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Bill Petrowsky
First of all sensitivity was checked and noted on a specific frequency in each of the VHF, UHF, and 800 MHz bands. Then squelch was set to threshold on each stock, unmodified, scanner and signal strength required to open the squelch was noted for each frequency. The squelch was then set to tight on each scanner and again the required signal strength to open the squelch was noted for each frequency on both scanners.
The PRO-92A was then opened up and after trying a number of resistor values, it was found that a 3.3 K ohm (1/4 watt for tiny size) soldered across the outside terminals of the squelch control yielded a similar squelch action as the PRO-92. The terminals of the squelch control are very easily accessible on the bottom side of the circuit board the control is mounted to.
The 3.3 K ohm resistor across the 10 K ohm squelch control reduces the squelch range and effectively removes the critical precise threshold squelch setting. Tests and modification were done in a professional communications shop using an IFR1200 as the signal source. This modification should only be performed by qualified personnel.
The results are as follows:
PRO-92 Sens. Threshold Tight 119.100 (AM) .3 µV .3 µV 2.0 µV 139.260 (FM) .22 µV .2 µV 1.5 µV 155.670 (FM) .3 µV .3 µV 1.7 µV 454.0375 (FM) .25 µV .25 µV 1.6 µV 853.9875 (FM) .5 µV .5 µV 3.0 µV 866.0500 (FM) .5 µV .5 µV 3.0 µV PRO-92A 119.100 (AM) .3 µV .3 µV 10.0 µV 139.260 (FM) .3 µV .3 µV 4.0 µV 155.670 (FM) .35 µV .4 µV 6.0 µV 454.0375 (FM) .3 µV .4 µV 5.0 µV 853.9875 (FM) .6 µV .6 µV 8.0 µV 866.0500 (FM) .5 µV .7 µV 8.0 µV PRO-92A w/Modified Squelch 119.100 (AM) .3 µV .3 µV 2.0 µV 139.260 (FM) .3 µV .3 µV 1.6 µV 155.670 (FM) .35 µV .4 µV 2.0 µV 454.0375 (FM) .3 µV .4 µV 2.0 µV 853.9875 (FM) .6 µV .6 µV 3.0 µV 866.0500 (FM) .5 µV .7 µV 3.5 µVThe squelch control is mounted and soldered through the circuit board. The 3 terminals of the squelch control stick through the circuit board and very easily accessed on the back or solder side of the board. By observing the location of the squelch control itself, you will easily see where the control is mounted
The resistor is soldered across the 2 outside terminals of the control on the solder side of the board. The center terminal of the squelch control is left untouched. Care must be used in taking the scanner apart.
After removing the batteries and rear cover screws, the cover pulls off easily. The board to be modified is the one closest to the scanner front containing the speaker, display, and logic board. The front containing the speaker, display, and logic board is plugged into the rest of the unit by multi-pin connectors.
Gently prying on both sides between the front speaker board and the bottom chassis board will separate the main chassis from the front. The resistor is soldered across the squelch control terminals on the solder side of the bottom board, of the main chassis, or the side of the BOARD THAT FACES THE FRONT of the scanner. The location of the resistor is ample and easy for qualified personnel.
I strongly caution against attempting this with no experience as the scanner can easily suffer damage by a slip of the soldering iron. As internal tampering will void the scanner warranty, one may wish to wait until the warranty period is over. Also, this mod can also be very easily removed if desired to do so.
This modification will only effect the way the squelch action behaves, and does not affect the overall sensitivity of the unit. With the squelch not being razor sharp critical will allow the proper point for trunking to be set much more easily with little chance of going to far and losing the control channel which in turn causes loss of trunking. This will also help reduce squelch choppiness on weak signals in conventional scanning. Basically this mod takes the useable range of the squelch control and widens it out making it much more practical.
Jim Hoitsma
VE6JAH
As promised here are some pics of my 780 mobile setup in operation. I finally got it in my car yesterday.
It works very well but I honestly wouldn't recommend this to anyone without very good soldering skills or they may likely wreck their 780 in the process.
