Tektronix 2247A not starting


Andrey Ulyanchenko
 

Hello guys! I got an oscilloscope from ebay. When I turned it on for the first time, I received a clear image with the inscription - Replace the battery -. Great, I thought, bought a battery and replaced it. But now it doesn't start at all, the blurry image is impossible to read. (perhaps again about replacing the battery?). Maybe there will be thoughts on the direction of troubleshooting?
The ripple of the power supply has been verified and the supply voltages are correct.
Photo
https://groups.io/g/TekScopes/album?id=262436


satbeginner
 

If you have another scope, I would check the vertical deflection voltages.

Also check if the wires to the deflection plates in the CRT are still connected.

Leo


alastair.knights@...
 

Might be worth checking the resistors in the voltage divider driving the CRT focus pin. These can go open circuit causing -2kV at the focus pin and a very fuzzy display. Easy to check with an ohm meter (powered off, of course) and fix. Hope this helps.


Andrey Ulyanchenko
 

The problem has changed a bit. Sometimes there is a start. calibrated perfectly. and with warming up for about 5-10-15 minutes, the input test signal is turned off. The measurement symbols remain on the screen. Re - power on- indicates the chip 160-3493-00. startup is unstable. This is a definite problem. The output transistors heat up to no more than 53 Celsius. Please advise who could solve this problem. Added a photo (please see).


Andrey Ulyanchenko
 

‌ I continue again, there are few ideas, but still. The microcontroller was checked with a thermal imager, there is practically no heating. All loops are washed, the horizontal output stage is soldered. (Transistors and microcircuit) Significant heating only of the final stage. Who can tell why the plastic circles are installed on the top of the terminal transistors? This is plastic and does not dissipate heat? Symptoms at the moment are cold - stable confident start, after warming up for about 20 minutes, a blockage occurs, apparently from overheating. Restart is no longer available until it cools down. Added a photo of plastic * radiators *. Maybe there will be ideas? Overheating of the final stage can affect the microcontroller and turn off the oscilloscope. I would like to return the device to work :-)
‌ Add new photo. Thanks


 

Andrey,

You say that the plastic radiators "[do] not dissipate heat," but your thermal images tell a very different story. You could, of course, try replacing the plastic radiators with metal ones, and see if that does a better job of cooling those transistors.

What do those transistors do? Are they directly related to any of your symptoms?

-- Jeff Dutky


Harvey White
 

Could they be insulators?

Harvey

On 4/2/2021 6:11 PM, Jeff Dutky wrote:
Andrey,

You say that the plastic radiators "[do] not dissipate heat," but your thermal images tell a very different story. You could, of course, try replacing the plastic radiators with metal ones, and see if that does a better job of cooling those transistors.

What do those transistors do? Are they directly related to any of your symptoms?

-- Jeff Dutky