Doing me head in. This set originally had a short buffer-IC and a blown Y-SUS.
Replaced the buffers complete and all the 88N30 Transistors and the 2SK28 summit or other, and the surface-mount one that burns the board.....
--These parts, although S/H were confirmed as good before fitting.
I have no floating 5V or 15V supplies and VSC is (when buffers connected) -99V instead of -145V, and '0' when buffers not connected....
Traced a 670 ohm leak on the 5V rail to ADUM1410, digital isolator, so pulled one from another (dead) board, that didnt show a 670 ohm leak. Its 4.5K now, as is yet another (dead) Y-SUS.
Swapped over the resonant controller switcher chip for the floating-supply, still no supplies. One of the three I have stays dead cold, both the other switching chips get pretty warm--Even changed the transformer--No dice.
There's supply Vs, (205V) to the trans and the switcher chip, and no apparent shorts on the floating supply outputs. It doesn't even give a pulse of voltage on any of the floating rails when first turned on.
Vs, Va and 15V from PSU are present and correct.
Is it a known fault --the switcher chip on these sets, Its a MR4710, 7 pin TO220....?
Also--There's a tiny green LED just by the floating-supply section--Its on.
Any ideas....?
Replaced the buffers complete and all the 88N30 Transistors and the 2SK28 summit or other, and the surface-mount one that burns the board.....
--These parts, although S/H were confirmed as good before fitting.
I have no floating 5V or 15V supplies and VSC is (when buffers connected) -99V instead of -145V, and '0' when buffers not connected....
Traced a 670 ohm leak on the 5V rail to ADUM1410, digital isolator, so pulled one from another (dead) board, that didnt show a 670 ohm leak. Its 4.5K now, as is yet another (dead) Y-SUS.
Swapped over the resonant controller switcher chip for the floating-supply, still no supplies. One of the three I have stays dead cold, both the other switching chips get pretty warm--Even changed the transformer--No dice.
There's supply Vs, (205V) to the trans and the switcher chip, and no apparent shorts on the floating supply outputs. It doesn't even give a pulse of voltage on any of the floating rails when first turned on.
Vs, Va and 15V from PSU are present and correct.
Is it a known fault --the switcher chip on these sets, Its a MR4710, 7 pin TO220....?
Also--There's a tiny green LED just by the floating-supply section--Its on.
Any ideas....?
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