. They will work very well and are common. I don't see why the value is important. If you find one bigger it will be fine.
 
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