Tektronix 7633 Oscilloscope Repair - Page 1
Forum section: electronics / repair

author: KWKolb
author_rank: Contributor
timestamp: April 22, 2017, 03:13:27 pm
content: I am about to embark on a repair of my 7633 and was hoping someone could help point to the cause. I have both the Operator's and Service Manuals on hand.The display shows anomalous traces. Also, the scope makes a faint intermittent buzzing noise when warming up. The fan slows while the scope buzzes. The buzzing and traces occur with or without plug-ins installed. The traces change somewhat depending on the time base setting. Pictures below showing two different time base settings and with plug-ins removed.Thank you in advance for any assistance you can provide.

author: tecman
author_rank: Frequent Contributor
timestamp: April 22, 2017, 05:26:14 pm
content: Likely power supply electrolytic caps. Known problem as they age. Replace them all.paul

author: David Hess
author_rank: Super Contributor
timestamp: April 23, 2017, 07:50:51 pm
content: I agree about the aluminum electrolytic capacitors in the power supply.Start with the procedure in the service manual for checking the low voltage power supply outputs for level and ripple.

author: KWKolb
author_rank: Contributor
timestamp: April 24, 2017, 03:21:23 am
content: I checked the voltages and the -15v supply looks almost sawtooth-like. That points to a 14,000 uF, 25v cap. If I can find them, I will replace all seven of the big power supply electrolytic.Now the question is where to purchase large electrolytic (largest is 18,000uF at 15v) in onesy-twosy quantities at a good price.Respectfully,Kevin

author: tautech
author_rank: Super Contributor
timestamp: April 24, 2017, 04:34:29 am
content: Quote from: KWKolb on April 24, 2017, 03:21:23 amI've used these guys for the less popular values:http://www.tedss.com/

author: daveyk
author_rank: Frequent Contributor
timestamp: April 24, 2017, 09:47:50 am
content: Quote from: KWKolb on April 24, 2017, 03:21:23 amMake sure there aren't any 10uf caps in the feed back or regulator control pins. I would be it's a small one rather than the big ones.I think that is the same scope I use to use in the early 1980s with a spectrum analyzer module plug-in. We used them to certify ultrasonic transducers. We used a Tektronix camera to take screen shots with Polaroid film. I see the electrical connections for it on the CRT bezel of your scope.DaveSent from my iPhone using Tapatalk

author: dave_k
author_rank: Frequent Contributor
timestamp: April 24, 2017, 11:32:20 am
content: Quote from: KWKolb on April 24, 2017, 03:21:23 amKevin,Maybe this information might help you...https://www.eevblog.com/forum/testgear/tektronix-76037613-repairs/msg743296/#msg743296

author: David Hess
author_rank: Super Contributor
timestamp: April 24, 2017, 02:27:11 pm
content: Quote from: KWKolb on April 24, 2017, 03:21:23 amUsually I end up using snap-in or leaded radial capacitors as replacements even if I have to make modifications because they are relatively inexpensive. The regulator board is held in place by screws into the chassis and does not rely on the capacitors so this will not be a problem.A suitable snap-in or leaded radial capacitor to replace the 18,000uF at 15 volt capacitor can be had for less than $5 new. Do not be afraid to use the next larger standard value like 22,000uF instead of 18,000uF if it is less expensive.

author: KWKolb
author_rank: Contributor
timestamp: April 25, 2017, 02:07:52 am
content: Thanks all. Capacitors are on order. Also ordered some metal feedthroughs to make adapter boards to mate the new snap-in caps to the Low Voltage Rectifier Board.Will update when I install the new capacitors.VR,Kevin