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Tricks of the Trade

Soldering a flat pack IC - submitted by Rog

A propane soldering iron that has a hot air attachment works great and puts heat in a small area without effecting surrounding components. Heat the IC, not the legs. It's not ideal in all cases if you want to reuse the IC. Caps, diodes, resistors and transistors are okay. Clean the pads with desolder wick and apply flux, next align the IC and solder the corners to keep it in place, affix the pc board at a high angle for each side you want to solder, apply solder at the top leg in large enough quantity to were it wants to run down the legs of the IC ( flux is very important for this to work correctly). Follow the ball of solder with your iron down the side of the IC as the solder runs down. Clean up the excess solder on the last few pins at the bottom. This will leave a factory looking solder job. Repeat this for each side of the IC. It may take a little practice to get the angle just right, but once you figure it out, soldering a flat pack will take no time at all.


Replacing the HOT - submitted by Hille

Substituting a HOT is a tricky business as explained in countless repair articles, so use my advice at your own risk. I provide this information only as an example of the reasoning process I used to successfully replace the HOT in a monitor that I own. In servicing this 19inch Monitor, I discovered the HOT and its current limiter FET both dead. The FET was cheap and readily available from a large catalog order distributor, but the HOT turned out to be an expensive hard-to-get 1500V 12Amp non-IDD BJT with no (free) detailed data. Having no schematic, I checked all semis and passives around the flyback, HOT, and E-W circuits, and found an open power resistor in the HOT base drive circuit which I speculated to be the primary cause of the destruction. However, I decided that a low-cost, easily obtained substitute of the HOT would have to be used in case I was wrong. In order to determine the HOT parameters I couldn't find, I first determined that the Hdeflection and HV flyback were not separate circuits. With a specified H-scan rate up to 96KHz, the HOT could be subjected to a 10usec cycle, and thus would have to be a newer generation (at the date of the monitor's manufacture) BJT with high peak Ic and the faster Tstg / Toff times of around 2usec and 0.1usec, respectively. Filtering for the parameters I learned of the original, I found a sub based on this reasoning in the readily available BU2527AF, a relatively inexpensive high performance non-IDD BJT. As a bonus, the monitor maker had provided a second mounting hole to accommodate the slightly different SOT-199 package of the sub (manufacturing option, no doubt). Replacing the HOT, the FET, and the resistor yielded a working monitor with a steady, bright display that doesn't overheat or shut down. I haven't touched the base drive circuit at all, so I'm not sure if this was just dumb luck, or the monitor design has good margins, or perhaps the substitute happens to be a dead-ringer for the original. I haven't scoped around the flyback, but the excellent picture and monitor behavior would suggest that I don't waste my time. The only mod I made was to upgrade the rating of the failed resistor by a factor of 2.

 


Temporarily repair a worn down pinch roller - submitted by Gilbert Desmarais

This tips works fine only if the pinch roller is glossy and/or with pits. If there are radial cracks near the borders, it will not work properly. Press the pinch roller between two fingers and look if radial cracks become visible. To give a second life to the pinch roller of a VCR or a tape deck, use a very fine grain sandpaper of at least 1000, 1500 is better. Take the pinch roller with your fingers and roll it on the sand paper on a hard leveled flat surface. The movement of rotation on the sandpaper needs to be in the opposite direction of the movement of translation. If it is not done this way, the pinch roller will only roll without any effect. If the pinch roller is locked in the same position, it will be oversanded in one area and not sanded in other areas.

 

An alternative way to use the sandpaper is to cut a small piece of it, hold it in one of your hand and pass it over the pinch roller that is held with 2 fingers of the other hand. In all cases, don't overdue it, stop when the glossy appearance and/or the pits disappeared.

 

Another way is to fix the pinch roller to a lathe and pass the sandpaper on it while it is rotating.

 


Repair worn carbon rubber contacts - submitted by Gilbert Desmarais

1) On some models, the carbon rubber is thick enough, only the surface has lost his conductive properties. Use a very fine sandpaper, like 1000 grain, and gently remove the old surface of the carbon rubber to expose the new surface. This tip doesn't work if only the rubber surface coated with carbon. This tip work fine if all the rubber has the carbon mixture incorporated in it.

 

2) Salvage an old or cheap calculator keyboard. Cut the carbon rubber contact's tip from one key and place it on the other key, from which the defective rubber contact has been removed. I found that one of the following glue methods works fine, depending on the rubber material pure silicone sealant (for bathroom) or 5 min. Epoxy glue, 24h epoxy doesn't work. The glue needs to stay flexible when hardened.. To select the appropriate carbon rubber contact, it is best to make measurements directly on the exposed surface, with the two tips an ohmmeter to find a similar resistive material. This is because some circuits use a current or voltage comparator circuit. So if the resistance is too low or too high, the circuit could make false triggering of the corresponding key.

