Hi Russ,
Welcome...
The 24.5V you measure on the internal fuse is actually the unregulated side of the +15V power supply, suggestimg that this very power supply does have juice to work from.
Curiously, it's this +15V supply that powers the FAN circuit.
So, it seems this power supply is a good starting point to start checking.
A lot on the 465 relies on the +15V rail and there are a lot of small tantalum decoupling capacitors spread everywhere in this rail.
They are prone to get shorted, sometimes poorly shorted, when they will heat and become visibly burnt, but sometimes they will go dead shorted and then they don't heat and will trigger the current overload protection of the power supply.
A good way to tell is by measuring the voltage drop across the current sense resistor that makes the over current transistor to conduct and drop the output voltage.
It's usually a resistor of less than 1 Ohm (I don't have the manual of the 465 at hand right now) and it mustn't be dropping more than 0.5V.
Please let us know how were the readings of all the low voltage power supplies.
Regards,
Fabio
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On Tue, Jun 19, 2018 at 03:51 pm, <musicamex@...> wrote:
Hi, I am a music teacher in Mexico to help keep kids here. I also teach how
to repair and build musicians gear including tube amps. I recently acquired a
Tek 465 donated to the program. There is no screen display and despite the 2
fuses are good and the power switch on light does show power is getting to at
least part of the scope.
I am not in the same league as most on this site. The 465 makes an average
tube amp look like a lightbulb by comparison. I downloaded the 465 manual and
service manual but really would appreciate a little step by step
troubleshooting help. I always suspect electrolytic capacitors over 10 yrs
old and read that the tantalum caps are also unreliable. The boards look like
the New Mexico balloon fest in places, so, where to start? The fuse inside
the 465 tests 24.5 V on both sides of the fuse, but i couldnt find a diagram
with test point values. Also it doesn't appear that the filament in the CRT is
lit and the fan doesn't activate when the power switch is turned on like with
my TEK 468. The 465 looks like it wasn't abused and has an IBM sticker on it.
It looks like one of the filter caps was replaced as it has a blue plastic
cover unlike the adjacent aluminum can caps. I haven't disassembled or
unsoldered ANYTHING yet. I understand that the 465 is one of the holy grail
TEK scopes and i think it might outlast me if I can get it working again.
Would someone please walk me through getting the display to come on? The main
thing we currently use oscilloscopes for is to track a frequency generator
audio signal through a tube amp, looking for a distorted sine wave to help
isolate where the problem(s) are. So highly accurate calibration isn't
necessary if there is a good clean sine wave when connected to the wave gen.
Thank you in advance, Russ
Fabio Trevisan