Moderators: Dave Moll, Steve Anderson
Steve Anderson wrote:OK Harry, no problem with either cluttering up the previous thread or starting this new one...
Those voltages are in the right 'ball-park', it depends on your actual wall outlet AC voltage and the load which will vary a bit. So they're nominal voltages, anything within 10% should be fine.
If you've already checked the inverter transformer and it appears OK, it's time to check the semis, Q401, Q402 and Q405. Should any be defective they should be easy to replace with an equivalent, I downloaded the datasheets for them yesterday, none of them are particularly special.
If they appear OK try lifting one end of R421 and see if you get anything across C404, it could be anything up to 2kV so be careful. Most multimeters won't handle 2kV so you'll have to knock up a simple resistive voltage divider, say 10M in series with 1M, measure across the 1M. Don't worry about the actual reading, all we want to know is - is the inverter inverting? Remember the output voltage will (should) be negative.
Steve A.
Steve Anderson wrote:Yes, I prefer a 'proper' grounding wire and not rely on the PCB support pillars for it. One place where I worked the brass board spacers/pillars were replaced with plastic ones 'cos the bean-counters (accountants) said they were cheaper. Yep, you guessed it, the whole production batch of 500 radar transceivers refused to work. It cost far more than the bean-counters saved, 1) to rectify the problem, 2) to update the service manuals with the additional grounding wires being shown.
If anyone here is an accountant, I apologise.
Harry, the missing parts look like they were missing as it left the factory, not removed later, but I could be wrong. Remember it did work once in the past without whatever those components might have been. Components being deleted as a production batch goes along is not uncommon, or it's a provision for an option or an extra. A different CRT phosphor may require slightly different bias voltages for example. Unless it's really obvious that these components are essential for the thing to operate I wouldn't fret about it.
It's not easy to see from the photos what parts are actually missing, can you identify them? Rxxx, Cxxx etc..
Steve A.
Steve Anderson wrote:OK, you're getting there... I have very limited time today, but once back in Bangkok I'll study this and add my thoughts...tomorrow...
Steve A.
Steve Anderson wrote:Harry, some voltage checks are in order, but first I suggest trying this...
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