The t922 is basicaly the same, so check
for info
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On Tue, Sep 1, 2009 at 6:55 PM, sst00940<b_willemaers@...> wrote:
Hello.
I've got a problem with a T935a scope. The indicator led on the front panel
flashes, which indicates a faulty HV power supply. Thus nothing is
displayed.
As a disclaimer, I must say that I've worked with DC voltages above 300V
before (for hifi tubes amplifiers) but that I've no experience with such
switching power supply. Sadly, this was also my only scope. The only other
tool I've got is a DMM.
- The slow blow 60ma HV fuse has blown. Replacing it doesn't fix the issue.
Powering the unit for at most a pair of seconds revealed excessive current
draw (320ma through r458!) so I quickly shut the scope down.
- Powering the scope in serie with a 20W lightbulb gives me the following
readings:
- The low voltage supplies are fine (tested by powering the scope with the
HV fuse removed).
- When feeding 8V @15khz into the primary of the HV transformer (through
r458), I get the following readings:
6.5VAC developped accros r458.
2.5VAC developped accross the primary.
81VAC appeared on pin 9.
26VAC appeared on pin 10 and 8.
nothing appeared from pin 3 to 6.
- the winding in between pins 3 and 6 is a short for my DMM.
It has been suggested to me that the feedback winding might be shorted. I
would really appreciate if anyone could confirm this diagnosis or suggest
another reason/fix for this failure. Finding a replacement transformer might
be near to impossible I'm afraid.
Thank you in advance for any help,
Ben.
