A colleague has asked me to look at an intermittent fault on
his BenQ video projector. This is the first projector I've
worked on, I'm more used to TV and VCR repair (and digital
asic design, my "day job").

There seem to be two (possibly related) problems, which both
its owner and I have witnessed:

1) Sometimes it shuts down during use. Lamp goes out.
The red LAMP error led comes on (and stays on), the power
led blinks green for 2 mins (the normal power down delay,
with fans running) then the fans stop and the power led
goes yellow (normal for standby). TEMP led stays off
LAMP led stays on.
If one then presses the power button the LAMP led goes
out and it powers up again normally.
It may work normally after this (for hours), or it may
shut down again after ten more minutes or so, and one
has to repeat the process.

2) The colours can get confused. The one occasion that it's
done this while I've had it, the colours just seemed to
go funny in the middle of a film. Generally looked like
a loss of saturation, and an odd purple hue. A slight
flicker of the image too, I think. I powered it down and
up again and all was normal again. I guess the colour
wheel got out of sync somehow?

It'll work fine for several days between failures.

The owner has had it from new, the lamp is original and has
only clocked up 236 hours (of 2000 hour quoted lamp life).
So I'm reluctant to think it's a real lamp problem - and a
new lamp is rather expensive to buy just to try.

I've taken it apart, checked easy things (PSU, electrolytic
cap ESRs, examined closely for bad joints, reseated
connectors etc) but found nothing. After putting it back
together, I though it might be fixed, but a week or so later
it was back to its old tricks. :-(

Anyone out there with more experience of DLP projectors?
I see several "user reviews" of this model on websites,
many complaining of similar unreliability (but all praising
it for good image quality when it works!) Is there a generic
issue with this model, or maybe a known fix to apply?
I notice several places where there have been EC's applied
to the boards (resistors, capacitors hung off at funny angles)
suggesting an early model or flakey design to me.

I trawled the web for service info, but found only one BenQ
manual (on eserviceinfo, a much earlier PB6100 model), and found
no sites offering any BenQ service manuals for sale. Are they
generally available at all?

Can one hook a PC up to it, and get an error log out of it
or otherwise put it into a "service mode"?

It uses a EUC 250 P/01 lamp ballast, with a small (5-pin?)
control cable. It would be helpful to know the pinout of
this, I imagine it has a lamp fault line on it. Anyone know?
It also says "9137 001 71805 MADE IN HOLLAND" on it, which
makes me wonder if Philips were involved in the ballast.
Any info here would be gratefully received, I could hang a
logic analyser on it if I knew what to look for.
One of the signals here has a 2K resistor soldered onto
it. An attempted fix for a ballast interface problem maybe?
The ballast is pretty complex - with two daughter boards
soldered into a main board - and whilst I'm quite willing to
reverse engineer things in general, I think this would be quite
a hard one as it's multilayer PCBs. So that's a last resort.

Thanks for your help.

Mike.

In article , Remove _ for valid address wrote:
A colleague has asked me to look at an intermittent fault on
his BenQ video projector. This is the first projector I've
worked on, I'm more used to TV and VCR repair (and digital
asic design, my "day job").

There seem to be two (possibly related) problems, which both
its owner and I have witnessed:

1) Sometimes it shuts down during use. Lamp goes out.
The red LAMP error led comes on (and stays on), the power
led blinks green for 2 mins (the normal power down delay,
with fans running) then the fans stop and the power led
goes yellow (normal for standby). TEMP led stays off
LAMP led stays on.

[... snipped...]

It uses a EUC 250 P/01 lamp ballast, with a small (5-pin?)
control cable. It would be helpful to know the pinout of
this, I imagine it has a lamp fault line on it. Anyone know?
It also says "9137 001 71805 MADE IN HOLLAND" on it, which
makes me wonder if Philips were involved in the ballast.

I've now traced out the ballast control interface. In case
someone finds it useful, here it is:

logic board cable ballast
............................. ............................
_____ . .
|4 W . . _______
U5 |----+-------270R----5---yellow---5---100R---|k c|-- "dim"
_____| | . . +--------|a_____e|--
3K Z . . | _______
| +--270R----4---orange---4---100R---|k c|-- "on"
gnd | . . | +-|a_____e|--
Y c . . | |
-------------b +5V---3----red-----3-+------+ opto
e . . couplers
+5V | . . _______
| gnd gnd---2---brown----2----------|e k|--
10K . . +----|c_____a|-- "good"
X | . . |
-------+----------------1---black----1-----+
. .
............................. ............................

The top opto-coupler (associated with cable pin 5) seems to be on when
"economy" mode is selected, which dims the lamp.

The middle opto-coupler (associated with cable pin 4) seems to be used
to power the lamp on.

The bottom opto-coupler (associated with cable pin 1) seems to be on
when the lamp is operating normally. I suspect it goes off to signal
lamp fault detected. It is driven from a Philips P87LPC769BD chip
on one of the ballast daughter boards, this appears to be an 8051
derivative microcontroller. Presumably it measures and controls
the UHP lamp's voltage/current/etc and uses some proprietary
algorithm to decide when it thinks the lamp is unhappy and report
this (as well as shutting the lamp down).

Hopefully my logic analyser will determine the sequence of events
when it next fails...

Mike.

Hello Mike!

I'm having the same problem. My Model is PB8253. Projector started,
then afer a couple minutes it goes off with the red lamp led flashing.
Just replaced the lamp, but the problem persists. Tried to remove all
connecting cables, except for the power, but still the same problem.
Anyone with similar problem or solution, please contact me at




Thanks!