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#1
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Good question, I guess my rule of thumb is bath water warm but no more than what your fingers can tolerate for say 10-15 seconds. Sorry I can't put a number to this but the HOT itself is known to run warmer than the transistor in these.
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#2
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New HOT, cleaned CRT pins & reflowed pads on CRT socket, and the TV is still doing the same shit (no lightbulb!). The picture starts normal but then gets too bright & loses H sync. At this stage +B is 131 to 132v. The colors get VERY saturated, and soon Green disappears followed by Red and Blue. Then all you've got is a bunch of monochrome garbage lines dancing across the screen. Sometimes, a bright colorful flash appears indicating something just disconnected. +B jumps to something like 139v in this state, and what once was a fluctuating whining noise becomes a monotonous high pitch. Orange filament glow disappears I think.
Next to the flyback, there is a pot labeled "SUB BRIGHT". Should I bother? Edit: Just did another test run. The picture lasted for a few seconds but then the magical flash appeared and +B dropped to 127v! Last edited by luRaichu; 04-22-2024 at 06:05 PM. |
#3
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Perhaps the screen grid (G2) are cranked up. Is interesting to reduce it to see that happens. ***if is the oscillator protecting something or faulty oscillator.
__________________
So many projects, so little time... |
#4
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Those big resistors just to the north of the B+ adjustment. Seriously if it was mine I'd go over every solder connection on the board with a touch of solder and replace all of the supply capacitors, they're 40 years old now and not getting any better.
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#5
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It doesn't help that the nearly half-century old flux smells bad when heated. I already replaced all the electrolytic capacitors in the video circuit (sound circuit was left mostly untouched) - what exactly is a supply capacitor?
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Audiokarma |
#6
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The capacitors that are involved in the power supply itself, replacing the caps in the video circuit have nothing to do with the power supply itself. Those would be the likes of C558, C805, C502, C307, C203, C564, C1603 & 1604 for starters.
I know that flux smells bad, been burning that stuff since the late 70's myself so I know where you're coming from but when you described having to hit the set and things started working that was the first clue to intermittent connections. The gradual shift to bright then loss of H-sync points to either a thermal issue that might be taking down a power supply line or a bad capacitor that's hogging current. You found that bad one over in the horizontal and while the 80's didn't have the "capacitorgate" they're still prone to failure due to their wet internal construction. Just the nature of them. If the smell of the flux is that offensive it can be washed off using either acetone or isopropyl alcohol however the main board should be removed as these will damage the cabinet plastics. Learning electronics isn't easy, after 45 years I'm still learning and getting off the ground can be really tough when you're dealing with a tough dog. Test equipment is essential but sometimes the best tool is the experienced gained over the years, best advice I can offer is to take it slow, read & study the schematics and stick with it. I started swapping tubes in old B&W sets when I was in the 3rd grade when Carter was in office. You will get there, problems are only opportunities in work clothes that are designed to bring you up to the next level. You CAN do it. |
#7
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That's why I alluded to the Sub Bright pot. Perhaps we can see if running dimmer will stop the horizontal f*ckery. Then we will know if it's an undercurrent or overvoltage problem. I'm tempted to think it is overvoltage, like zeno said. Quote:
My last and first recap was a Macintosh LC. The logic board required surface mount caps while the rottening power supply used through-holes. |
#8
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I agree with the other post about the supply caps. Pull and test any electrolytics in the supply. That's 802 803 804 805 in the 130 V, 502 in the 12V, and all those other small voltages, C558 C203 C307 C564 C1603 C1604 Pay special attention to the caps shaded in grey If you don't have an LCR meter, you can buy one of these cheapo component testers off ebay or amazon (any of them are the same not just this link) It's not going to be super accurate, and it can't go up super high in capacitance, but it will at least give you a go-no-go reference for telling if a cap is super high ESR or open or shorted in some way Also you might want to test the supply transistors. Q801, Q802, Q552 You can either test each leg just to confirm they are functioning as transistors still, but those cheapo component testers will quickly tell you if they are probably still working or not as well Last edited by vol.2; 04-23-2024 at 10:38 AM. |
#9
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I replaced all of those except C1603 or C1604 since they were on the channel selector board. Best to do that while we're at it.
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#10
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I was attempting to test the 160v supply. I measured the positive leg of C559 to ground, it was something like 140v. But then the HOT popped again. I am so sick and tired of throwing away money at new HOTs.
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None were grey?! I suppose it doesn't hurt to try. |
Audiokarma |
#11
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Sorry, those caps shaded in grey in the Sam's. Grey means they are important, both in terms of failure and in terms of observing correct values when replacing
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#12
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#13
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My bad, I miscalculated the multimeter readout. It's actually 3550Ω, which is way short of it's original value of 12kΩ.
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#14
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Remove one leg and measure again, to be sure (if you don't tried to measure this manner). Possibly some other resistors are in current measuring path.
__________________
So many projects, so little time... |
#15
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I swear there's no control labeled contrast. These are all the easily accessed knobs,
On the front of the case: Bright Panabrite Tint Color ColorPilot (on/off) On the right side: Sharpness V-Hold On the neckboard: Screen Low Light Red Low Light Green Low Light Blue Red Drive Blue Drive |
Audiokarma |
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