Tech Bulletin TB98-02: Modification to Improve Reliability of Marquee Focus Module

Tech Bulletin TB98-02: Modification to Improve Reliability of Marquee Focus Module
page 1 of 4
Date: April 1998
File No. TB98-02
Technical Bulletin
Modification to Improve Reliability of Marquee Focus Module
This bulletin explains what modifications
are required to ensure reliable Focus Module operation.
Applies to Focus Module (FCM)
with printed circuit board #50-002034-02P used in
Marquee 8110, 8500, 8500LC, 9500LC series projectors
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manufactured between July 1 1997 and April 20 1998.
Also applies to service modules at issue 1 or 2.
●
Background
We have recently seen a higher than normal failure rate of the focus module used in
Marquee series projectors. As a result of an investigation of the modules that have been
returned we have found that the failures have been concentrated in projectors
manufactured between June and October of 1997, with many of the failures occurring
on projectors built in July 1997.
●
Symptoms
Red, Green or Blue focus adjustment does not work properly or the Low Voltage Power
Supply (LVPS) pulses on and off. Replacing the FCM alleviates the problem.
●
Cause
We have determined that this symptom is caused by a bad batch of components
(specifically U101, U201 and U301) that fail and can short the power supply’s ±15V
output when the cathode ray tubes (CRTs) experience an internal arc. This arcing is
also known as flash-over or internal high voltage discharge, an inherent characteristic of
CRTs. While arcs can occur throughout the life of the CRTs, they occur most frequently
on newer CRTs and are not necessarily audible.
●
Action
Our solution will add protection resistors to the module to prevent damage to these
components in the future. Check the sticker on the edge connector (P11) of the
replacement FCM for the issue level. If it is marked “Issue 1” or “Issue 2”, you must
perform the following modifications to the replacement FCM before installing it in a
projector.
Return the defective FCM to Electrohome.
page 2 of 4
Date: April 1998
File No. TB98-02
Technical Bulletin
NOTE: FCMs produced after April 21, 1998 will be corrected for this problem, including
service replacement modules as well those in new projectors. These modules will be
marked as Issue 3 and will have the modifications described below.
●
How to Correct
IF YOUR FCM HAS ALREADY FAILED:
1. Remove the failed FCM from the projector and return it to Electrohome. Do not
attempt to repair the module.
2. Replace it with an FCM Issue 3 or higher (see instructions below for upgrading to
Issue 3).
FOR FUNCTIONAL FCMs:
Note: This modification requires handling of electronic components and
should be performed by qualified service personnel only.
Please use proper Electrostatic Discharge (ESD) procedures. If you are
uncomfortable with performing the above modification, it can be done for
you at an authorized Electrohome service depot.
1. Check the sticker on the FCM edge connector (P11). If it is at “issue 1” or “issue 2”,
you must perform the following modifications before installing the replacement FCM
in a projector. Do not modify boards having a higher issue level.
2. On the solder side of the FCM, locate the trace which runs between U101 pin 12 and
TP104. Note that if TP104 is populated with a test point, it must be unsoldered and
removed. Cut the trace approximately 3mm from TP104. Be careful not to cut any
of the adjacent traces. See Figure 1.
3. On the solder side of the FCM, locate the trace which runs between U201 pin 12 and
TP204. Note that if TP204 is populated with a test point, it must be unsoldered and
removed. Cut the trace approximately 3mm from TP204. Be careful not to cut any
of the adjacent traces. See Figure 1.
4. On the solder side of the FCM, locate the trace which runs between U301 pin 12 and
TP304. Note that if TP304 is populated with a test point, it must be unsoldered and
removed. Cut the trace approximately 3mm from TP304. Be careful not to cut any
of the adjacent traces. See Figure 1.
page 3 of 4
Date: April 1998
File No. TB98-02
Technical Bulletin
5. On the component side of the board, locate U101. Solder one leg of a 10k resistor
(Electrohome part no. 80-110025-11P) to U101 pin 12, solder the other leg to
TP104. The body of the resistor should be positioned on top of U101. See Figure 2.
6. On the component side of the board, locate U201. Solder one leg of a 10k resistor
(Electrohome part no. 80-110025-11P) to U201 pin 12, solder the other leg to
TP204. The body of the resistor should be positioned on top of U201. See Figure 2.
7. On the component side of the board, locate U301. Solder one leg of a 10k resistor
(Electrohome part no. 80-110025-11P) to U301 pin 12, solder the other leg to
TP304. The body of the resistor should be positioned on top of U301. See Figure 2.
8. Use a digital multimeter to check your work. You should measure about 10kΩ
between TP104 and U104, etc. If you measure about 0 Ω, the trace has not been
cut properly.
● Determining If Your Projector Requires Modification By The Date Code
Stamped On The Outside Of The Box
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Projectors which are date stamped after April 21 1998 are factory modified to include
the above modifications and require no corrective action to be taken. A date code is
stamped in ink on the outside of the projector box near one of the serial number/bar
code labels. If two different date codes are stamped, the most recent one applies.
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The format of the date code is Year, Month, Day, Hour. For example, April 21 1998 is
8D21B, where 8 represents 1998, D represents April (A would be January, B would be
February etc.), 21 represents the day of the month and the B indicates the hour.
For preventative maintenance, we recommend performing the modifications for
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projectors date stamped between July 1 and April 20 1998.
page 4 of 4
Date: April 1998
File No. TB98-02
Technical Bulletin
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