C284 whistles in standby

[Genotrom]

I have a C284 that when it goes into standby starts to whistle consistently. As soon as it comes out of standby, the whistle is almost zero. It comes from some electronic board. I was just passing through, so I had little time for testing. Soon I will return to the place to try to identify the problem. Has anyone had this problem?

[occus]

Buzzing/Humming noise come from DCPU/FUPU (1/2)

<Symptom>
In a very quiet environment and a machine get into the ready status,
buzzing/humming noise may come from DCPU (power supply)
TABT1300108EN**
DC for C224/284/364/224e/284e/364e or FUPU (Fusing power supply) for C454/454e.

<Cause>
Operation noise of the Noise filter for fusing heater lamp mounted on the
DCPU/FUPU may hear in that environment.

< Field action>
Please adjust the Heater control level under the Service mode gradually
up to the level 4.

>The setting change is reflected
and works by turning OFF/ON Noise filter
the main switch.

[Bix]

<Cause>
Operation noise of the Noise filter for fusing heater lamp mounted on the
DCPU/FUPU may hear in that environment.

It's funny that a noise filter causes noise. is an oxymoron

[Genotrom]

Thank you occus! I have already tried this solution but without success. Is there any other advice? Or should I try a new DCPU/FUPU ?

[occus]

Is it the same sound? Have you ever heard the typical sound from the DCPU/FUPU?

In the past i had a 284e with a fax speaker that also made noises like this...


I've found a old tech info:
< Field action>
Please adjust the Heater control level under the Service mode gradually
up to the level 4.
>The setting change is reflected and works by turning OFF/ON the main switch.

If cannot be adjusted, please install the following firmware.
Only the Heater control level 4 has been changed so as to reduce the buzzing/humming noise more.

<Temporary Solution>
For C224/284/364/454
Please install the special firmware, ver. GC2-68 or later.
DL No.: C224/284/364: DLBT1202845EN** C454: DLBT1202847EN**

<Permanent Solution>
- For C224/284/364/454
The change will be applied on next released MR firmware.
- For C224e/284e/364e/454e
Please install the mass-production program, Ver.G20-63, or later.
DL No.:C224e/284e/364e: DLBT1311187EN** C454e: DLBT1311190EN**

<Subjected Machines>
C224/284/364/454/224e/284e/364e/454e