There are 31 soldered connections on each of the 2 parts. I had to remove the flat-flex cable connectors on the main board and solder onto the board directly (all surface mount of course) then connected to the DB37 connector. The display required 31 wires to be soldered from various points on the board to the DB37, including the 2 main knobs (12 wires).
The metal box for the back of the display was made (aluminum which was bent and then painted) as well as a covering for the opening of the main unit. The main unit is under the dash - with power, external antenna and external speaker (cord visible in pics) connected. The connection between the 2 pieces is ribbon cable (2.5 ft) with DB37 male/female connectors on either end.
I also have a program I wrote in VB that I use to program the 780 (for EDACS and conventional freqs) so the mobile setup won't be a problem. I don't monitor any Motorola trunking but may add it to the program someday.
Head and body, photo #1
Head and body, photo #2
Installed
Kevin Fisher
VE6OXR
As with any electronics work, please do not perform this modification unless you are qualified and competent to do so. I cannot be held responsible if you should damage your radio.
Disconnect the scanner from its power supply. Turn the scanner upside-down and remove the four screws from the bottom cover. There are two on each side. Gently lift the cover off a few inches and disconnect the speaker connector from the circuit board. The covers on the 780 are rather tight so you might have to gently pry the cover off with a small flat bladed screwdriver or something similar.
Next, take a look at the accompanying photo. It is the view with the scanner upside-down, looking towards the rear. As you can see, there is a large 18 ohm 2 watt power resistor next to where the internal speaker plugs into the circuit board. It is marked R413. This resistor must be shorted/jumpered to restore full audio through the internal speaker. You can short it in a number of different ways. If you are concerned about voiding the warranty, you can simply use a short length of wire with small alligator or “grabber” clips on each end like those commonly found at Radio Shack. (If you use this method, make sure the connections are secure so the wire will not fall off and cause a short circuit inside the scanner after reassembly.) Alternatively, you can simply solder a wire across the resistor’s leads or just remove the resistor and install a jumper wire in its place like I did.
The second fix is optional. It involves removing a section of the rubber gasket underneath the speaker. The center portion of this gasket blocks a significant portion of the internal speaker. Remove the speaker by removing its screws and remove the rubber gasket. Using a razor blade, Exacto knife or scissors, cut the center "bar" section out of the rubber gasket and then reinstall the gasket and speaker. Plug the speaker back into the connector on the circuit board and reinstall the bottom cover and four screws. If the rear portion of the bottom cover doesn't seem to fit correctly upon reassembly, you may have to loosen the screws on the speaker and slightly reposition the gasket under the rear section of the speaker.
That’s it! You’ll be amazed at the difference this simple modification makes.
J.T. Makatura
N0SGQ
Normally, the audio output level of the PRO-92 is attenuated quite a bit to avoid any ear damage when using an earphone with the scanner. Unfortunately, this attenuated audio level is too low to sufficiently drive an external speaker. This mod will allow full audio output when using an external speaker with the Radio Shack PRO-92 or 92A.
Work on a soft surface to avoid scratching the plastic window on the scanner.
In the picture you can plainly see the 3.3Kohm resistor used for the squelch enhancement modification (by James A Hoitsma, VE6JAH). This is not an error in placement. When using a ¼ watt resistor there was some interference when I reassembled the radio so I chose to mount it this way instead. The furthest left connection on both the volume and squelch controls are connected to the same point.
Finally, for those that may want it, I've included a picture of the discriminator tap point. Space is at a premium in this radio so you must be creative when you choose a mounting location for the discriminator jack. Pin line terminals would probably be your best bet.
Enjoy!
Joe
They are 5mm wide so you will have to file them down flat on both sides to about 3mm wide. You will also need to file the tip on one so the ribbon can side back in.
I removed a surface mount LED and replaced it with this new one. There was a little modification done to the backlight plate that sits behind the LCD. I was able to remove both surface mount LED's and just solder wires to the + and - pads. I tried just one LED in the center which makes it a little uneven.
