Tektronics 464 Oscilloscope help need to troubleshoot trace problem - Page 1
Forum section: electronics / repair

author: EDO
author_rank: Newbie
timestamp: February 15, 2019, 03:44:58 pm
content: Hello everybody,Need help troubleshooting a Tek 464 oscilloscope. Cant see the traces as you can see from picture. But they are visible when Beam finder is pressed, both of the channels work with Beam finder , trigger and timing works also. As you can see from picture Channel one hooked up to built in generator shows a good square wave, but its lost when Beam finder is release.I do have the service manual and the only thing checked are low voltages which are all with in spec.Any suggestions would be greatly appreciate it.

author: David Hess
author_rank: Super Contributor
timestamp: February 15, 2019, 10:15:16 pm
content: While you have the beam finder activated, test the vertical and horizontal position controls.The third function of the beam finder is to bypass the input to the z-axis (intensity) amplifier so there may be a problem with it, the unblanking signal, or the intensity control.

author: EDO
author_rank: Newbie
timestamp: February 15, 2019, 10:29:07 pm
content: Vertical and Horizontal controls do work properly, so I guess next step is to test the intensity control and the amp.

author: David Hess
author_rank: Super Contributor
timestamp: February 15, 2019, 11:01:13 pm
content: There is a procedure in the service manual for adjusting the grid bias current. Maybe the adjustment potentiometer or the front panel intensity control is open or disconnected.

author: EDO
author_rank: Newbie
timestamp: February 15, 2019, 11:13:46 pm
content: Now that you mentioned the front intensity controller is very stiff, that might be a clue to start checking there.

author: EDO
author_rank: Newbie
timestamp: February 16, 2019, 12:35:20 am
content: So this was quick, there was a bad solder joint on the intensity control pot , which was a very fast repair.Now the traces are back without pressing the beam finder.One question the traces are not very strong even in maximum intensity, is there another inter adjustment to increase the maximum intensity?

author: particleman
author_rank: Regular Contributor
timestamp: February 16, 2019, 12:41:24 am
content: Quote from: EDO on February 16, 2019, 12:35:20 amHe told you right here. BTW Tektronix service manuals are really informativeQuote from: David Hess on February 15, 2019, 11:01:13 pm

author: David Hess
author_rank: Super Contributor
timestamp: February 16, 2019, 02:25:25 am
content: Quote from: EDO on February 16, 2019, 12:35:20 amThe 464 is an analog storage oscilloscope so its brightness and sharpness suffer compared to a comparable non-storage analog oscilloscope. Not only does the CRT have extra storage elements between the beam and phosphor screen, but its acceleration voltage (8.5 kilovolts) is limited to prevent damage to the more fragile storage elements and phosphor. The 465 has an acceleration voltage of 18 kilovolts.To give some idea of the difference, my 400MHz analog storage 7834 (10 kilovolts) has the brightness and sharpness of a 100MHz non-storage large CRT 7603 (15 kilovolts) even though it has a much smaller screen size. I thought the 7834 was amazingly sharp and bright until I got a 400MHz 7854 and 500MHz 7904 (24 kilovolts) which are much brighter and sharper non-storage instruments.

author: EDO
author_rank: Newbie
timestamp: February 16, 2019, 01:08:20 pm
content: OK Thank you, appreciate the info.