[Test-Equipment] Test-Equipment digest, Vol 1 #296 - Tek 475 HV Arcing...

Mon, 28 Apr 2003 06:04:18 -0700

Ross, ve6ars...

I fully agree with Rolynn Prechtl, K7DFW, who advised NOT readjusting the
HV.   Any change in the HV will change the CRT's sensitivity, both Vertical
and Horizontal, thereby affecting the calibration in BOTH V & H.
Decreasing the HV will cause the CRT to become MORE sensitive and will allow
the sweep and vertical amplitude to INCREASE...  Increasing the HV will
cause the CRT to become LESS sensitive and will allow the sweep and vertical
amplitude to DECREASE...  Connect a calibrated time-mark generator to the
scope and vary the HV... You'll see what we mean...

Perhaps a good cleaning will cure your arcing...  Be sure to thoroughly
finish your cleaning by wiping away any soap or detergent residue with
several CLEAN alcohol swabs... Don't allow any liquids to 'RUN'... keep
wiping with clean swabs until ALL traces of foreign matter have been
removed.  If you still experience arcing, a very light coating of 'CORONA
DOPE' will fix the problem.  Don't GLOB it on... Use just enough to stop the
arcing.  Also, check for coronal discharge by switching off the room
lights...  Switch off the 475, and wait until the power supply voltages are
completely discharged, ground the supplies, and the HV.  Then thoroughly
clean all areas that had coronal discharges, as mentioned earlier...

Never be afraid to try something new.
Remember, amateurs built the ark,
professionals built the Titanic...

vy 73 de Larry, W1GOR

> Message: 2
> Reply-To: "R. Dahl" <[email protected]>
> From: "R. Dahl" <[email protected]>
> To: <[email protected]>
> Date: Sun, 27 Apr 2003 09:49:49 -0600
> Subject: [Test-Equipment] Tek 475 HV Arcing
>
> I just obtained a 475 with option #7.
>
> It all seems to function properly except that the HV line to the crt is
> arcing to the chassis intermittently.  (at the connector where the black
> wire meets the red)  I have the service manual but havnt come across any
> reference to this specific problem.  Perhaps the HV is to high?
>
> In my 30+ plus years as a ham, I have tried to divorce myself from dealing
> with high voltages, but I guess I need to put one hand back in my pocket
> until I get this resolved.
>
> Any comments are most welcome.
>
> Ross
> ve6ars

> Message: 3
> From: [email protected]
> Date: Sun, 27 Apr 2003 14:26:28 EDT
> Subject: Re: [Test-Equipment] Tek 475 HV Arcing
> To: [email protected], [email protected]
>
>   Ross  - I have had this problem several times over the years, and have
> solved it with a good cleaning.
> There should also be a HV adj pot, which could be lowered if the
brightness
> is good.
>
> Will
> --__--__--
>
> Message: 4
> From: "Rolynn Prechtl   K7DFW" <[email protected]>
> To: <[email protected]>
> Subject: Re: [Test-Equipment] Tek 475 HV Arcing
> Date: Sun, 27 Apr 2003 11:38:02 -0700
>
>
>>>>> There should also be a HV adj pot, which could be lowered if the
>>>>>  brightness is good.

> Not! Changing the HV will cause the V and H calibration to be lost. The HV
> is specified, plus or minus a small percentage, and needs to be at that
> value.
>
> K7DFW    TEK Bvtn 66-71