giannibo wrote:
On 4 Gen, 15:48, Jim Yanik wrote:
Andreas Tekman wrote :





On 1 Jan., 17:09, giannibo wrote:
On 31 Dic 2007, 23:35, Jim Yanik wrote:
giannibo wrote
innews:dca6ef88-f731-49ca-9
:
On 29 Dic, 04:43, Jim Yanik wrote:
"DaveM" wrote
innews:gcOdnekazMCkC-janZ2dnUVZ_
:
"David Wright" wrote in message
...
If you get some money send it in for repair and calibration.
Co
st
on
good test equipment is out of site.
"giannibo" wrote in message

ups.
c
om
...
HELP! Someone know the mainframe oscilloscopeTektronix7000
series? I have some 7704 with power supply broken,with same
defect: don't start the oscillator.
Some suggestion??
You can download the manual for the 7704 from
http://bama.edebris.com/manuals/tek/7704/. It should help you
figure
out the problem.
The usual suspects are aging electrolytic capacitors.
both in the power supply and the mainframe itself.
just make sure you have a 7704 and not a 7704A. There's a big
difference.
although both have complex series-resonant switching power
supplies.
usually,you hear a clicking or "chirping" from the PS;it's
trying to start,but something is loading a supply,or a diode is
shorted. Some failures blow a lot of parts....and then the line
fuse afterwards.
--
Jim Yanik
jyanik
at
kua.net- Nascondi testo tra virgolette -
- Mostra testo tra virgolette -
Thanks for answer.The model is 7704A. I replace the fast
diode.The defect remaining is that try to start the
oscillator,but isn't stable.After several test, I found that
disconnecting the transisto
r
TO5 on parallel to base-emitter of power transistor, the
oscillator start, but isn't stabilized.May be is the small SCR. I
checked all components, only the SCR remain... Further the
semiconductor indicated
on circuit as a element with 2 emitter, what is?
A Diac;it triggers at ~33V IIRC.
This machine remain on
stock for several years, so some components are gone.Is a pity ,
because this instrument is made on beautifull mode, and I try to
save.
Thanking for help!!
Gianni
--
Jim Yanik
jyanik
at
kua.net- Nascondi testo tra virgolette -
- Mostra testo tra virgolette -
Thanks! I will replace it! In the meantime I foun that R120 and R122
( 1,8 Kohm) of Z axis board A41 are burning, with smoke. Many defect
all togheter!! Tomorrow i will check why these resistor are
smoking.Anyway I am bidding on ebay a 7704 so I can compare some
situations.
Thanks. I wil post when I found all defect!
Gianni
IK4EWH- Zitierten Text ausblenden -
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Remember what Jim already said about 7704 and 7704A: Both models are a
lot different.
So if you plan to compare circuits and repair faults, go for the same
models at least.
hth,
Andreas
7704A uses a TEK-made IC for it's PS control,while the older 7704 non-
A uses discrete circuitry.
The A model has more control loops.

--
Jim Yanik
jyanik
at
kua.net- Nascondi testo tra virgolette -

- Mostra testo tra virgolette -

Infact: all IC are custom, with various models.Now I am arrived to
have: trace very weak, but seem trigger and vertical work.There is a
problem: the trace is only present on central zone of tube. I never
seen a wiew like this. I fund another mainframe so I can replace step
by step the circuit, so I can see which one is defected.
But really this is on very bad conditions. I repaired a lot of
465-475-7704-7603 and others , but this is very hard!!

Depending on which version you have, there's a bleeder resistor on the
HV board...actually a bunch of 'em in series. They go open, the high
voltage goes up, the trace shrinks.

Mine had four of about 7 open resistors in series. I found that
improbable...
The explanation given was that they're carbon and they crack. Then
the first one arcs to keep the current flowing until the second one
cracks and opens...which arcs...until finally there are enough of them
open that it can't sustain all those series arcs at once and the string
starts acting like it's open.

--
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