 


Custom build a VCR belt - submitted by Gilbert Desmarais

A way to build a custom belt for VCR, is to use an old bicycle tire tube. It can be cut in circular strips with the desired width. It can also be cut in angle, to obtain a different diameter length. This tip only work for belts that are not timing sensitive, like the loading tape belt, because a lot of circumference imperfections are present.

 


HK shorts in CRT's - submitted by Nicolas Cannonne. Nicolas is a member of our email discussion groups.. All subscribers have access to his, as well as over one hundred other technician's comments and expertise.

This is useful when you have a CRT short from any cathode to heater. The aim is to apply an ungrounded voltage to heater pins. First cut all traces that goes to the heater pins on CRT board. Then take a wire, make one (or more) loop around FBT core and apply the 2 ends of the wire at the enter of the schema. This signal is something like AC signal going from –10V to +15V at the Horizontal frequency rate. So the diodes avoid any negative voltage, the caps are doing a nice flat 15VDC and the regulator make the 6.3V required for the heater. The LM317 has to be mounted on heatsink. I have added one more diode in input just to drop 0.7V.The less the input is the less the reg heats. Connect to 2 output pins directly to the heater pins on CRT board. First thing to do is to check with your scope the output voltage of the wire looped on FBT, may be you’ll have to do some additional turns to increase voltage. You can replace the 1K resistor by a 5K pot to adjust the output voltage. Heater usually draws something like 1A. This has saved 3 Trinitron CRT for me. This works for multisync monitors. 99% of the monitors I have seen are using a DC voltage for filament. Thanks for any feedback if it doesn’t work for you.


Repairing leaky flybacks - submitted by David

Burn hard black plastic material to stop the leaking. You can use silicone, it works too.


Depopulating old circuit boards - submitted by Jeff Roberts. Jeff is a member of our email discussion groups.. All subscribers have access to his, as well as over one hundred other technician's comments and expertise.


 

We have a solder pot, it is a ring of stainless steel about 8 inches across welded on top of a base plate of regular iron. Try to picture an 8-inch circle of iron (solid across the diameter) then picture a large ring, also 8 inches across but only 1 inch wide that gets placed on top of the solid piece. Weld the ring to the plate around the INSIDE of the ring so it becomes a reservoir. Buy bar solder from the hardware store, usually used for sheet metal work, about $8.00 Cdn per bar. Place the plate on the burner of a stove, it is about the same size as one of the small burners, and turn the burner to medium, add a couple of bars and in no time at all you have a pot of molten solder, place any old circuit board across the top of this rig and it unsolders all of the components that touch the reservoir at the same time, you merely place it down and start pulling parts off with your pliers, you can depopulate a monitor circuit board of all it's valuable parts in about 2-5 minutes once you get the hang of it. You can breakdown/depopulate 20 monitor boards and do the cleanup and preliminary sorting in a 6-hour shift. You won't need to buy parts unless it is something special, like a Sony IC or a strange video driver. My transistor bins are all full as are my capacitor bins, thyristor bins, bridge bins, coil bins, and IC bins. I have cross reference books so I can always find a good sub from my own stock.

 

CAUTION: Wear heavy clothes, long sleeve shirts, goggles and gloves. If a capacitor falls off a board and lands in the pot and goes unnoticed then a minute or so later it will explode!! And you get solder everywhere (yourself, ceiling, walls floor etc.). So you have to be careful. It also smells bad, because the materiel that the circuit boards are made of does not like to heat up like that, fiberglass boards are OK but pheolic smokes and stinks bad. We have a large fan in the window to exhaust the smoke and we open other windows and doors to keep the air fresh.

 


Riveted mode switches for VCR's - submitted by Roger Lonnkvist

Replace or toss the machine! Get a jar with a screw-on lid (have had success with a sealable plastic parts bag too). Drop in the mode switch, spray in a cleaner spray that has oil in it (Nu-Trol for one) to just cover the switch and let soak for 24 hours. Remove from jar and spin with a screwdriver, repeat if necessary, dry and wipe off. To be creative, put a piece of thin foam in the bottom of the jar, drop in the mode switch so that a slot or gear is up, drill a hole in the lid for a screwdriver, cover with fluid. Drill a hole in the lid for a screwdriver, cover with fluid, soak and then insert screwdriver, push down and spin the shaft under the cleaner fluid. To preserve the fluid for reuse, use a second lid or seal original with tape or a screw with a rubber washer. Can be adapted for other carbon or brass wiper devices.

