Re: 2465B vertical shift problem

Chuck Harris
 

Don't condemn the vertical hybrid just yet. First,
check that you have all of the proper power supply
voltages at U119 on the motherboard (see manual).
Next, check for a bad connection to the pins coming
out of the side of the CRT for the vertical deflection
plates, both at the output of the amplifier, and at
the termination circuit board.

Be warned that shorting either deflection pin to the
CRT's mumetal shield will instantly destroy the hybrid.

Avoid bending the pins close to the glass seal. They
are very thin pieces of wire.

I have the hybrids if you find you really need one.

-Chuck Harris

ppppenguin wrote:

When I move channels 1 or 2 down the screen the trace is compressed at the bottom. As if the gain near the bottom the screen is about half that at the top. The effect is identical on both channels. Channels 3 and 4 are OK. Channel 2 output is OK. This looks horribly like U400 is in trouble and I've heard these hybrids are unobtanium.

I'd like to look at the differential outputs of U100 and U200 (and U300 for that matter, simply for comparison) where they feed into U400 in case there's a silly amount of common mode offset which might be causing the problem. But I can't see anywhere on the topside that I can probe. Getting at the underside looks tricky.

I've checked the power going to U100/U200. The +5V, +6.2V, -15V, -8V and -5V rails all seem to be within 2% of nominal.

I've looked at this article which isn't 100% relevant but illustrates an interesting fault and showing that U400 isn't always to blame: http://worldphaco.com/uploads/TEKTRONIX_2465B_OSCILLOSCOPE_MAIN_BOARD_INTER-TRACK_LEAKAGE..pdf

Your help, wisdom and advice would be very welcome. Even if it's only to say that U400 has definitely failed and the getting a replacement is well nigh impossible.

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