Tektronix 2467B Flicker - Page 1
Forum section: electronics / repair

author: Alfons
author_rank: Regular Contributor
timestamp: September 10, 2019, 07:15:49 am
content: I'm opening a new thread here because I need to fix something here.I already wrote in another thread. Here again briefly the summary:I purchased a defective Tektronix 2457B with Option 9 and 10. Error was, that the device turned on and off again and again. Even the smell showed that electrolyte must have leaked out. The device stank like a trash can. After I opened the device, I discovered the leaked SMD electrolytic capacitors on the A5 controller board. The traces were not attacked and also neighboring components were still OK. I checked that under the microscope. After I had cleaned everything and used new Elkos, the device worked again. The error did not occur anymore. Otherwise, I could not detect any abnormalities in the power supply, all values ​​are OK, Ripple unobtrusive.The flicker (looks like modulation of the z-Axis) occurs only in connection with the ARB function generator and only in the range between 1-10Mhz. The generator does not do more. The signal representation is otherwise first class.The flicker is independent of the position of the readout knob. But others also wrote that, who have this flicker too. It has nothing to do with the readout, it also occurs when the readout is turned off. It has a very slow frequency, anything around the 2-3 Hz, it looks like waves of a modulation. CRT is set with Cal 08.In the meantime, I have noticed that the flicker occurs at frequencies of 1MHZ and more, if the value is exactly 1MHZ, 2MHZ, 3MHZ, etc., that is set exactly to 7 digits on the function generator. So for example 5,000,000.0MHZ. Therefore, this does not occur in practice and also with analog signals. If I adjust the value by only 10Hz, the flicker disappears. So at, for example, 5,000,010.0MHZ the flicker disappears. So there seems to be something to do with driving the Z-axis, any interference.Does anyone have any idea where to start with the search? I think that is a defect, otherwise it would occur more often.

author: MarkL
author_rank: Unknown
timestamp: September 10, 2019, 04:02:12 pm
content: You could start the search by looking at the VZ and VQ (Z-axis) outputs on the A1 board (J191 pins 9 and 10) and look for variations that are synchronized to the flickering. These are also waveform test points 65 and 66 which are shown on "TEST WAVEFORM" page.Use caution - there is high voltage in this area (up to 87V) and any shorts to ground on these outputs will have you looking for a new U950.This will at least divide your problem. If you see variations on TP 65 or 66, look into something in the Z-axis driver circuitry in U950 and previous stages. Or if no variations, start looking at the CRT driver board.Maybe this is normal behavior? If you set the frequency off by say 0.5Hz, does the flickering change in rate also?

author: Alfons
author_rank: Regular Contributor
timestamp: September 10, 2019, 04:28:16 pm
content: Thanks for the hints, will try that.I have to change the frequency by about + -10Hz, so that the flicker disappears. For example: 1Hz is not enough.But it may also cause the function generator this flicker.Today I synced my old TI pulse generator via the functons generator so that I can generate stable pulses. Have no manual for the pulse generator, so I had to play around a bit. For example, if I supply the pulse generator with 3.2MHz, it gives me a stable frequency of 7,000,000,0MHz. Here then the flicker does not occur. But I provide it with, for example, 5MHz, the flicker is back.But tomorrow I have another function generator here, so that I can compare. If it does not occur, then it is actually at the function generator. Sorry my bad englisch.Incidentally, when I turn up the brightness, the flicker is hardly or not visible

author: Alfons
author_rank: Regular Contributor
timestamp: September 10, 2019, 05:32:38 pm
content: Have just checked it quickly. The interference is not visible, neither at pin 9 for the signals nor at pin 10 for the readout. Pin 65/66 are Pin9/10

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: September 11, 2019, 03:29:58 pm
content: I see the same issue on my 2467B's... have just been assuming a PS re-cap would take care of it.

author: Alfons
author_rank: Regular Contributor
timestamp: September 11, 2019, 05:00:17 pm
content: I have all Elkos lying here, but thought that a recap would not be necessary, otherwise everything works well. But if I get that fixed by a recap, I will do it.I'm just wondering why that happens exclusively with digitally generated signals. Maybe the Scope "sees" more than others because of the MCP tube?