[TechAssist] Re: Sharp 27" TV - CN27S18 - Turn ON then OFF - Followup - FIXED
- From: "David Lessard" <mr_fixit@xxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Wed, 23 Jun 2004 16:20:36 +0100
FIXED:
D713 (bad parts)!!! The first zener I installed became very leaky after
several hours of debugging, the second one got worse by the minute.
Alas, the zeners marked "NTE147" were not what they were marked as. To
confirm this I hooked up the last good zener in the bag to my bench
supply and monitored the voltage as I increased the supply voltage. Well
low and behold; a stable 5 volts all the way up to 24 volts (supply
voltage), it was no doubt a 5 volt zener. I installed a "used" 33 volt
zener off a junk board and everything was normal, 33 volts at pin 4. So
I soldered STRF6626 back in place and the TV fired up perfectly. So what
did I learn wasting all this time, never assume the new part is what
it's supposed to be, also never second guess your troubleshooting
skills. I may bench test all my zeners before installing them in the
future...but probably not.
David Lessard
Alexandria Electronics
Alexandria, Ontario
Mr_fixit@xxxxxxxxxxxx
-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of David Lessard
Sent: Tuesday, June 22, 2004 4:38 PM
To: techassist@xxxxxxxxxxxxx
Subject: [TechAssist] Re: Sharp 27" TV - CN27S18 - Turn ON then OFF -
Followup
MORE INFORMATON: (and loosing hair)
OK, this is my last post until I figure out more about how this
switching regulator circuit works. The startup voltage across zener D713
remains at 5.0VDC until the micro shuts off the relay (about two seconds
after it doesn't detect +B). For troubleshooting purpose I have the
relay jumped "ON". According to the STRF6626 specs the voltage across
pins 4 & 5 should reach 16 volts (typical) until the oscillator,
regulator, etc., starts then this voltage should reach about 18 volts.
So, the question now is what is causing the voltage to be so low? I'm
totally lost and I'm losing hair trying to figure out something that
should be so obvious (or not).
David Lessard
Alexandria, Ontario
-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of David Lessard
Sent: Tuesday, June 22, 2004 3:50 PM
To: techassist@xxxxxxxxxxxxx
Subject: [TechAssist] Re: Sharp 27" TV - CN27S18 - Turn ON then OFF -
Followup
SECOND FOLLOWUP:
OK, upon reviewing the STRF6626 specs closer I found that initially the
startup supply voltage is derived via R715 (off the AC) and C709, after
a successful oscillator start, the supply voltage is derived via R710,
D706 and R709. What would cause this regulator not to start; again I am
not familiar with this type of switching regulator circuit at all and
would appreciate any help.
Thanks again,
David Lessard
mr_fixit@xxxxxxxxxxxx
Alexandria, Ontario
-----Original Message-----
From: David Lessard [mailto:mr_fixit@xxxxxxxxxxxx]
Sent: Tuesday, June 22, 2004 2:17 PM
To: 'Gemini Computer & TV'
Subject: RE: [TechAssist] Re: Sharp 27" TV - CN27S18 - Turn ON then OFF
- Followup
FOLLOW-UP:
Replaced shorted zener D713 with 33 volt zener, should be a 32 volt
device however STRF6626 specs specify a maximum supply voltage of 35
volts, should be OK here. Also, replaced STRF6626 as it checked bad too.
NOW I still don't have a 18.5V supply at pin4 of STRF6626, therefore
STRF6626 is not working. Question: Where does this supply voltage
originate? I have a schematic and can't seem to find out where this
voltage originates from. I'd appreciate any help as I am not familiar
with chassis at all.
Thank-you in advance,
David Lessard
mr_fixit@xxxxxxxxxxxx
Alexandria, Ontario
-----Original Message-----
From: Gemini Computer & TV [mailto:geminitv@xxxxxxxxxxx]
Sent: Monday, June 21, 2004 1:35 PM
To: mr_fixit@xxxxxxxxxxxx
Subject: Re: [TechAssist] Re: Sharp 27" TV - CN27S18 - Turn ON then OFF
David,
I do not have this exact manual (Canadian model I believe) but I do have
the
27NS100 which has that same power supply configuration. D713 is indeed a
high failure item and is a 32 volt zener diode, Sharp part#
RH-EX0673GEZZ.
D713 should be loacted between pins 4 and 5 of IC701 (pin 5 is ground
and
you should have 1bout 18.5 volts on pin 4 of IC701). I will privately
email
you a PDF portion of that power supply area. I would also replace IC701
when
you replace this diode. Here is the PDF:
Bob Waterman, CETR #RI-28
Master Technician License #9109
Service Manager / Parts Manager
Gemini Computer, TV, & Security Alarms
(508)695-7302
(508)695-7769 FAX
geminitv@xxxxxxxxxxx
geminitv@xxxxxxx
www.geminicomputertvsecurityalarms.com
----- Original Message -----
From: "David Lessard" <mr_fixit@xxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Sunday, June 20, 2004 9:19 AM
Subject: [TechAssist] Re: Sharp 27" TV - CN27S18 - Turn ON then OFF
> I need the value of D713 near STRF6626 regulator. I believe it's 30V
but
> I'm not sure. This zener is shorted. Could it be the cause of the
> problem described below? Does anyone have a print for this model?
>
> Thanks,
>
> David Lessard
> mr_fixit@xxxxxxxxxxxx
>
> -----Original Message-----
> From: techassist-bounce@xxxxxxxxxxxxx
> [mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of David Lessard
> Sent: Friday, June 18, 2004 2:09 PM
> To: techassist@xxxxxxxxxxxxx
> Subject: [TechAssist] Re: Sharp 27" TV - CN27S18 - Turn ON then OFF
>
> I should elaborate on this problem. There seems to be no +B from the
> switching regulator. I do hear the relay activate and I can trace AC
to
> the regulator circuitry but that's it. Standby voltages are obviously
> working because the micro is responding to panel buttons and the
remote
> causing the relay to activate. I imagine the micro is also monitoring
> the +B or some secondary FBT voltage, if it's not present the micro
> turns off the relay. Question is, does the SMPS in this chassis fire
up
> when the relay activates or is it always on like in the RCA chassis's?
> Are those STR=F6626 regulators a common failure?
>
> Thanks again,
>
> David Lessard
> mr_fixit@xxxxxxxxxxxx
>
> -----Original Message-----
> From: techassist-bounce@xxxxxxxxxxxxx
> [mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of David Lessard
> Sent: Friday, June 18, 2004 1:25 PM
> To: techassist@xxxxxxxxxxxxx
> Subject: [TechAssist] Sharp 27" TV - CN27S18 - Turn ON then OFF
>
> When I press the "ON" button I hear the relay "click" ON then two
> seconds later it "clicks" OFF. Protection? What are the common (if
any)
> causes for this problem? HOT is good, standby voltage is good, what
else
> should I look at? No schematic here.
>
>
> Thanks in advance.
>
>
>
> David Lessard
>
> Alexandria Electronics
>
> 50 Harrison Street
>
> P.O. Box 1366
>
> Alexandria, Ontario.
>
> Canada
>
> K0C-1A0
>
> mr_fixit@xxxxxxxxxxxx
>
>
>
>
>
>
>
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