Re: Power supply problem with Tek 2220
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Tan: ? ? ? ? I beg your pardon, I did not realize that you definitely do have the basic skills! ?But do buy or build an ESR meter, as a great number of ?problems are caused by defective electrolytics and they are very easily checked in circuit with the ESR meter. It just takes a few minutes to rule out this very common failure and then you can continue with further circuit diagnosis/analysis as required. But believe me, caps are a BIG problem and your "technician life" ?will go a lot smoother with an ESR meter--it sure has for me (I've been using one for almost 30 years and I still remember how it was before I got one)!! ?I read some time ago that about around 90-95% of electrolytics fail due to high ESR. Don't know if this is a legitimate figure but it
speaks for itself. Good luck. ? ? ? ? Terry
From: Tan Chor Ming
To: TekScopes@...
Sent: Friday, January 20, 2012 11:01 PM
Subject: RE: [TekScopes] Power supply problem with Tek 2220
?
Thanks Gary ,
Do you suspect that it¡¯s a cap ESR issue?
Why would it cause such a behaviour?
I believe you can infer a lot from the
behaviour than blind guesses that¡¯s where I am trying to tap from the
experienced engineers.
?
I suppose I have more than the basic
knowledge because I am an electronics engineer with working knowledge in vacuum
and solid state electronics.
I have built a scope from scratch, otherwise
I would not attempt so work with EHT.
?
Rgds,
Chor Ming
From: TekScopes@... [mailto: TekScopes@... ] On Behalf Of Terry Gray
Sent: Saturday, January 21, 2012
1:11 AM
To: TekScopes@...
Subject: Re: [TekScopes] Power
supply problem with Tek 2220
?
?
At least
check the incircuit power supply electrolytic capacitors for ESR. If you don't
have an ESR tester, buy one or build one. There is lots of ESR information on
the web and also in the archives of this yahoo group. ?You definitely need
one if you're considering working on this type of electronic equipment and
problems. Otherwise give the problem to someone else who has this essential
test equipment and basic electronic knowledge to assist in diagnosing your
problem. You are over your head without basic skills and test equipment.
?
From: Tan Chor Ming
To: TekScopes@...
Sent: Friday, January 20, 2012
8:45 AM
Subject: Re: [TekScopes] Power
supply problem with Tek 2220
?
?
Has
anyone seen this behaviour repairing Tek2000 series scope power supply?
1. When
power on from cold, it will fire up properly and stay on for a few minutes
2.?
Once it warms up, the power supply shut down and try to on again and it
continues in this on/off mode
3.?
Pre-regulator out = 43V? (between TP940 and TP950)
4.?
All voltages when the unit is stable for a few minutes are +8.6, -8.6, +5.2,
+100 are all ok.
What
are likely problems before I start ripping the components from the circuit?
?ttesenq@... suggested that
it could be the pre-regulator MOSFET P9070.
I
though that it could be a electrolytic cap but it doe not look likely because
electrolytic failure would not have allowed the unit to fire up for a few
minutes
It is
more likely a active component that weaken with increase temperature, so ttesenq@... could be
right.?
This
would mean Q947 and Q946 are also likely components
Any
other possible lead of similar experience.
?
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