UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

TonyDuell · 2nd Jan 2016, 8:23 pm

I think we are misunderstanding each other...

The -150V supply _is_ critical, and it does affect the calibration of the entire 'scope. But if the 'scope has been calibrated with the -150V supply at slightly the wrong voltage then setting it spot-on with a well calibrated meter could actually make things worse.

If the -150V supply is right then the others should be too.

In any case, a slight error in any of the supply voltages (no, not a supply entirely missing due to a component failure) will not cause the problems the original poster has.

So I suggest checking the supply voltages as the first thing to do. No piece of electronics will work without a power supply. If one is missing or very incorrect in voltage then find out why. But do not at this stage adjust the -150V trimpot in the hope that it will get the thing working. It won't. And remember that +/-1V in 150V is an accuracy of better than 1%, and a lot of cheap DMMs will not manage that.

2nd Jan 2016, 8:23 pm	#14
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,215	Re: Tektronix 545 Oscilloscope fault I think we are misunderstanding each other... The -150V supply _is_ critical, and it does affect the calibration of the entire 'scope. But if the 'scope has been calibrated with the -150V supply at slightly the wrong voltage then setting it spot-on with a well calibrated meter could actually make things worse. If the -150V supply is right then the others should be too. In any case, a slight error in any of the supply voltages (no, not a supply entirely missing due to a component failure) will not cause the problems the original poster has. So I suggest checking the supply voltages as the first thing to do. No piece of electronics will work without a power supply. If one is missing or very incorrect in voltage then find out why. But do not at this stage adjust the -150V trimpot in the hope that it will get the thing working. It won't. And remember that +/-1V in 150V is an accuracy of better than 1%, and a lot of cheap DMMs will not manage that.