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Amazing Tektronix 2465 Repair Information
Today I was helping a friend by checking his electronic car key with my Tektronix 2440 and 2465 oscilloscopes. The car key was fed by two 3V lithium cells but no signals could be measured. The device was completely dead.
And after that I checked all smd components on that pcb with my new and very handy Mastech MS8911 smd LCR tester. All passive components were fine but the chip or the special quarts oscillator probably were defect. The chip likely had special firmware and obtaining a new key could cost my friend up to 400 euros. And repair would be just as expensive as he told me. Which was just too much for an old car and an old electronic key. And also the IR led was already missing and placing a normal led on those 2 layer pins of course showed no activity either. And the two buttons on his pcb worked very well and were the only thing that worked.
Suddenly I heard a small short bang and my electronics room was filled with a lot of smoke. My scopes still were working fine so I began to examine the other equipment by opening them. Checking them on blown components. I couldn’t find any defects so I began to suspect one of my oscilloscopes. And indeed the smell of smoked components came out of my secondhand in Texas USA on eBay bought Tektronix 2465 oscilloscope. I was very worried because the device did cost me at least 600 Euros a couple of years ago.
I already had replaced the Lithium Battery by a new one to prevent the oscilloscope from loosing his calibration firmware. And I had also replaced the old Fan by a new one that I luckily was able to find.
I knew how to open my oscilloscope by first removing the back plate. But removing the Power Board was something I never had done before on my 2465. But removing the Top plate was next of course.
Replacing the Lithium Battery, and later on also the Fan was quite easy. But removing the Power Board apparently was not! And I couldn’t find anything useful about how to disassemble the Power Board in the Service Manual either. So this repair will be a small guide on how to repair your Power board. Next photo shows the new replacement Fan that works fine in case you might look for a replacement Fan too. The Fan must be mounted with the text visible, facing the outside.
And following photos explain how to disassemble the Power board after the top plate, as shown on the first photo, is removed. And what exactly had happened to my sturdy old 2465.
The top plate was easily removed by loosening a couple of screws on the back and side and 4 on the top. The Power board is the board in the middle which is connected to the AC Voltage selector on the back and to 2 connectors in the middle and one flat cable going to the front left. And also connected with 3 long 5 pin legged copper (gold plated?) and one 3 legged plugs connected to the, also vertical placed, board on the left. And be careful with the scope crt tube that is visible on the right.
I was trying to remove the Power board but couldn’t at first as it was not only attached to screws on the transistor cooler plate and to screws on the back of the case, but also to the case by screws on the bottom board side. I stopped counting them but I made photos of all sides, no need to mention the obvious. Most of the screws are identical anyway and only 2 smaller screws on the top plate differ.
Following photo shows the 5 bottom panel screws that we also need to remove before the Powerboard with the second panel still attached to its left side can be removed. Notice the 5 red arrows. And the second photo shows the inside of the 2465 case after both boards are removed.
After removing the Voltage selector cap and all screws that hold both boards and the wires attached to it, both together can be removed by lifting the board end on the front side first. Notice the black circle in the last photo above on the right that shows why it is not possible to fully lift that entire panel straight up vertical. That is because of the Power board with the second board attached to it that still sticks into a small hole in the back plate of the case (on the left of the BNC connector).
Therefore we also have to loosen the back plate a bit by removing any tight screw which makes lifting up both boards much easier.
Only then it will be possible to extract the Power board for repair. But keep in mind that both boards are still connected to a coax cable to a connector on the back of the case. So don’t break that when removing the Power board from the left side board. See photo:
Following photo shows the left board after the power board is removed.
Following photos show the Power board and the pin connectors used to connect to the board on its left side:
Previous photo showed the 2 nuts and bolts plus the plastic black caps that hold together both boards plus screws and which also electrical separated them from touching each other unintendidly.
Next photo shows clearly how both boards are electrically connected by long legged plugs. And the earlier mentioned flat cable that is connected to the outside board.
( looking into the scope from the back like all photo shots are taken).
After I checked the component side of the Power board I immediately noticed the smelling blown open special 2X 250VAC 0.068uF capacitor. The second one (vertical blue circle position below in next photo on the next page was still okay).
And it seems that someone already replaced all now blue e-caps on the Power board component side as visible on the following photos after next photo of both 0.068 uF 2X capacitors with the now bad blown specimen on the right.
Previous photos show that the new replacement X2 0.068 uF 250 VAC now is soldered in place of the removed bad one.
My scope is repaired again with the last X2 0.068 uF 250VAC capacitor I had left. Of course I immediately ordered 20 of them marked up to 275VAC on eBay to make sure they last longer after our Power lines already changed to the higher 230VAC of today.
After this unexpected repair I luckily got the space on my ‘work floor’ back again. These devices do take up a lot of living space. So I was happy that I could put him back completely fixed on my worktable. I ask you… What other firm can claim such long operating times like Tektronix can?
By-the-way: You will need Torx T10 and T15 for this repair.
Concerning my Tektronix 2465 repair I yesterday replaced both 0.068uF 250VAC caps after I had received the ordered new 275VAC caps.
Both caps are C1016 and C1018 in the Tektronix service manual schematic on Board A2A1. And only the C1016 0.068uF capacitor had blown which also damaged the serie resistor R1016 of 68 ohm 5%.
Which also was replaced.
They protect the Diode Bridge CR1011 (600V 3A Fast Recovery type RKBPC606-12) against damage by high AC power voltages. The Diode Bridge was not damaged. My oscilloscope is happily working as new again. (48019 HRS of service in 32 years or so).
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous repair article in the below link: