Waterman PocketScope Antique Oscilloscope Repair - Page 1
Forum section: electronics / repair

author: Bobajake
author_rank: Contributor
timestamp: June 30, 2015, 02:04:54 am
content: Okay this is a new one for me...I'm 16 so I am new to this and I need some help.I have a waterman pocketscope s-10-a (i'll link in schematic down below) and the vertical deflection does not seem to work at all.The pictures I attached are pictures of me inputting a 9 volt 60hz sine wave (I double checked this with my working scope) andall I get is what you can see in the pictures.I'm thinking that it is the vertical deflection tube (shown in the picture), but when I remove the tube completely, there is absolutely no vertical deflection. Even worse than what you can see in the pictures...My Question Is, Can a Tube like that (a 6au6) only partially work?Sorry about the horrible picture cropping job I needed to cut down the size of them...Link to the schematic:http://www.electronixandmore.com/misc/images/watermans10a.pdf

author: poot36
author_rank: Frequent Contributor
timestamp: June 30, 2015, 05:10:05 am
content: I would start by checking that all of the power supply voltages are correct and then test all of the capacitors in the vertical section as well as the resistors. Make sure to discharge all of the big capacitors before testing anything in the scope there is high voltage in any tube based circuit (unless it is a voltage measurement)!!! The capacitors will not usually self discharge (unless they are leaky) because the vacuum tubes act as a great insulator as apposed to a semiconductor based scope. You can test the tube for shorts with a multimeter on ohms mode but this will not tell you about the life left in the tube. If you want to know that you will need to get a tube tester. Once again any tube based device has high voltage (some of them 450V DC for the tube plate voltage and the high voltage (but low current) CRT anode is usually 2000 V DC and up in it and can kill you so be careful!!! Also try cleaning all of the switch contacts including the time division switch and the input voltage select switch and all of the variable resistors.

author: Bobajake
author_rank: Contributor
timestamp: June 30, 2015, 12:37:20 pm
content: The previous owner appears to have replaced all the caps, but ill check them anyway. and how should I go about checking the tubes? look for short circuits? low resistance? ect...

author: poot36
author_rank: Frequent Contributor
timestamp: June 30, 2015, 01:22:58 pm
content: The proper way to test a tube is to get a tube tester. You should be able to pick one up for around $50 or so. If the schematic has voltage test points for the various tubes you can use them to determine if there are problems with the tubes or not. Have fun and stay safe.

author: Fraser
author_rank: Super Contributor
timestamp: June 30, 2015, 02:19:18 pm
content: I tend to buy a full set of spare valves (tubes) for my thermionic era equipment. Most has now gone to new homes though. Russia is still a rich source of such valves. You may wish to consider buying some rather than buying a valve tester which is usually quite bulky ! You can then change out valves to see if it improves performance.Aurora

author: Bobajake
author_rank: Contributor
timestamp: June 30, 2015, 02:37:46 pm
content: Thank you both poot36 and Aurora, i think i am gonna bu spare valves, they are less bulky and I think altogether cheaper than the tester.

author: oldway
author_rank: Super Contributor
timestamp: June 30, 2015, 05:05:07 pm
content: I sincerely believe that it is not worth the effort, nor the risk.The price of the valves may exceed the value of the unit.That is a museum piece that has no interest.There are also hazardous, even lethal voltages in this unit.Try to buy a simple and cheap working oscilloscope hung chang model OS620...