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On 9/21/2020 7:04 AM, James wrote:
Thanks again Harvey.
I took the scope apart and pulled out the display module. Praise be, it's through hole components! It also appears that the HV section and horizontal deflection parts are all on this module.
Pretty much have to be.? The monitor is pretty much a standard VGA monitor (I'd think) and needs the usual assortment of HV section, Horizontal and Vertical drivers (for the yoke), and a video driver.
Following on I have a couple of further dumb questions:
The CRT has a white connector at the end, I presume it works like a valve base and I just gently pull it away from the CRT pins?
That would be right.? Make sure that you are pulling only on the socket, and not the pin holder/base of the tube as well.? I'd be tempted to try to very gently rock it back and forth in case the pins are somehow stuck.? It should be keyed, either by a keyway in the plastic base or, if like a 7 or 9 pin valve, pin spacing
Any advice/tips on doing this?
The service manual is full of obsolete part numbers for the electrolytics, with no datasheets easily obtainable. The caps are a mixture of 35-160V types from Nichicon and similar and all look fine but as yet unmeasured. It's probably easier to just pull them out and replace them, there's only a handful.
I'd? do a little probing of the power inputs with another scope (I think you said you had one) to look for that 30 KHz waveform. That might tell you which to replace.? Alternatively, you can (assuming it's a 15 volt line), tack a 100 to 1000 uf 25 volt capacitor across that at the input to the monitor and see what that does or doesn't do.
Another possibility is that if there's a shield around the HV (that's HT for you) transformer, then see if the screws are tight.
Do I need particular spec capacitors or am I likely to be ok if replacing 105C +50-20% types with others that meet this spec (and obviously the same or higher working voltage)?
The parts list distinguishes CAP;FXD;ALUM from CAP;FXD;ELECTLT. Are these all aluminium electrolytics or is there some other difference I am unaware of? They all look like electrolytics!
I suspect that they're all standard aluminum electrolytics, since this is mostly consumer level off-the-shelf electronics in the display.? I'd go for 105 degree C capacitors (typically you'd be getting 85 or 105, 105 lasts longer at higher temperatures, and even at lower ones), working voltage equal to or up to 50% more (that's arbitrary, but a slightly larger working voltage is better).? Do not use a 15 volt or 16 volt rated capacitor on a 15 volt line, just not enough headroom.
and for the actual value, most electrolytics are about -20% + 100% in tolerance, so putting a 150 uf capacitor in place of a 100 uf capacitor should be fine.? If you think it's part of a signal chain, as in a filter for a particular frequency, or something doing timing, then go for the same value.
Many thanks as ever in advance.
Not a problem.? Check out some of the other repair threads some time to see some general "what do I put in its place?" advice. Not sure if anyone ever collected this and put it somewhere.
Harvey
