8mm Forum: Capacitor Plague

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Posted by Lee Mannering (Member # 728) on June 12, 2019, 07:00 AM:

Well that's what its usually called in the trade but I prefer
'Revenge of the Capacitors'

Been spending a happy few hours repairing another Fujiscope SD-Auto which as we know come in various disguises this being a Noris. From the outside a clean old girl from 1985 but what awaited within? A clutch of leaking Capacitors which I am seeing more and more of leaking electrolyte all over the main circuit board. Stripped the old caps out then the clean up operation takes place before replacing with new components. Then found a cracked board and so bridged that. Its a shame when what was a little used projector comes in needing so much work but after the hours she breathes life again and good to show more Betty Boops.

Always had a soft spot for these carrier bag sized projectors which we aptly nick named 'The hand bag' back in the 80's due to its small size, but with Capacitors leaking unbeknown to many owners might be worth looking inside the back of your own for signs of trouble and needing work.

Posted by Leon Norris (Member # 3151) on June 12, 2019, 10:09 AM:

This is a problem due to age! I replaced a few leaking capacitors in the Elmo machines! One good thing capacitors are not hard to replace! And they last a long time!

Posted by Steve Klare (Member # 12) on June 12, 2019, 11:00 AM:

They are unpredictable!

-a former employer of mine changed them out if they'd been sitting in Stock more than 5 years, but then again I have an Elmo machine that sat dead in the box since the 1970s and I was able to nurse those electrolytics into operation without any casualties. (First time full-voltage power-up out on the patio: I didn't want to stink up the house!)

Posted by Leon Norris (Member # 3151) on June 12, 2019, 12:32 PM:

Check those capacitors? They do leak and explode!

Posted by Steve Klare (Member # 12) on June 12, 2019, 12:46 PM:

The visuals were perfect. The capacitances took a while to come back, but they did.

-the machine's been active about a year now and all is well.

Posted by Leon Norris (Member # 3151) on June 12, 2019, 02:31 PM:

Good luck! Steve!

Posted by Joseph Banfield (Member # 2082) on June 13, 2019, 08:08 AM:

I have worked on and repaired countless Eumig sound projectors over the years and have never found a single capacitor out of tolerance, let alone one that had leaked or exploded. Even the old tube amp Eumig machines they produced in the 60's seem to always have good caps. A good thing too as those machines are hell to work on with that tube amp covering practically all of the rear of the projector but inside practically the same sized case as a later transistorized model of the 800 series!

Now, on the other hand there were lots of crap-acitors, as I call them, produced that had a bad reputation even back in the day. Good ones have always been more expensive and remain so today.

I used to restore radios from the 1920's, specifically Atwater Kent sets that used simple paper capacitors...before they started using electrolytics in the early 1930's. Surprisingly most of them are still good and if bad they tend to open instead of short circuit and that includes the low value (2 to 4 mfd) caps used in the power supplies!

Posted by Steve Klare (Member # 12) on June 13, 2019, 11:49 AM:

Early on, before I understood hum better I replaced the big electrolytic power supply capacitor on my own Eumig 800 series. If it made any difference at all it was a tiny one, and as you say: I put the old one on a capacitance bridge and it was dead on.

(It made sense before I did it!)

Posted by Joseph Banfield (Member # 2082) on June 15, 2019, 03:41 AM:

Steve, you raise an excellent point on the 800 series and hum. The 800 series used an inferior design that was not properly shielded and required a hum-bucking coil near the heads to reduce the hum to an acceptable level. The earlier 700 series using vacuum tubes with proper shielding does not have or need this coil!

Posted by Steve Klare (Member # 12) on June 15, 2019, 07:19 AM:

If nothing else, I've never seen another machine with the power transformer mounted so close to the sound head.

-that can't help!

Posted by Paul Adsett (Member # 25) on June 15, 2019, 08:48 AM:

The Elmo GS1200, and other projectors, also use hum bucking coils. The difference is that those coils on the Elmo's virtually eliminate the hum, whereas on the Eumig 800's they just reduce the hum. And, of course, Steve is dead right about the proximity of the power transformer to the sound head. On the later Eumig 900 series the transformer is located much further away, and presumably the RFI varies inversely as the square of the distance.

Posted by Steve Klare (Member # 12) on June 15, 2019, 10:19 AM:

Someday when I’m in the mood for an experiment I should demount the transformer, swing it away and see if the hum goes down.

(-wearing my insulated gloves, too!)

Posted by Maurizio Di Cintio (Member # 144) on June 17, 2019, 04:03 AM:

Steve, maybe you should try to build an external power supply unit to feed the projector with the right voltage and DC current....

Posted by Steve Klare (Member # 12) on June 17, 2019, 07:45 AM:

I think that could work, but I dealt with it the other way: when I run my projectors through an amp I have a 60 Hz. notch filter between the machines and the amp. Even though my Eumig is the hummiest of the bunch, it reduces the hum down to ignorable levels.

My old friend Tim Christian was a pretty devout Eumig man. He decided he liked the hum!

He said it was useful because that's how he knew everything was working. He was right about that: when I start up I always turn up the volume really high. If I hear no hum it means something is disconnected or un-powered.

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