Picture #1 (compared to VR-500 backlight)
I've added another LED and put them on each side of the LCD. It has more of an amber color and is a LOT brighter!
To restore the descrambler on the [US] DJ-X2:
Remove the back cover to expose the circuit board.
Find the short black wire.
At the end of the black wire nearest the battery you will see that it is soldered to one or two diodes.
If the wire is soldered to just one diode, simply remove the wire.
If the wire is soldered to two diodes, remove the solder so that there is no contact between the diodes (do NOT remove the diodes) and all the solder connecting the two diodes together while being careful not to do damage by overheating any components.
Remove the black wire.
Now you should be able to use the descrambler as described in the owner's manual.
NOTE: Keep in mind that actual use of the descrambler is illegal per federal regulations in the US! Penalties for being caught using such a device include stiff fines and jail time!
As we all know, LEDs in a scanner consume current, shortening the life of the batteries, even though the Tigerscan uses a single 9v battery. It appears that the LEDs may be the culprits. I performed this mod over a week ago and I'm still using the same alkaline 9v.
The mod involves opening the scanner and cutting both cathode legs of the two LEDs. You then jump each cut with a 47k 1/4W resistor. This will dim the LEDs while keeping them "useful", thus extending the life of the battery.
Take the bottom cover off and disconnect the speaker connector and set it aside. Position the radio so that it is upside-down with the front panel facing you. Look to the left on the lower circuit board for TP 301. It is a typical "test point" in that it is just a bare wire sticking up about 1/4" from the circuit. It is just to the left of the CN302 connector and just about directly behind the PROG and CLEAR keys on the front panel.
The Pro-2067 uses a 3361 series surface mount chip (IC301, underneath the upper circuit board) and TP301 is connected directly to PIN 9. Unfortunately, while the tap provides a clean signal, the voltage level available at the tap is a little low at .250 so some interfaces may need some adjusting to function properly.
There are also some very interesting signals available from another "test connector" that is readily available inside the scanner as if it were for some future add-on board. If you got a scope, check it out. I guess we'll have to wait and see what the future holds for this radio.
Finally, I checked out the tap with a few trunking programs and they all worked perfectly.
Remember, scan often and scan legally...Big Brother IS watching.
I removed the 4 screws holding the back cover on (2 inside battery compartment) and gently pryed the back off starting at the bottom. I then lifted the volume and squelch knobs off. Once inside I removed 2 silver colored screws in a metal bracket at the top which mounts the board assembly to the front cover.
I then moved the speaker wires located near the bottom away from a plastic clip they were in to add additional length for movement. I gently lifted the board assemblies up at the bottom just far enough to slide in the foam rubber (which I had cut by sight to fit just behind the speaker), and reassembled the radio.
Anyone who performs this enhancement should have had practice dissassembling delicate equipment, because the service loop in the wires is short and the fit of the board assemblies inside is very snug.
There is a trade off in reducing hysteresis and that and that is rapid chopping of the audio on signals that are near the squelch threshold. This is especially likely on mobile signals that have rapidly varying signals strength. The goal is to retain enough hysteresis to reduce audio chopping to an acceptable level and still remove most of the squelch tail. To some extent, the best compromise will depend on the type of signals monitored and the personal taste of the user. Connecting a 100K resistor in parallel with the original 470K chip resistor seemed to provide a good operating point. To add more hysteresis (and more squelch tail) the 100K resistor can be raised to 220K or even 470K.
The usual disclaimer applies to this modification. That is, modifying your radio will void the warranty. Performing this modification requires a certain amount of dexterity and experience with surface mount components. It is very easy to destroy components with a hot soldering iron and if you do so, it is not my responsibility. Although the circuit in other recent Uniden scanners will be similar to the provided schematic, there may be variations that would not allow the information presented here to be applied to other models. I have no information concerning the modification of models other than the BC895.
UPDATE: Although the resistor change in the original mod can improve performance, it has been found that the addition of a diode across the 470K resistor eliminates the squelch tail while retaining the hysteresis. Uniden has added this diode to the PRO-2052 and indications are that it will be part of the BC780 squelch circuit. The diode mod is recommended over the resistor mod unless you want to reduce the squelch hysteresis. A diagram has been added to show how to apply the diode mod to the PRO-2048.
