Re: Just got a 475, nothing showing on display


Alexandre Souza
 

Change ALL tantalum caps. Probably it will work =)

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Em ter., 28 de jul. de 2020 às 18:24, <jakenicholasward@...> escreveu:

Hey guys,

I just got a Tektronix 475 from ebay. The fan spins, lights come on, but
there’s no trace and no dot when I hit “beam finder”. I measured the power
supply test points and got these results:

+5: 4.99v, 48.5 ohm to ground, 0mv ripple voltage
-8: -7.96v, 40.8 ohm, 0mv ripple
+15: 14.98v, 68 ohm, 4mv ripple
+50: 50.00v, 2.78k ohm, 36v* ripple
+50 unregulated: 67v, OL, 31.9v* ripple
+105/160: 139.4v, OL, 13.8v* ripple
+110: 111.1v, OL, 20.9v* ripple

* where I measured high ripple voltages, my multimeter switched back and
forth from That voltage to zero in about 1 second intervals. Not sure what
that means.

The resistance on the +5, -8, and +15 volt rails seems very low, is that
normal? I didn’t see any expected values in the service manual (although I
haven’t read too deep).

I also noticed some kind of corrosion around where the giant caps(?) are.

It might be worth noting that the beam finder seemed to work on the ebay
listing, but I haven’t been able to make it work.

I’m new here and fairly new to electronics in general so I’d appreciate
any help. Thanks!



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