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| Tektronix 7633 Scope, Can anyone please help Old64goat!!! |
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| finom1:
--- Quote from: tautech on May 03, 2017, 06:23:00 pm --- --- Quote from: finom1 on May 03, 2017, 06:03:24 pm ---I just got another update from Old4goat: "This is getting OLD...LOL I did find Q1185 & C1198 on the HV schematic which I did PRINT OUT, but when I look at the HV board "picture" they are NOT shown. I spent two hours looking at the pictorials & schematics and printed them all out. If Q1195 & C1198 are INSIDE the HV box they must be hidden and are not serviceable. Another thing is how the heck am I going to see if I got +15 volts across C1198 if it is INSIDE the HV box?" Can someone please advice on next steps to take? Thank you for helping!!! --- End quote --- This is getting to be hard work with Old4goat. I suspect the transistor he seeks is the main switcher for the HV SMPS, they are normally a TO-220 or similar and bolted to the frame or some heatsink. When this is the case it is often identified in the schematic with a dotted line indicating the device is NOT on the PCB. Service manuals are written for technicians and without knowledge of the conventions used some considerable time studying and comparing with the physical layout MUST be invested for it all to make sense. There are NO shortcuts, he must spend the time to understand the schematics, principles of operation, physical layout and reasons for it all. All we that are self taught have had to follow this path and it need be seen as an investment of time for your future. Good luck. --- End quote --- Good advice, thank you for sharing!!! |
| finom1:
Here is an update from the Old64goat: "First here is a quote from David Hess: "All of the high voltage inverter circuit including C1198 which decouples the unregulated +15 volt supply to the high voltage inverter and Q1195 which is the TO-3 power transistor for the inverter is shown in the upper left corner of schematic 7 which is PDF page 296. The fuse for the unregulated +15 volt supply going to the high voltage inverter is shown on the left side of schematic 8 which is PDF page 300." ======================================================== On ALL my PDF manuals of which I have 4, all the same 320 page PDF files, there are no schematics on pages 296 or 300, so I had to search for them by scrolling through many pages. With that said I found Q1195, THANKS David! I measured the voltage on the collector, it reads +22.3 volts, I know David said +15 volts unregulated So could that be normal as it is not regulated? I do have some very old 2N3055 power transistors but I would hate to pull out the HV board and have it blow. BTW I no longer have a transistor tester, years ago I had a Sencore Super Cricket but that got sold dirt cheap. From what David said fuse F814 supply's the unregulated +15 volts to Q1195, but like I mentioned in this posting PDF Page 300 does not show a schematic, in fact there are NO schematic numbers shown in these PDF manuals I have but it does show what circuit they are. This is one big reason I am having such a bad time with these PDF's THANKS guys" David, if you have time what do you think? Thank you for helping solve this problem!!! |
| David Hess:
--- Quote from: finom1 on May 03, 2017, 09:14:52 pm ---I measured the voltage on the collector, it reads +22.3 volts, I know David said +15 volts unregulated So could that be normal as it is not regulated? --- End quote --- That is the normal voltage. The +15 volt unregulated supply is used to feed the +15 volt regulator and it also feeds the high voltage inverter. Its minimum voltage has to be higher than the dropout voltage of the +15 volt regulator so +22.3 volts is about right. --- Quote ---From what David said fuse F814 supply's the unregulated +15 volts to Q1195, but like I mentioned in this posting PDF Page 300 does not show a schematic, in fact there are NO schematic numbers shown in these PDF manuals I have but it does show what circuit they are. --- End quote --- Our PDF files might have a different number of pages. The schematic numbers are marked in a lower corner with the schematic number. Artek Manuals has a complete scan of the 7633 manual and they includes indexes making it easy to find specific pages for about $7. Their quality is usually pretty good. http://artekmanuals.com/manuals/tektronix-manuals/ --- Quote ---David, if you have time what do you think? --- End quote --- If the inverter is operating, then there should be a high level of AC at the collector of the transistor so look for that using an AC voltmeter or another oscilloscope. I think the only way the inverter could not be oscillating *and* fuse F814 not be blown is if Q1195 was open or if the transformer bias winding to the base of Q1195 was open. If Q1195 and the transformer was good, then the high voltage regulator circuit would drive Q1195 hard blowing fuse F814 and that did not happen. So the likely problem is Q1195 being open. Unfortunately this leaves the question of why which is why I recommend gaining access to the high voltage board to test the transistors in the regulator circuit and measure the resistance of the transformer primary and bias winding. Before taking anything apart, check for an AC voltage on the collector of Q1195. It should be about 40kHz. |
| tautech:
A quick test to see if these inverters are working is to look for the EMI they produce when running. David has mentioned 40 KHz and this can be identified with another scope without connecting but just using a probe close by, ahla near field probe style. |
| finom1:
--- Quote from: David Hess on May 03, 2017, 09:38:01 pm --- --- Quote from: finom1 on May 03, 2017, 09:14:52 pm ---I measured the voltage on the collector, it reads +22.3 volts, I know David said +15 volts unregulated So could that be normal as it is not regulated? --- End quote --- That is the normal voltage. The +15 volt unregulated supply is used to feed the +15 volt regulator and it also feeds the high voltage inverter. Its minimum voltage has to be higher than the dropout voltage of the +15 volt regulator so +22.3 volts is about right. --- Quote ---From what David said fuse F814 supply's the unregulated +15 volts to Q1195, but like I mentioned in this posting PDF Page 300 does not show a schematic, in fact there are NO schematic numbers shown in these PDF manuals I have but it does show what circuit they are. --- End quote --- Our PDF files might have a different number of pages. The schematic numbers are marked in a lower corner with the schematic number. Artek Manuals has a complete scan of the 7633 manual and they includes indexes making it easy to find specific pages for about $7. Their quality is usually pretty good. http://artekmanuals.com/manuals/tektronix-manuals/ --- Quote ---David, if you have time what do you think? --- End quote --- If the inverter is operating, then there should be a high level of AC at the collector of the transistor so look for that using an AC voltmeter or another oscilloscope. I think the only way the inverter could not be oscillating *and* fuse F814 not be blown is if Q1195 was open or if the transformer bias winding to the base of Q1195 was open. If Q1195 and the transformer was good, then the high voltage regulator circuit would drive Q1195 hard blowing fuse F814 and that did not happen. So the likely problem is Q1195 being open. Unfortunately this leaves the question of why which is why I recommend gaining access to the high voltage board to test the transistors in the regulator circuit and measure the resistance of the transformer primary and bias winding. Before taking anything apart, check for an AC voltage on the collector of Q1195. It should be about 40kHz. --- End quote --- David, thank you for all the details!!! |
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