BC895XLT Squelch Circuit Schematic
PRO-2048 Squelch Circuit Schematic
The following is a WAV file comparing the stock BC895 with the squelch diode modified version. There are three transmissions. The first is just a quick key up with no voice and the second is a dispatch. Both of these are with the unmodified radio. The third transmission is with the diode modification. For all three the squelch control was set near threshold and was not moved.
Remove the battery cover & battery pack. Remove the 4 screws from the back cover & remove the cover. Remove the speaker connector up the left side of the Rf board (white connector with black & white wires).
After removing this, gently pry up on this board just below the 22 pin connector on lower right hand corner. Flip the board you just removed over on its back and find the solder pads of the volume pot.
Trace the outer two circuits to just below the pads and you will find two surface mount components. The first, a black numbered resistor, the second a brown capacitor, just below the first numbered resistor.
Remove the brown capacitor, reassemble radio, and enjoy.
I assume no responsibility for any damages incurred while attempting this mod.
ADDENDUM: Brett Miller performed the above mod then created a web page with step-by-step pictures!
BUT FIRST A WORD OF CAUTION
It never fails that someone will stumble across even the simplest of
modifications and somehow manage to toast their scanner. I am hereby stating
that if you read this post and decide to tinker with that unit this will be
YOUR problem, not mine. If you break it, too bad. Not my fault, I didn't hold a
soldering gun to your head, now did I? I am NOT responsible if you kill your
scanner, OK? OK, on with it then...
NITTY GRITTY DETAILS
For those of you who know what your are doing and just want to know which pin
and chip, it's MC3361CN, Pin #9. Have fun. For those who need more detailed
instructions, read on below...
DISASSEMBLY
Uniden does not want you to do this.(Yes this is a UNIDEN scanner.) This is
evident in just how difficult the scanner is to take apart. You will need a
small philip's head screwdriver AND a butter knife or similar implement to pull
it off.
I don't think I have to tell you to unplug it first...but I will anyhow. Unplug it from the wall. Remove the battery cover and the batteries. It's also helpful to remove the antenna, just because it can get in the way during disassembly. Then remove the 4 screws that hold it together. You don't need to remove the belt clip, but I did just to keep it out of my way.
Now, using the butter knife, carefully run it along the edges of the scanner so that you can see a slight gap in the seam. Then use it to CAREFULLY pop the battery compartment area free of it's retaining flanges at the bottom. You'll see what I mean...
After about 5 minutes of fiddling with the knife, you'll get it free. Notice the large metal cover over the back half. Like I said, Uniden didn't want anyone tampering around in here. It's tempting to remove it, but don't bother trying - I did and found out that you can't - it's EPOXIED on! Fortunately, we don't have to mess with it.
Unplug the back board from the front one - it'll happen automatically when you pull it apart - just be mindful of the plug and don't bend those pins. The plug is located on the side opposite the power jack. Turn the board over and you will see the chip we'll be working on - MC3361CN. It's towards the bottom, right near where the speaker wires plug in. Can't miss it. I didn't bother to unplug the speaker, but you can if you want.
SOLDERING THE TAP IN PLACE
The pin we want to tap is pin 9, per Bill Cheek's scandata.faq file. I
confirmed it for myself last night - it works. Thanks Bill! For those who have
no idea which pin is pin 9, see the diagram below:(use a fixed width font to
view)
16 15 14 13 12 11 10 9 | | | | | | | | ----------------------- | MC3361CN | | | ----------------------- | | | | | | | | 1 2 3 4 5 6 7 8
Pin 9 will be in the upper right hand corner. I simply took apart an old mono earphone I had and connected the + lead of it to this point. The decode rate I am getting is OK, but nothing to write home about. I'm going to put a 1.0 uf capacitor inline to see if that improves things, and I am suggesting here that you do the same. So, on pin 9, solder the + leg of a 1.0 tantalum capacitor to it, and then solder the tap wire to the other leg. Then pick a ground point (the metal plate that the antenna jack runs thru is a good spot) and connect the other lead to it.
