Re: 2235 power supply noise


I'm completely at a loss as to how to proceed now. Is the problem elsewhere? Is my replacement
T906 faulty?
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:

2213A B016090
22I5A B013550
2235 B015626
2236 B014885

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

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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