X50 Laser question

**bigalinwv** · 06-22-2008, 11:28 AM

I have a friend (long distance away) that told me his plain 8500 (NOT X50 as I had titled it, sorry) is falsing on laser ALOT. I basically told him to send it in, but then I wondered if he could just turn off laser to stop the laser falsing? He had said he thought the whole laser detector was a joke anyway, saying he figured if it alerted, he was done for anyway.

Any body know?

**Super Dave** · 06-22-2008, 12:43 PM

If it were ME, I would send it in, yes laser detection most times is a ticket notifier, however I would hate to disconnect it for the 1 time out of 100 it may save me...

Could his car, cell phone, wiring, etc. be setting it off or something? I have heard of stories of each of these messing with detectors...

**MEM-TEK** · 06-22-2008, 07:23 PM

Hi bigalinwv,

First, rule out electrical noise from the specific car in which the 8500 is used in by trying the 8500 in another car. Ideally, test the 8500 with another power cord since, rarely, the power cord (Smartcord) itself could be the issue.

The constant laser falsing is most likely caused by slight gaps which have developed over time between the long metal shield which covers the laser circuitry. The laser circuitry consists of IR detector diodes plus several amplifier stages composed of transistors. Thus the laser circuitry in a RD is heavily amplified, and since all diodes and transistors are subject to interference by microwave radiation, any slight gaps in the grounded metal shield which covers the circuitry can result in lots of random laser falses due to the microwave radiation emitted by the local oscillator board within the radar horn, or from any received microwave radiation from other sources such as some cell phones, cell phone towers, microwave door openers, alarm systems, et cetera.

So, detailed below, is how to fix this problem which sometimes occurs on aging 8500 RDs and 8500 X50 RDs. Another forum member has executed the repairs described below, and reported that the repair method resolved his laser falsing issue. But first a couple of disclaimers...

THE FOLLOWING IS PROVIDED FOR INFORMATIONAL PURPOSES ONLY AND IS WITHOUT ANY WARRANTY, EITHER EXPRESSED OR IMPLIED, OF ANY KIND.

ALL ELECTRONICS ARE SUBJECT TO ELECTROSTATIC DISCHARGE (ESD) DAMAGE CAUSED BY STATIC ELECTRICITY. IF YOU ARE NOT FAMILIAR WITH HOW TO TAKE PROPER ESD PRECAUTIONS, DO NOT ATTEMPT TO OPEN AND/OR DISASSEMBLE THIS OR ANY OTHER ELECTRONIC DEVICE.

FINALLY, PLEASE READ VERY CAREFULLY AND FULLY UNDERSTAND THE FULL PROCEDURE AND THE REASONS FOR EACH STEP IN THE FOLLOWING PROCEDURE.

1. You will need some sort of anti-static work surface upon which to work on. A large aluminized mylar anti-static bag is ideal for this, and may be readily obtained from a local "mom and pop" computer store if you don't already have one. You will need to use scissors to cut open the anti-static bag since only the interior of the metallic looking aluminized mylar anti-static bag is coated with a very thin film of aluminum. The inside of the bag with the aluminum coating is what must be face up to serve as our anti-static work surface. Alternatively, you could use a large piece of aluminum foil as an anti-static work surface even though I prefer the anti-static bag.

2. Set the 8500 top-tide-down atop your anti-static work surface.

3. Remove the three screws on the bottom of the 8500 using a small Phillips head screwdriver.

4. Lift off the 8500's bottom cover, noting that you will have to pivot the cover in order to release the "snap" which is located on the side of the 8500 near the serial number sticker. Don't force the cover off. You should be able to quickly figure out how to tilt the cover in order to undo the "snap."

NOW THAT THE BOTTOM COVER IS OFF AND THE INTERNAL MAIN CIRCUIT BOARD IS EXPOSED, DO NOT TOUCH ANYTHING INSIDE UNLESS YOU KEEP EITHER A FINGER, A PART OF A HAND, A WRIST, OR PART OF AN ARM IN CONTACT WITH YOUR ANTI-STATIC WORK SURFACE ATOP OF WHICH IS RESTING THE 8500 RADAR DETECTOR.

LIKEWISE, DO NOT PICK UP THE INTERNAL ELECTRONICS OR SET DOWN THE INTERNAL ELECTRONICS UNLESS A PART OF YOUR BODY IS FIRST IN CONTACT WITH YOUR ANTI-STATIC WORK SURFACE.

5. Keeping some part of your body in contact with your anti-static work surface, flip over the 8500 onto the anti-static work surface and then lift off the top cover. Now you should see something like the following picture even though the following picture is a photo of the internals of an 8500 X50 which has the M4 horn.

In the above photo, I have drawn a yellow rectangle around the metal shroud which covers the 8500's laser detection circuitry. It is imperative that this shroud is pulled down tightly to the main circuit board without any gaps through which microwave radiation can get through.

6. Flip over the main circuit board assembly and focus your attention on the metal shroud "tabs" which pass through the circuit board and are bent over to secure the shroud to the circuit board. Here is a close-up photo of these tabs:

7. Now, the idea is with one hand to squeeze the metal shroud and circuit board together so that there is no gap between the circuit board and the shroud, and then to use the tip of a flat head screwdriver to press these tabs flat against the circuit board in the regions circled in orange, above, to assure that the shroud is pulled down tightly and in contact with the circuit board in these areas. In other words, the goal is that the metal shroud covering the laser circuitry on the opposite side of the circuit board must be pulled down tightly by the tabs by mashing the tabs as necessary fairly tightly against the circuit board.

AFTER PERFORMING STEP 7, ABOVE, YOU SHOULD REASSEMBLE THE 8500 AND CONFIRM THAT THE FREQUENT LASER FALSING IS GONE. IF NOT, THEN DO NOT PROCEED FURTHER SINCE, OBVIOUSLY, THE PROBLEM MUST BE SOME SORT OF OTHER PROBLEM.

8. Ideally, once the tabs are mashed fairly tightly against the circuit board and you have confirmed that the frequent and random laser falsing issue is resolved, you would want to use a Q-tip (cotton ear swab) or the tip of a fairly small jewelers screw driver to apply a tiny dab of solder paste at the center of the orange ellipses shown, and then to use a 15 or 20 Watt soldering iron to apply small amounts of solder to secure and bond the portions of the tabs very near where they pass through the holes in the circuit board. This method will assure a permanent removal of any gaps which have developed, due to slight flexing of the shroud and the main circuit board due to huge fluctuations in ambient temperature changes, between the metal shroud covering the laser amplifier circuitry and the main circuit board.

9. The metal shroud must be grounded to the underside of the circuit board where the tabs are located. Only one really good and solid solder contact is necessary to ground the metal shroud to the underside of the circuit board, but if you follow the procedure in step 8, then obviously you will end up with multiple secure and completely grounded contacts between the metal shroud and the underside of the circuit board where the tabs are located. Even if you don't do the procedure in step 8, then at least be sure to reflow, using a tiny dab of solder paste, one of the existing solder joints which assure contact between the shroud tabs and the bottom of the circuit board.

10. While you are at it, use a jewelers screwdriver and make sure that the screws which secure the metal radar horn assembly to the main circuit board are tight. A slightly loose radar horn assembly can cause Self Cal messages and false radar alerts.

11. Reassemble the RD in the reverse order in which it was disassembled.