[TechAssist] RCA MM52100 (MMC102 chassis) dead

From: "Gemini Computer & TV" <geminitv@xxxxxxxxxxxxxxxx>
To: "Techassist" <techassist@xxxxxxxxxxxxx>
Date: Tue, 10 Jun 2003 15:04:41 -0400
Okay folks, looks like I got me a good one so I need the collective minds of
the best and brightest out there. This set is dead and cycles three or four
times. You initially hear the high voltage for an instant before it shuts
down any cycles. I did several tests to isolate the shutdown as per the
Thomson servicing procedures, training manuals, and troubleshooting
flowcharts without success so I called Thomson Technical Assistance and
after extensive troubleshooting time forcing the set on, we both confimed
the high voltage, power supply, and horizontal deflection, vertical
deflection, and scan loss circuits are operating normally. We found that the
problem appears to be caused by faulty clock and data lines, specifically on
the output from the deflection SIP PCB (pins 12 and 14 are the clock and
data lines respectively). I was reading about 1.8 volts DC and 3.4 volts DC.
If I lifted those pins on J14102, I was back at 5 volts on both. We then
surmised that the SIP board was causing the load, so I ordered one from
Jason at Excel Distributing and put it in late last night with no change.
Thomson assisted me again this morning and we tried to clear the registers
and defeat scan loss detect so we could take some dead set readings with
Chipper Check for error codes. That endeavor was not successful as it was
unable to communicate with the set. We found that the Run1_I2C_CLK and
Run1_I2C_DAT lines on pins 1 and 12 of the multiplexer IC (U13203) were
reading very low DC voltage, about 0.673 volts on both when we should have
been reading about 4.6 volts. I then remove surface mount resistors R16544,
R16545, R22307, and R22308 to open the paths. I do have the 5 volt standby
at source +5VsFAIO and read it across all the pullup resistors into U13203
except R13276 and R13277 which are the clock and data lines I am having the
trouble with. I then removed U13203 to see if that was loading the lines
down but again it was still the same. That only left one path for these
specific lines and that was over to the I2C bus transceiver portion of the
F-PIP IC (ref# U18100) on pins 26, 27, and 28 via Q18102, Q18103, and Q18104
which I also opened but again I still have the same readings. These
components are all on the I/O board which is double soldered and double
sided and is a real joy to access and troubleshoot to which those of you who
have had the fortune to work on will testify to. So at this point, I am
rapidly running out of ideas and welcome yours. This is the toughest dog I
have encountered in quite some time!

Bob Waterman, CET® #RI-28
Master Technician License #9109
Service Manager / Parts Manager
Gemini Computer, TV, & Security Alarms
(508)695-7302
(508)695-7769 FAX
geminitv@xxxxxxxxxxxxxxxx
geminitv@xxxxxxx
www.geminicomputertvsecurityalarms.com

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[TechAssist] RCA MM52100 (MMC102 chassis) dead

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