fuse replace for Apple //C monitor

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fuse replace for Apple //C monitor

Where is the fuse located on an Apple //C  9 inch monitor?  I took a look inside and could not figure out where the fuse is. Thanks for any help.

Walt

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Do you have the hitachi or

Do you have the hitachi or samsung version? (read the label on the tube). Seems the Hitachi is the more common one, its inside somewhat behind the  power button switch, sometimes wrapped in clear vinyl with a zip tie. The samsung? Possibly on the analog board, I forget.

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I have pics from when I

I have pics from when I partially disassembled mine to try and figure out what it would take to recap it. I don't have any clear shots of the label on the tube to tell which one I have. But I do see two fuses mounted on a power board that sits behind the neck board. 

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nick3092 wrote:I have pics
nick3092 wrote:

I have pics from when I partially disassembled mine to try and figure out what it would take to recap it. I don't have any clear shots of the label on the tube to tell which one I have. But I do see two fuses mounted on a power board that sits behind the neck board. 

That Little PCB isnt a power board, its the AC input filter board. It should have one fuse and two FILM filter capacitors (usually a redish brown color). You say yours has two fused? First I have seen on that tiny board, show a photo.

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Verault wrote:nick3092 wrote
Verault wrote:
nick3092 wrote:

I have pics from when I partially disassembled mine to try and figure out what it would take to recap it. I don't have any clear shots of the label on the tube to tell which one I have. But I do see two fuses mounted on a power board that sits behind the neck board. 

That Little PCB isnt a power board, its the AC input filter b

 

No, I know the difference between an AC filter and a DC powersupply.  It is the power supply board I'm talking about.  It has the rectifier diodes and the main DC filter cap.  The AC filter board you are speaking of with the two film caps and a ceramic cap is mounted right below the power switch.  It has no fuse on it.  Here is a close up of it with the switch removed.

 

 

 

The power supply board is mounted on an L shaped metal bracket that forms part of the top and back metal shielding, causing the components to sit right behind the neck board.  In the photo below you can see the orange/brown film caps you are talking about below the power switch in the upper left.  The board I'm referring to is at the bottom of the photo, and is now rotated 90 deg so you can actually see it.  There is a fuse on the left side of the board behind the black wire.  And a second fuse off to the right of the main filter cap.  Looks like maybe the left fuse is on the AC line, and the right on the main DC supply.  Without tracing it out, I'm not 100% sure.  And the only service info I've found is the SAMS photofact, and that chassis looks nothing like mine.

 

Apple (or whoever designed this for them) really stuffed 10lbs of crap into a 5lb bag.  The transformer (which is mostly out of the picture, but you can see part in the lower left) mounts on the left side behind the power switch.  I'd like to get this recapped at some point, but I always get stuck not too much further than this whenever I get the courage to try disassembling it further.  It's my childhood monitor, so it has a lot of sentimental value.  I also know it has a lot of mileage on it.  Due to that, I'd like to see it last another 37+ years.  But this one might be past my skill level.  And finding anyone local who still works on CRTs is futile at best.  At least unlike the AppleColor IIc monitor, they used all Nichicon caps here.  So I'm not as worried of them failing as the no name Chinese caps they used in the color monitor.

 

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I just noticed if I zoom in

I just noticed if I zoom in on the CRT label in the previous large picture, you can make out the letters "CHI" near the upper left of the power switch bracket.  So this must be a Hitachi monitor.

 

In a different picture I have, there is a sticker on the back side of the L shaped shielding that holds the DC power supply board shown in the previous post that says "Jul 11 1984".  So this would be one of the earlier revisions, given I believe the //c came out only a short while before that.  Which lines up with my //c being a 255 that also has the original "bad" timing circuit for the serial port.  In that same picture it also lists the two fuse specs.  And it looks like my guess that one is AC and one is DC was correct.

 

 

 

 

 

 

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2c monitor fuse a.o.

I recently opened up some as i am partly selling off my collection. I actually started with the 2c's i had for over 30 years.

 

First one seemed fined, but after a bit the monitor started smoking and turned blank.

So opened it up. Mine are all different type than what person above made photographs of. Maybe bc i am in NL/Europe.

So i located the fuse on the little board where your main leads run to. It is, with the front of the monitor standing normal upright position, facing away from you, in a vertical position in the bottom left corner.

Its quite a hassle to take that print out. But you can see the fuse right on top of that little board.

First remove the connector to the 3 pin chip connected on the outside of the metal frame. Loosen some screws and connectors (mark them) to take the board out.

I noticed the big capacitor there had blown. Ordered another one, put that in, together with a new fuse and it worked fine.

 

Booted my Kaypro and that one also started smoking... same capacitor... over the 2 main leads.

