Hi,
I checked the zener spec. and found that the minimum current for the zener it is 2 ma. means that the 309/15000 =.0206 the current it is within tolerance. Also found that the voltage range it is 156 volt to 171 volt. Means that the output it is within zener specification. What you can do is to get some combination of zener diode voltages that give you voltage close to 160 and 260 volts. I think that there it is not a problem with the voltages you are getting. I agreed with what davidsrsb suggested in thread 17.
I checked the zener spec. and found that the minimum current for the zener it is 2 ma. means that the 309/15000 =.0206 the current it is within tolerance. Also found that the voltage range it is 156 volt to 171 volt. Means that the output it is within zener specification. What you can do is to get some combination of zener diode voltages that give you voltage close to 160 and 260 volts. I think that there it is not a problem with the voltages you are getting. I agreed with what davidsrsb suggested in thread 17.
Well I had some progress that I would like to share.
I used 2x75v zeners and I got voltage down to specs ,so i started troubleshooting and I found a nearly shorted 1uf/40v tantalum cap that looked perfectly fine but it read as 560 Ohm resistor.
It seems that this was the cause of the overvoltage , after replacing it the voltage dropped a few volt down, probably if i put back the Z160, it will be within specs.
Unfortunately the oscilloscope is not working right yet.
I get no trace, just a dot in the center of the screen.
Obviously the horizontal amplifier circuit is in fault, I took some readings and I am getting 250V on the x-plate instead of 135V. I have disconnected wires X1 and X2, isolating Z-board from X-board but nothing changed. I thought that it would be probably a faulty transistor but all transistors on Z- board test ok.
here are the schematics :
Is the problem coming from the X-board?
What voltage should I expect at X1 & X2?
D1 & D2 are connected to the back of the crt, please dont tell me that I have a faulty screen. :/
Any thoughts ?
Thanks
I used 2x75v zeners and I got voltage down to specs ,so i started troubleshooting and I found a nearly shorted 1uf/40v tantalum cap that looked perfectly fine but it read as 560 Ohm resistor.
It seems that this was the cause of the overvoltage , after replacing it the voltage dropped a few volt down, probably if i put back the Z160, it will be within specs.
Unfortunately the oscilloscope is not working right yet.
I get no trace, just a dot in the center of the screen.
Obviously the horizontal amplifier circuit is in fault, I took some readings and I am getting 250V on the x-plate instead of 135V. I have disconnected wires X1 and X2, isolating Z-board from X-board but nothing changed. I thought that it would be probably a faulty transistor but all transistors on Z- board test ok.
here are the schematics :
Is the problem coming from the X-board?
What voltage should I expect at X1 & X2?
D1 & D2 are connected to the back of the crt, please dont tell me that I have a faulty screen. :/
Any thoughts ?
Thanks
Last edited:
The X amplifier is an oddly drawn long tailed pair. The final supply is 250V, so the two BF258 are sinking zero current. The BC237 is the tail current source.
I would expect about 2.5V across the 150R, +7V on the tantalum +ve
Also what voltage on X1 and X2?. They should be around 0V and certainly between +/-12V
I would expect about 2.5V across the 150R, +7V on the tantalum +ve
Also what voltage on X1 and X2?. They should be around 0V and certainly between +/-12V
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