[TechAssist] Re: JVC - VCR - HR-S4700U - P.S. Problems - Followup
- From: "J Silverman" <greentron@xxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Mon, 16 Jun 2003 14:20:59 -0400
Look at the display power circuit for almost any vcr. You have a floating
filament supply, AC or DC, DC in this case. Heaters measure 10 to 20 ohms. A
network of resistors, 50 or 100 ohms, and a zener diode, usually 7.5 volts,
and a resistor to the -28 volts is used to bias the filament to about -7
volts. I have seen the 50 ohm resistors blown and the zener shorted. Its
very rare but there could be a heater to cathode or anode short inside the
display.
Jerry Silverman
Greentron Inc
4 Newland Ave
Greenville SC 29609
864 232 3889
Fax 271 2080
mailto:greentron@xxxxxxx
----- Original Message -----
From: "David Lessard" <mrfixit@xxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Monday, June 16, 2003 12:43 PM
Subject: [TechAssist] Re: JVC - VCR - HR-S4700U - P.S. Problems - Followup
> Pin 2 on connector CN1 is where the problem lies. When this pin is
> unsoldered the VCR fully funcitons, except no display. I ohmed that line
and
> it reads +30Kohms, so why does this cause the switching PS to stop? I
loaded
> this pin down with a 100mA bulb and the PS doesn't shut off, everything
> still functioned. I'm lost for an explanation here, without a schematic
this
> is proving to be a pain in the ass-ets.
>
> David Lessard
> Alexandria Electronics
> Ontario-Canada
> mrfixit@xxxxxxxxxxx
>
> -----Original Message-----
> From: techassist-bounce@xxxxxxxxxxxxx
> [mailto:techassist-bounce@xxxxxxxxxxxxx]On Behalf Of J Silverman
> Sent: Friday, June 13, 2003 12:45 PM
> To: techassist@xxxxxxxxxxxxx
> Subject: [TechAssist] Re: JVC - VCR - HR-S4700U - P.S. Problems
>
>
> Just remembered that when I borrowed those JVC manuals I used to copy the
> power supply drawngs. CN1 goes to the display board. Pins 1 and 2 carry
> floating 7 volts for the filaments. Pin 3 carries -28 volts for the
display
> driver IC (and maybe a memory or tuning chip). Pin 4 is ground. Pin 5 is
the
> switched 5 volts. You may want to ohm the -28 volts to ground to see if
the
> display driver IC is loading that line down.
> Jerry Silverman
> Greentron Inc
> 4 Newland Ave
> Greenville SC 29609
> 864 232 3889
> Fax 271 2080
> mailto:greentron@xxxxxxx
> ----- Original Message -----
> From: "David Lessard" <mrfixit@xxxxxxxxxxx>
> To: <techassist@xxxxxxxxxxxxx>
> Sent: Thursday, June 12, 2003 9:21 PM
> Subject: [TechAssist] Re: JVC - VCR - HR-S4700U - P.S. Problems
>
>
> > Load, drum, capstan, all work. As I said in my previous post, this VCR
> > functions (but with no display) when connector CN1 is disconnected from
> > power supply board. What I need is information on this connector, where
> does
> > it go? It looks like over to RF modulator, but I'm not sure. What ever
> this
> > connector is feeding is the problem. Could someone with a schematic
please
> > confirm this. Thanks in advance.
> >
> > David Lessard
> > Alexandria Electronics
> > Ontario-Canada
> > mrfixit@xxxxxxxxxxxx
> >
> > -----Original Message-----
> > From: techassist-bounce@xxxxxxxxxxxxx
> > [mailto:techassist-bounce@xxxxxxxxxxxxx]On Behalf Of becyn
> > Sent: Thursday, June 12, 2003 1:39 PM
> > To: techassist@xxxxxxxxxxxxx
> > Subject: [TechAssist] Re: JVC - VCR - HR-S4700U - P.S. Problems
> >
> >
> > I highly suspect that a motor drive IC has gone south. Check load, drum,
> > capstan, in that order.
> >
> > Jim McVey
> > McVey Alltronix
> > 327 Broadway
> > Newburgh Ny 12550
> > ph: 845 561 8383
> > fx: 845 561 9017
> > Consumer electronics &
> > computer service.
> > Factory authorized for
> > over twenty brands.
> >
> > ----- Original Message -----
> > From: "David Lessard" <mrfixit@xxxxxxxxxxx>
> > To: <techassist@xxxxxxxxxxxxx>
> > Sent: Thursday, June 12, 2003 1:53 PM
> > Subject: [TechAssist] Re: JVC - VCR - HR-S4700U - P.S. Problems
> >
> >
> > > No C33 in this SMPS. I changed C16 and C19, same results. You can hear
> the
> > > SMPS chirp a couple of times, then it shuts down. What I really need
> here
> > is
> > > reference to connector CN1 on the SMPS. Which circuitry does it feed?
> This
> > > is where the loading problem is. When CN1 is disconnected the VCR
works
> > but
> > > without a display. Round two...
> > >
> > > David Lessard
> > > Alexanria Electronics
> > > Ontario-Canada
> > > mrfixit@xxxxxxxxxxx
> > >
> > > -----Original Message-----
> > > From: techassist-bounce@xxxxxxxxxxxxx
> > > [mailto:techassist-bounce@xxxxxxxxxxxxx]On Behalf Of J Silverman
> > > Sent: Thursday, June 12, 2003 11:30 AM
> > > To: techassist@xxxxxxxxxxxxx
> > > Subject: [TechAssist] Re: JVC - VCR - HR-S4700U - P.S. Problems
> > >
> > >
> > > Is there a C33 in the power supply on that model?
> > > Jerry Silverman
> > > Greentron Inc
> > > 4 Newland Ave
> > > Greenville SC 29609
> > > 864 232 3889
> > > Fax 271 2080
> > > mailto:greentron@xxxxxxx
> > > ----- Original Message -----
> > > From: "David Lessard" <mrfixit@xxxxxxxxxxx>
> > > To: <techassist@xxxxxxxxxxxxx>
> > > Sent: Wednesday, June 11, 2003 6:02 PM
> > > Subject: [TechAssist] JVC - VCR - HR-S4700U - P.S. Problems
> > >
> > >
> > > > VCR came in dead, found information referring to C16 & C19, they
both
> > > > checked good and weren't replaced. I can get the VCR to come alive
> > (load,
> > > > play, ff, rr, etc.) but with no display when connector CN1 on the
SMPS
> > > board
> > > > is disconnected. My question is, what circuit does CN1 supply? I
> didn't
> > > have
> > > > the time to check if the CABLE in via the RF modulator was working.
> The
> > > > above results were via RCA A/V jack to a monitor. A partial scan of
> the
> > > > circuit supplied by CN1 would be very helpful. Thanks techs.
> > > >
> > > > David Lessard
> > > > Alexandria Electronics
> > > > Ontario-Canada
> > > > mrfixit@xxxxxxxxxxx
> > > >
> > > >
> > >
> >
>
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