I then just ran the wires down and out where the batteries go, and let the plug dangle out thru the battery compartment. You will find it closes just fine with this cable in the way. However, those going for a more "pro" look will probably want to get a 1/8 mini plug jack and mount that in the case somewhere. Have fun - I'm too lazy for that. ;-) Plus, if the scanner ever quits for any reason, it's a simple matter to remove the tap wire prior to shipping it off for service. Sure it's ugly, but it works right?
REASSEMBLY
Other than being careful not to bend the pins on the main board as you plug it
into the socket on the other board, reassembly is fairly simple. Press the two
halves together gently until you hear it "snap" into place. Then put the
screws, antenna, belt clip and batteries back in and plug it into your favorite
decoder or PC sound card - whichever method you use for data scanning. You're
done!
LEGAL NONSENSE
Some people would get upset if their modification text appeared on someone's
web page, in a book, on TV, etc. I'm not one of those people. I could care less
who you give/sell/trade this info to or for what. More power to you. Don't get
mad though if I spoil your party by telling everyone where they can get this
info and more for free: Dejanews.com. If you would like to include it on a web
page (I can't imagine why, but hey it's YOUR page...) you have my permission if
you'd just be so kind as to mention who wrote it. If you don't, you can still
have it, I won't come after you or anything, but it would just be a nice
gesture. Thanks.
Hope that was helpful - I'm sure someone out there has a pro 91 and wants to do some data decoding with it! It works pretty good for that. Much easier than carrying a bulky 895 around!
Have fun...
On the underneath of the top circuit board near the battery connector there is a large surface mount resistor tagged 27R0. This resistor sets the charge current to 80mA. By soldering another 27 Ohm resistor in parallel, the charge current will double to 160mA. A 1 watt rating resistor must be used and it must be positioned off of the circuit board to allow adequate ventilation.
Transistor Q5 will heat up a bit more, so when charging, take the battery cover off and don't charge in hot conditions. If you are manually dexterous and have a small tip soldering iron, a heatsink can be soldered to the top of Q5 and also touch up the solder connections on the transistor and D21.
I have been charging with this modification for a few weeks and have had no problems other than the rear of the unit getting warm. Charge times become 14 hours for a 1600mA battery, and 7 hours for a 800mA battery.
I have taken some JPEGs of the modification which I can e-mail to anyone interested.
WARNING!! This mod will void your warranty.
For the time being it looks like the BC245 will not be sold by dealers in the UK. So a number of folks have gone down the same path as I did, a private purchase from a US dealer, in my case 'The Ham Station'.
Out of the box, apart from entering some cell frequencies, a base freq of 449.975 and an offset of 12.5, it was pretty well 'plug n play'. The only problem being the US 110v charger. I ended up cutting the lead off of the charger and fitting the lead to a UK 240V 12VDC 200mA supply. The wire with the white trace is the +VE.
I soon figured out that the external earphone socket had a limited output, and had seen some notes stating that if you shorted the external speaker ground to the radio ground, it restored the full earphone output. Also I have a requirement for a discriminator tap to run with some trunking software. So I decided to carry out both modifications at once.
To gain access to the inside of the BC245, remove the rubber duck, battery cover and carefully unplug and remove the battery pack. Remove the four screws that secure the case and remove the rear cover, easing the top of the cover away first.
Looking inside the scanner, as you look at the back, you will notice a small plug the looks very like the battery connector. This is the speaker connector. Carefully unplug it. Now CAREFULLY unplug the RF board that is facing you. It has a multipin connector in the bottom right hand corner as you look at it. The top of the scanner is on this board, so when it is removed, all that should be left will be the speaker. Set front and keyboard/logic board.
When you have removed the RF board, turn it over and look for the earphone connector solder points, the single connection nearest the board top, with a small chip resistor on it, should be shorted to a suitable ground. I used a land under a screw that secures the large metal can about 1/2 inch from the connection.
