Re: 2465 no traces, no OSD
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>Last night I found that VR2420 was shorted You are definitely on the right path.? The flashing LED and variations when you select a control points to the control board.? The DAC reference is a key factor in the control logic.? But it puzzles my why it would fail in such fashion.? I would look around for physical damage by a clumsy or unskilled technician.? No matter, you know what to do and it may be the major fault here.
From: tinkerer138
To: TekScopes@...
Sent: Thursday, January 30, 2014 8:15 AM
Subject: [TekScopes] Re: 2465 no traces, no OSD
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--- In TekScopes@..., machine guy wrote:
> >Thanks, this looks promising (not to mention fun:).
> Are we having fun yet??? lol.??
Hell yes!
> I wont be much help to you with the control board.
No worries, you've set me on the right path, and I think I may be able to sort out at least what I've discovered so far. I'd hope noone here minds if I keep a "diary" of what I find as I go along. I'm hoping this might help someone else later, as I've been helped by others lore and repair logs.
Last night I found that VR2420 was shorted, and was pulling the -1.25 reference to ground at ~10Ohm. This is a 3V zener that's presumably there to clamp the reference to +.7- -3V.
It looks like whatever took out the zener also burned U2420D (1/4 TL074), as when I removed the zener, the rail went to -5V, irrespective the drive on the input.
So, whatever happened there may have been a fairly violent event. I'm guessing downstream from the -1.25V rail from A5 I may find more trouble.
I'll have to buy some parts and replace the op-amp, see what happens next.
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