So i was wondering why these blew and then realised they have upped the mains here since 1990, gradually from 220V to 230V~

Went back to the 2c monitor and checked those capacitors again. According to schematic they would/should be 400V, but in all these they are 250V~ (same in the Kaypro)

The mains have a tolerance of +6%, which means an operational peak of 230+14 = 244 V~ is normal. If the capacitors tolerance is then down, it will blow.

So i have to check ALL psu's, possibly replace all these capacitors (which are filter out)

 

For anyone in NL (possibly other European countries aswell); check if your V has been upped, bc then you will have same problem.

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Lowlander wrote:Booted my
Lowlander wrote:

Booted my Kaypro and that one also started smoking... same capacitor... over the 2 main leads.

So i was wondering why these blew and then realised they have upped the mains here since 1990, gradually from 220V to 230V~

Went back to the 2c monitor and checked those capacitors again. According to schematic they would/should be 400V, but in all these they are 250V~ (same in the Kaypro)

The mains have a tolerance of +6%, which means an operational peak of 230+14 = 244 V~ is normal. If the capacitors tolerance is then down, it will blow.

So i have to check ALL psu's, possibly replace all these capacitors (which are filter out)

 

Hi Lowlander,

 

I do not believe the high failure rate of the filter capacitor is related to the voltage change in your country - these capicitors are notorious for failing regardless of any voltage change.

 

What tends to happen is that the electrolytics inside the capacitor dry out with age and disuse. Then when you turn on the power after years of sitting in storage, the caps explode and you get the dreaded smoke/smell (jeez that stuff stinks!). I've had at least 3 //e power supplies have the mains filter capacitor all fail in the same way (at least I took the 2nd and 3rd ones outside prior to testing!). The power supplies will usually function fine without these filter caps present, but as they are easy to source replacements for, your best bet is to replace them.

 

Cheers,

Mike

 

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Paper foil, not elco

The line filter capacitors are not electrolytic: they don't contain an electrolyte, at least not when they are made and installed. What makes them fail is the outer case becoming brittle and weak, accelerated by ozone inside the equipment. As it cracks and lets moisture inside, the capacitor (made of paper and metal foil) absorbs it and swells up, further breaking the case. Since the paper is not meant to become moist, it soon loses its insulating properties and goes conductive, which leads to rapid heating since it is across the line (120V or 240V). Most go on to catch fire or explode.

The smell is very pungent and reminiscent of burning hair, so the smoke likely contains amines.

Only particular capacitor designs that use paper separators fail like this. The most widely seen are RIFA X-class capacitors, and Schaffner filter modules. Replacement with polyester film capacitors (such as Wima) won't share the failure mode.

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To V or not to V?

Indeed not electrolytic capacitors, but paper/metal layered ones usuallly. Still smells horrible though. Very penetrating odor, that seems to linger in your nose way longer than the smoke is there.

 

Of course time and conditions for that period is a reason of failing, however, from the dozens ive done last 2 months, only the 250 V types have blown. None with higher values. And always those that are over the mains. (Also known indeed as RIFA caps) Computers indeed work fine without them, as it does not affect the computer at all. They filter outgoing noise on the mains from the switched psu. (or so i read recently anyway)

In the photographs above, you can see them in the first one; the 2 (probably in parallel) brownish big caps on the separate little board (with a ceramic cap in between, probably in parallel with a resistor). Normally these are preceeded by a fuse in one of the main lines, but these dont have that for some reason.

 

So since its so far solely those that blow and only the 250V types, im thinking the increased V of the mains is a culprit. 244V over a 250V cap with a tolerance of (?)

I had one cap fail in an apple 2e so far that was not such a Rifa cap, but one on a mobo over the 12V supply line. A 25V 10 uF. So all in all they seem to stand the test of time pretty fine so far (knock on wood).

Also ive not had a single electrolytic cap that was bad on any of the devices. I always look for cracked rubber (if its visible at all), bulging tops and fluff and acid on the board, but not a thing yet! The only fluff ive found on them was put there to stop them from vibrating.

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robespierre wrote:The line
robespierre wrote:

The line filter capacitors are not electrolytic: they don't contain an electrolyte, at least not when they are made and installed. What makes them fail is the outer case becoming brittle and weak, accelerated by ozone inside the equipment. As it cracks and lets moisture inside, the capacitor (made of paper and metal foil) absorbs it and swells up, further breaking the case. Since the paper

 

Yep, I stand corrected about the internals of these capacitors! (I probably should have known better if I thought about it some more, lol) But my main point still stands - these are notorious for failing in old hardware.

 

And yes, burning hair is probably a pretty close approximation to the smell. If you "release the magic smoke" indoors, expect to have that room smell for at least a day or two.  :-)

 

Yes, I believe the //e line filters are the RIFA X-class (X2 from memory).

 

Cheers,

Mike

 

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