[TechAssist] Re: [Fwd: update.Re: NEC P7701 Multisync 70 relay may chatter at turn on,no display.]

  • From: "Jerry" <geiting@xxxxxxxxxx>
  • To: <techassist@xxxxxxxxxxxxx>
  • Date: Fri, 16 Nov 2001 21:31:48 -0500

Sounds like you are on the right track.  The filament load current is higher
@ turn on than when it's warmed up, so the SMPS may be going into an
overcurrent shutdown mode.  Maybe bad cap or I have also seen the SMPS
output FET-to-ground resistor change value slightly, which trips the
overcurrent sense input on the controller ic.

Jerry
Christians Electronic Service

----- Original Message -----
From: "Phil Bader" <philbad@xxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Friday, November 16, 2001 5:39 PM
Subject: [TechAssist] [Fwd: update.Re: NEC P7701 Multisync 70 relay may
chatter at turn on,no display.]


|
|
|
| -------- Original Message --------
| Subject: update.Re: NEC P7701 Multisync 70 relay may chatter at turn
| on,no display.
| Date: Fri, 16 Nov 2001 17:16:44 -0500
| From: Phil Bader <philbad@xxxxxxxxxx>
| Organization: Jan Phyl TV Inc. Winter Haven, Fl.  Estab. 1976
| To: Electronic Hardware Repair <ELREPAIR-L@xxxxxxxxxxxxxxxxxxxx>
| References: <3BF19BB7.ADB2C584@xxxxxxxxxx>
|
| After much testing,Iunplugged CRT socket.Behold!Unit clicked once,HV
| came up and stayed.I replaced the rectifier and cap in this 6 volt line,
| D113, C122 (1000mfd). No help. I replugged CRT board back into CRT and
| unsoldered the actual CRT filiment pin (high side, +6V) and monitor will
| stay up and run.If, while it is on I jumper the fil pin, CRT will show
| good display.So, just unsoldering the CRT fil. pin does the trick.I
| ohmed the CRT fil. pins, no dead shorts,Fil volts no load at 8VDC, with
| load, 6VDC. I am stumped. It's like the CRT is loading this source and
| shutting down the SMPS. Ideas???
|
| Phil Bader wrote:
| >
| > Customer said it would "click,click,click".Sometimes it comes up with
| > good display here in shop. Other times, push power,hear relay clicking
| > erratically, or so rapidly,may almost vibrate.No HV, no display.-TIA,
| > Phil
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