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Just got a 475, nothing showing on display: Tanatalum Caps


Jeff Kruth
 

In my experience, if a unit has a bad tant or two, it may pay to replace them all, esp if not the sealed hermetic type, since you are already in there. The orange (maybe blue, sometimes red) "Gumdrops" really suck. I have had several hundred (!) bad over the years, particularly in WJ & Racal synthesized radios & microwave sig gens.

73Jeff KruthWA3ZKR In a message dated 7/30/2020 11:29:34 AM Eastern Standard Time, cfharris@... writes: You are aware that the polarity marker on tantalum
capacitors is always the "+" terminal, right?

-Chuck Harris

David Kuhn wrote:

" Change ALL tantalum caps"

Tantalum?  Unless they are shorted and burned, why woiuld you change a
bunch of tantalums?  Granted they can put off a firework show when they
blow, but that's fairly rare.  I've had more brand news ones pop than old
ones (probable black bar marked on wrong end).

Dave

On Wed, Jul 29, 2020 at 2:48 AM Alexandre Souza <
alexandre.tabajara@...> wrote:

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!