Tektronix 2230, identical to 2220, less a few switch options, working, voltage across R907 0.23Volts
JC
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--- In TekScopes@..., "Tan Chor Ming" <jonray03@...> wrote:
Hi Tom,
Thank you for the detail of the problem which is similar to my tek 2220.
I am still unable to nail down the problem. I believe the scope is working
normally, because when it fires up it works normally.
My feeling is that it poorly designed thermally for 230V operation
Do you have voltage measurement for tek 2235 on R907?
I am getting 0.198V (with the +5V to the storage board disconnected,
effectively turning off the storage function).
This means that without the storage function connection, the current on +43V
is slightly below 1A.
I am not sure if this is a normal condition but it should be similar to the
tek 2235.
Under this condition, the scope could operate for quite a while without
problem
Once the +5V is connected to the storage board, voltage at R907 goes up to
2.3V~2.5V or about 1.15 to 1.25A on +43 and the power supply will shut down.
Following done with little effect or improvement
- Change 3 filter caps (only those that are feels hot) - C960, C962, C964
(for -5V for 2220 only)
- Change NMOS P9070. When changing P9070, I used a separate heatsink for
P9070 and still such down happens which means it is unlikely to be caused by
the thermal shutdown board.
- Shutdown is more likely cause by spurious overload in R907
- Change C907
- Change CR907 (two diode in parallel)
- Added C919 with 1000pf in parallel. Lowered switching freq but still
having a heated P9070 which shuts down. Not sure what freq but it is
definitely audible.
Rgds,
Chor Ming
_____
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of tom jobe
Sent: Monday, January 23, 2012 11:17 PM
To: TekScopes@...
Subject: Re: [TekScopes] Re: Power supply problem with Tek 2220
