Thank you Hakan!
This kind of good information is very rare to see, and hopefully it will
help the current 2235 problem being worked on.
This information will help many folks in the future!
On 10/20/2017 6:30 AM, hahi@... [TekScopes] wrote:
I'm completely at a loss as to how to proceed now. Is the problemelsewhere? Is my replacement
Please help!This was a known problem at the time.
See these articles from the internal Service Info from 85 and 87:
RE: Mod #54681
Implemented in Manufacturing:
The preregulator and DC-DC converter
frequencies may be harmonically close
enough to produce an audible beat.
This anomaly will only occur after
changing some major power supply
frequency determining part, e.g. T944.
Engineering, changed R919 to a
selectable part, allowing a Technician
to alter the preregulator frequency a
small, but sufficient amount, thereby,
stopping the audible beat.
R919 Nominal value 10Kohm 315-0103-00
Alternate value #1 11Kohm 315-0113-00
Alternate value #2 9.1Kohm 315-0912-00
2213/2215A /2235/2236 AUDIBLE NOISE
FROM POWER SUPPLY
REF: Mod #61544
S/N: Not available
There have been three "speakers"
identified in the 2200 Series which
emit high-frequency audible sound from
the power supply. Due to the urgency
of this change to the field, only two
of these components have been changed
on this mod. These components and new
Tektronix part numbers are as follows:
T906: Tektronix P/N 120-1439-01
C907: Tektronix P/N 285-1177-01
In a very few instruments T948 was
found to be the third culprit. Changing
this part number will require UL
testing and recertification, so some
testing and evaluation need to be
conducted before the part can be modified.
If an instrument comes into the Service
Center with this problem try changing
C907 first. If this does not eliminate the
sound, change T905.
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