Another Tek2465B A5 Board repair attempt - work in progress - Page 1
Forum section: electronics / repair

author: rodd
author_rank: Regular Contributor
timestamp: November 05, 2020, 11:37:42 pm
content: Dear all,I bought a Tek 2465BCT at Ebay.The scope was damaged during shipping and two control knobs had their shafts broken.While opening the unit to replace the pots, I used the opportunity to take a look at the A5 board, and as usual, the SMD electrolytic caps had leaked.Fortunately the corrosion seemed light no damage to the traces and just one pad lost (see picture)I unsoldered the components around the DAC and the 74HCxxx IC's washed the board with water let it dry and soldered the components back.I had to replace some smd caps and resistors, as well as two 74HC IC's.I checked the traces for continuity and found no open traces so I was very confident the repair attempt would be successful.I turned the scope on, heard the "clicks" and the leds flickered as usual but to my surprise, there was jus a "square" four div wide (see picture)The intensity, position and readout controls do not work, but the horizontal seems to work.So I do not know if there if the problem is on the A5 board or the infamous U800 has also failed.Would a broken A5 board produce a screen like the one I am seeing?Thank you for any ideas.Roger

author: Cooler Than I Look
author_rank: Contributor
timestamp: November 06, 2020, 02:59:21 am
content: That looks like the beam finder switch is stuck in. Probably a dirty or faulty switch.

author: rodd
author_rank: Regular Contributor
timestamp: November 06, 2020, 11:13:12 am
content: You got it!The beam finder switch was dirt and stuck.The scope still have problems but I have a "working display" now.Thank you very much.

author: rodd
author_rank: Regular Contributor
timestamp: November 06, 2020, 11:26:43 am
content: This is the display I can see now.There is no trace.Intensity and position controls does not have any effect on the display.Vertical gain has also no effect.Focus and Horizontal time/div are working.Any suggestions to help me move ahead?Thank you.

author: Cooler Than I Look
author_rank: Contributor
timestamp: November 06, 2020, 07:41:30 pm
content: Is it the same for all 4 channels?Have you checked all the power supply rails?You've already found a fault due to a dirty and/or corroded switch. Chances are there are others in a similar state.I'd be getting the service manual and working through the troubleshooting charts. They date from a time when documentation was excellent and truly useful.Note that I've been told that these scopes need air blowing on them when run for any length of time out of their case else you risk cooking some of the proprietary bits. U800 for one.

author: rodd
author_rank: Regular Contributor
timestamp: November 10, 2020, 08:34:56 pm
content: Hi,Have been working on the scope and came back to report the work progress.This "strange image" was a result of a stuck beam finder button.After applying some Deoxit, the scope came to life with TEST4 FAIL2.I read that this is due to the loss of the calibration constants, so I will have to replace the DS1225 NVRAM.But that would be the last thing to do since I will like to have the scope working before that.My problem now lie in the ADC reference voltages which are below their nominal value (both absolute values are around 1.1V) when the should be around 1.25V.I think I had checked all the resistors that I have removed ( the ones around the ADC) so I am lost.Any ideas of the possible causes for both voltages being below their nominal values?Thank you.