replacing caps. in a EICO model 460 - Page 1
Forum section: electronics / repair

author: timbob
author_rank: Contributor
timestamp: January 29, 2017, 06:36:29 am
content: I save this oscilloscope from a electronic recycling center. I replace the power cord and it turns on. I need help knowing which caps in the oscilloscope that I need to replace. I know near the power cord need to be replace because the wax or some thing is coming off them. here are the picture can not attach them in the posthttp://imgur.com/a/8oCNr

author: Seekonk
author_rank: Super Contributor
timestamp: January 29, 2017, 07:55:52 am
content: " can not attach them in the post"As a rule I never look at external sites for pictures and many others don't either. To me it is just rude making people wait to load way oversized pictures to give free advice. Every computer has some form of photoshop to reduce these pictures to 100K. Do that and they will load. You are never going to see high resolution on a computer screen.

author: SeanB
author_rank: Super Contributor
timestamp: January 29, 2017, 09:17:10 am
content: Simple thing is any tubular capacitor that is waxed needs replacing. Any electrolytic capacitor there needs it as well. Once that is done you can then run it and check the calibration is within 10% of the nominal. Any resistors that show signs of running hot need replacing as well, with ones of a higher wattage. I would also be suspicious of those carbon composition resistors, any value over 22k will invariably start to drift high with age, but in most cases that will not be much of a worry.

author: oldway
author_rank: Super Contributor
timestamp: January 29, 2017, 10:12:01 am
content: QuoteAnd it worked fine ?I would test it, check if there is correct polarisation of the tubes grid and replace something only if there is a malfunction...

author: Gyro
author_rank: Super Contributor
timestamp: January 29, 2017, 11:23:53 am
content: I agree, I'd mess with it as little as possible. The Electrolytics are large can size for their value and low stressed, at worst they've probably lost some capacitance. Modern caps of the same value will have lower ESR so put more strain on the valve rectifier. Obviously replace anything that's obviously leaking but otherwise I'd leave them alone. Likewise the resistors unless they are causing an operational problem.Give it a nice long soak test - in your presence, not unattended!It's a long time since I saw a scope that let you attach your own capacitor for custom timebase settings.P.S. What I WOULD do is put some strain relief on your new power cord and make sure ground connection to the case is nice and solid!

author: timbob
author_rank: Contributor
timestamp: January 29, 2017, 12:47:04 pm
content: Quote from: Gyro on January 29, 2017, 11:23:53 amIm going to change the power cord. Im going to put a iec connector on it, saw it on another post

author: oldway
author_rank: Super Contributor
timestamp: January 29, 2017, 12:58:51 pm
content: I started in electronics at the time of the tubes and I even manufactured tube amplifiers for musicians and Hi Fi enthusiasts.At that time, the ESR (equivalent series resistance) of capacitors was known only by the theory on the operation of capacitors.No technician or engineer was concerned with that.I repaired hundreds of tubes gears (especially televisions), I worked at that time in several repair shops andI never saw anyone measuring the ESR of a capacitor, or even heard about it.Measuring the value of the capacitance was enough.The importance of the ESR of a capacitor appeared later with the first switching power supplies.So when we talk about measuring the ESR of a capacitor of a tube antiquity like this old oscilloscope EICO, it seems to me totally ridiculous and absurd.Besides, there are many topics on this forum dedicated to the refurbishment of tube equipments that fall into the same ridiculous assestments.

author: Tom45
author_rank: Frequent Contributor
timestamp: January 29, 2017, 06:37:34 pm
content: Quote from: Gyro on January 29, 2017, 11:23:53 amIt isn't really accurate to say the 460 has a custom timebase. Or any timebase for that matter. It doesn't have a triggered sweep.I built my 460 ca. 1960. From memory it cost about $120, nearly $1000 in today's money. For comparison, a Tek 532 DC to 5 mc single channel scope was $875 in the 1960 catalog.The 460 was good for looking at signals. The 532 was good for also measuring them.