To do the discriminator tap mod, looking at the RF board, find the 16 pin chip marked MC3361CDR2. As you look at the chip with the printing on it the right way up, pin 1 will be in the bottom left hand corner and the rest of the pins are numbered in an anti clockwise direction. You want pin 9, which happens to be in the top right hand corner. Make a mental note of where this pin is.
Now look for a ground connection. There is one about 3/8 of an inch towards the board top from the 3361 chip. Now connect two 6 inch long hook-up wires to pin 9 and ground, they should be of 2 individual colours for identification. Carefully routing the hook-up wires to the bottom of the RF board, plug the board back in to it's connector, making sure that the speaker wires do not snag. Plug the speaker connector back in.
Drill a 3/32 hole to take a mini jack socket, on the case rear, below and to the rear of the 12V input connector (if you lay the case rear to the side of the scanner, you will see where the socket will and will not fit!). Fit the mini socket, connect the ground hook-up wire to the ground of the socket after cutting to length.
Connect the -VE leg of a 4.7µf 16V tantalum capacitor to the tip connection of the mini socket, and connect the wire from pin 9 to the +VE leg of the cap after cutting to length. Carefully dress the cap legs and wires so that there are no shorts or obstructions. Secure the capacitor in place on the case rear with melted candle wax. Carefully replace case rear, screws, battery and cover.
I have noted that the discriminator tap gives quite a low level output, which does not work too well with my two home made data slicers, but works 100% with a commercial data slicer.
The earphone output now works (in my opinion) as it should with an external speaker.
I'm very familiar with HTs and electronic stuff in general. Up until a few years ago, I used to spend my spare time in a local service lab repairing and modifying ham equipment. Now I have my own small lab at home just for personal use.
With a little luck, I have dramatically reduced the CPU noise problem and I would like to share my experience with your readers.
Evetually, I'd like it forwarded to the AOR people in the UK and US in the hopes they could replicate the modification in some fashion, thus making the AR8200 an even better receiver.
The CPU noise of the AR-8200 is a known problem, reported by many users. AOR has modified the CPU shielding on latest shipments in order to fix it. My AR-8200 is a recent S/N (071798) and it has the "improved shielding" from the factory (CPU board release "B"). However, using the portable antenna, there are frequency ranges where the CPU noise is still evident, and affects negatively sensitivity and scanning operation on VHF.
A simple test shows if the weak signal you are receiving is noisy simply because it is weak or because it is disturbed by the CPU: press and keep pressed the PWR key, as like as you should do to turn the radio OFF, but DON'T RELEASE THE KEY. The CPU, together with the LCD, is turned OFF but the receiver is still alive as long as the PWR key is kept pressed.
If the signal out of the speaker becomes clean, it means that it was disturbed by the nasty CPU noise. I made this test many times on many signals, and it has explained why my AR-8200 wasn't able to receive the many signal my tiny IC-R2 receives crystal clear.
Well, I had the courage to open my maaaaany-bucks AR-8200 and I've practically solved this problem. If you have the same courage and enough skill in electronics, you have a good chance of achieving a similar result.
DISCLAIMER:
The following procedure doesn't involve any modification in the circuitry nor component change in the AR-8200: it's just an improvement of ground paths routing. However, opening any radio for any reason without being a qualified service technician for that radio brand normally voids warranty. Moreover, technical skills and familiarity with miniaturized electronic equipments are required to complete successfully this procedure without damaging the radio. I'm giving no warranty that the CPU noise problem on your AR-8200 will be 100% solved, but my experience on mine has been fine and I wish to give the same opportunity to the readers. Since I've no way to repeat this modification in other similar radios, I would appreciate to get some feedback about its effectiveness.END OF DISCLAIMER
MODIFICATION:
THIS IS A CRITICAL OPERATION: you may stress the mechanical controls of the radio. While pulling, the side panel (that shield-shaped plastic piece with the rotary dial, FUNC key, arrow keys etc...) must be kept together with the front panel, and the top panel (the one with the VOL and SQL controls) must be kept together with the back panel. Once the two portions start getting separated, always check that none of the rubber dust caps goes back in its hole, otherwise you cannot separate the two parts totally.
