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Post by Casethecorvetteman on Mar 3, 2016 3:01:05 GMT -5
The settings on those pots varies a bit between splitters too, out of four measured i get:
339k ( focus issues )
380k ( R762210, so lower setting was expected )
557k
325k ( focus issues )
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Post by dummyload on Mar 3, 2016 3:23:38 GMT -5
You nailed it.
Lower HV output = lower speed electron beam = less force is needed for same deflection = larger raster and high midpoint focus setting with yoke needing to be way back.
Higher HV output = higher speed electron beam = more force is needed for same deflection = smaller raster and low midpoint focus setting with yoke moved hard forward against deflection yoke.
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Post by Casethecorvetteman on Mar 3, 2016 3:24:23 GMT -5
If we can figure out why these two splitters are causing the focus issue, there is a chance we may be able to repair them by replacing that pot. Ive got two here that are faulty in that same way, and if it is that trimpot, that could be two splitters that can be made good again. In theory, id say the adjustment process for that pot would involve a HV probe to measure actual HV output, and a multimeter to set the pot until the output to the EHT board matches the output of the HV at a 1000:1 ratio. For example setting EHT board so the HV probe reading 34.7kV, adjusting trimpot so multimeter reads 32.7v. This could involve a bit of back and forward adjusting between that pot and the EHT P1 pot until the desired outputs are obtained, but id expect if the output to EHT board is what the SEOS manual says, and the HV probe reads 34.7kV, then it should all be correct. I cant really see any other practical method to make these adjustments, but if anyone else has any ideas on a possible method id be interested to hear them  |
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Post by Casethecorvetteman on Mar 3, 2016 3:26:27 GMT -5
You nailed it. Lower HV output = lower speed electron beam = less force is needed for same deflection = larger raster and high midpoint focus setting with yoke needing to be way back. Higher HV output = higher speed electron beam = more force is needed for same deflection = smaller raster and low midpoint focus setting with yoke moved hard forward against deflection yoke. Thanks mate We are making progress here then! |
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Post by dummyload on Mar 3, 2016 3:29:08 GMT -5
Those settings will vary anyway ,in the potting are the hv resistors these are not precise ,this is why a trimmer is needed for compensation ,and I think these hv resistors go bad in the potting.
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Post by Casethecorvetteman on Mar 3, 2016 3:32:52 GMT -5
Those settings will vary anyway ,in the potting are the hv resistors these are not precise ,this is why a trimmer is needed for compensation ,and I think these hv resistors go bad in the potting. Thats probably likely too, do you think the resistors will fail and cause raised HV or lowered HV? |
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Post by Casethecorvetteman on Mar 3, 2016 3:43:16 GMT -5
With the fact this splitter with the focus issue has a lowered HV output, yet the feedback reads 33.5v, id have to think the fault is in the sensing circuit somewhere more so than the actual HV components of the splitter.
It appears as though the splitter feedback is telling the EHT board that the HV output is higher than it actually is, thereby causing the EHT board to lower the HV to well under 34.7kV
If the internal HV resistors in series with the HV outputs were to fail, id expect the feedback to still adjust the HV and probably still reflect the actual output voltage in a simular way?
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Post by Casethecorvetteman on Mar 3, 2016 5:08:47 GMT -5
Trying to figure what connects to what here what comparing to the diagram,
Black wire leaves potting and connects to feedback coax via 2700k resistor.
Middle pin leaves potting and connects to ground, also connects to left side of trimpot.
Other pin leaves potting and connects direct to feedback coax, on the diagram i believe there is an internal resistor connecting it direct to the HV feed line, prior to the individual resistors on each output. Cant seem to work out the value of that one through measurements.
Right hand side of trimpot connects to feedback coax via 560k resistor.
Ground -> trimpot -> 560k resistor -> feedback coax.
Lowering trimpot value should lower feedback voltage, which should raise HV. ( that follows true with the R762210 splitter, which had higher than normal HV )
Whatever the value of the resistor between the HV and pin connected direct to feeedback is unknown, and im not even certain if it is the resistor.
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Post by dummyload on Mar 3, 2016 6:01:51 GMT -5
The eht board drives the quad until it sees 33,3v at feedback point, so adjusting the trimmer on splitter will not change the 33,3v feedback value but hv output (because you change the 1/1000 value)
So if you have a splitter issue you must can measure hv output no way around .
Why you have 33,5v with that splitter ,not sure but feedback is to high for sure ,maybe arcing on feedback resistors in potting ,making extra noise on feedback point making you're multimeter show 33,5v or there is an oscillation?
Scoop on feedback point can help in that matter , but make sure to use probe 1/10 to have scoop load at 10mohm ,the normal probe 1/1 1mohm input will make the hv output to high , 10mohm does it rise with about 1,2kv)
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Post by Casethecorvetteman on Mar 3, 2016 7:58:11 GMT -5
So with that said, what options could there be to fix these splitters?
Does the feedback voltage go back through P1 on the EHT?
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Post by dummyload on Mar 3, 2016 10:36:14 GMT -5
See nothing for the moment I'm afraid.
Seems I used the term reference (feedback point splitter) a bit wrong, the real reference value is made on the eht board and set by p1.
With p1 on the eht board you adjust the eht reference value at compator I3 witch compares with the hv feedback value ,
p1 determines what the value of hv output will be and consequential what the feedback value will be.
So value of 33,3v at feedback point will chance adjusting p1.
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