Place the opened radio on a clean, flat surface with the BNC and the two VOL/SQL knobs towards you. The two portions should be side-to-side along the connectors side: the front portion is on your left, face down, and the back portion is on your right. Be careful not to stress the two ribbon cables that connect the CPU PCB to the RF PCB and to the OPTION PCB.
On your right, the back portion holds the radio section (two stacked boards) and the Option Board that also includes the battery charger circuit and the computer connection. You will notice that a large area of this board is covered by GND layer, and it has a large notch where a VERY big resistor is fitted. Below this resistor, a small Z-bent metal bracket fastens the radio section to the plastic case by a small screw (let's name it as "screw A").
Actually, the Option Board is providing the majority of the CPU noise radiation, likely because the only provided GND return is the highly-inductive path through the ribbon cable.
The radio section has a small metal frame that holds the pots and the BNC connector. Next to the Volume pot, this frame is bent and has a threaded hole where fits one of the 7 screws that normally keep the radio assembled. Let's name this hole as "hole 1". Its counterpart in the front portion of the radio is a hole in the plastic case, close to the wrist strap anchor. Let's name this last hole as "hole 2".
To do the first connection you must solder one end of a 20mm long bare copper wire to the GND layer of the Option Board, and squeeze the other end under the head of the screw "A". Since this wire must be straight and as short as possible, I have scratched a 2x2mm area of the solder mask (that green paint that protects the PCB) from one of the two "flaps" who hold the big resistor, exposing a copper spot of the GND layer.
IMPORTANT: none of the big resistor terminals are at ground, neither are any of the nearby components or vias! The only way to get a ground access on the Option Board close to the screw "A" is to scratch off a small solder paint area.
The second connection requires a little more work. From a 0.2 mm copper (or brass) sheet, thin enough to be cut by ordinary office scissors, you must cut a small 4x8mm strap. Figure it in your mind as composed by two 4x4mm parts, and drill a 2mm diameter hole in the centre of one of these two ideal parts. Since it is very difficult to drill a hole in such a small piece of metal sheet, I suggest, as I did, to first drill a 2mm hole in a larger piece of copper sheet, and after to cut around it the 4x8 mm rectangle.
Align the hole of this tiny copper strap you built against the inner side of the "hole 2", while bending the strap in "L" shape to overlap 2 or 3 mm of the CPU PCB GND layer. Mark this small overlap area of the CPU PCB and CAREFULLY scratch off the solder mask to expose the GND copper. Pre-tin this area and then solder upon it the horizontal part of your tiny L-shaped copper strap, while keeping the vertical part aligned and pressed against the inner side of the "hole 2".
To complete this operation, a temporary-screwed 1.5mm screw + nut in "hole 2" can be helpful to keep the copper strap tight and aligned in place. Be quick in soldering (but be sure to make a good solder joint) and be careful to not damage the radio plastic case with the soldering iron. If you made a good job, when the radio is reassembled, this copper strap will provide a direct electrical connection between the CPU board GND and the "hole 1" in the radio section.
That's it. Now it's time to check on known weak signals how effective the modification has been. Thus repeat the "PWR key press" test described at the beginning on the same signals where you have noticed the CPU noise.
Copyright © 1999 by Giovanni Benenati
Usual disclaimers apply - should you decide to carry out the following modification, you do so at your own risk, and I take no responsibility for damage to you or your scanner as a result. However, I *have* done the mod and it's a piece of cake - it takes about five minutes in all, and is a great "first mod" for those who, like me, have rarely ventured inside their equipment!
All you'll need for the mod is a cross-head screwdriver and, perhaps, a thin knife. Here goes:
1) Turn power OFF
2) While pushing the following keys, turn power ON:
BAUD RATE KEYS
-----------------------
9600 ENT + 5
4800 ENT + 6
1200 ENT + 7
300 ENT + 8
| Copyright © 2002 by Richard J. Wells |
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