 


Replacing EEPROMs in RCA's - submitted by Paul Worthen

When replacing the EEPROM in an RCA set, sometimes the horizontal is so far off frequency, it is hard to see the parameter number when going into the service mode. To make the numbers visible, switch to the alt input, or disconnect the antenna. With no video input, the number will be clear and stable.

 


Cleaning capstan shafts and rubber pinch rollers - submitted by Paul Worthen

Use "Scotch Brite" scouring pads. They are usually available at Home Depot, in the paint department. The pads are plastic, therefore won't damage the cap shaft and have the scouring power of "00" steel wool.

 


Removing labels to reuse - submitted by Eric Richards

When you replace a broken back with a new one from the manufacturer you find that there are no labels such as Model number or serial number. If you freeze the label you will break the glue bond and can take the label off the old back with no trouble and if you are lucky you can stick the label on to the new back with out applying new glue.

 


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Removing labels - submitted by Eric Richards

Use CRC oil to remove old labels. Let it soak in for 15 to 30 minutes and most labels will then easy peal off.

 


Solder wick for FBT and rivets - submitted by Eric Richards

Wrap the braid around the FBT pin and press the solder iron on top to soak up the solder. Works better sometimes than plain (or heated) solder suckers.

 


Cleaning Capstan Spindle - submitted by Eric Richards

Your Fibre glass pencil used for taking paint off PCB tracks can also be used to clean Iron oxide off VCR capstan spindle, but you may prefer to use brass refill. Saves a lot of time compared to using IPA.

 


Capstan Roller Refurbishing - submitted by Tony

A great repair for capstan gone shiny or slippery is have the roller on the capstan arm to hold it even with a small grinder. Turn on the grinder, switch it off right away and let the roller spin at about a 10 degree angel to freshen up the rubber just like new. Quick repair and it lasts if the rubber is not dried up too much.

 


Plastic Repair - submitted by Ron Reyn

I have used this on many occasions to repair plastic parts that would not glue together for strength. This repair makes the part stronger than the original. The repair material can be a paper clip because it is so easily workable, or a lead cut off a small value capacitor or off a 1/4 watt resistor.


What is DAS and why do I need it? - submitted by Kurt Hanson. Kurt is a member of our email discussion groups.. All subscribers have access to his, as well as over one hundred other technician's comments and expertise.

As time goes by, more and more monitors are being built with microprocessors or microcontrollers incorporated in the circuitry. The use of these controllers allows for more user/servicer adjustment options at a lower manufacturing cost. This increases the profit margins of the manufacturers. These processors were once only found in the expensive Sun, Sony, Taxan monitors, used in desk top publishing/CAD businesses. Now they are in virtually every monitor made today.

The modern (post 1994) CRT's are "weaker" and do not last more than a few years, without losing picture quality. (Grey scale or white balance, focus and brightness.) These CRT changes make it necessary to readjust them by using some sort of Digital Alignment System or DAS. Sony DAS is not new. It was first used or designed in the middle to late 80's. It is a way to change or rewrite data bits into registers that are processed by the controllers, using simple, basic serial communication.

Sony's DAS system is protected from piracy by using a "key" installed on LPT1, or printer port. This "key" must be installed for the DAS program to initialize. I have been using the Sony system since 1991. My DAS system was put together for almost $10,000. I am Radius, HP, Compaq, Sony, Apple and Digital certified for component level repair... I have worked for a big corporation for a long time now. I certainly couldn't afford that amount on my own.

I understand that you can get the basic DAS system (software and hardware) for under $1000 now. My system is NOT basic! I can do DAS adjustments on most all monitors now. Major brands at least. Some are certainly not worth the time though.



Cleaning Tape Drives - submitted by Dave Campbell

A common mistake in tape deck repair (both audio and video) is to use the fluid supplied with cleaning tapes or cleaning kits (OR alcohol). Most cleaning fluids contain mostly alcohol. Alcohol is BAD for rubber parts. It actually makes them get harder. Not only should we be cleaning off tape residue, but we should also be softening the surface to better grip the associated idlers, capstans and especially the pinch rollers. Houshold Ammonia works infinitely better for all rubber parts. You will find it nicely softens as it cleans. You can even soak parts in it. It will not degrade the rubber as many solvent type cleaners can. DO NOT clean the heads or metal parts with it as it IS corrosive. If you religiously clean the pinch rollers with Ammonia you will see a marked improvement in the performance of all tape drives and many less machines that eat tapes.

 


Keeping track of screws - submitted by Mark Melvin

The idea is to sort the screws and miscellaneous metal hardware in such a manner that when it comes time to reassemble there is no guess work. Cut a square of cardboard about 6" by 6" or 8" by 8" or 6" by 8" or whatever size is appropriate for the type of electronics you disassemble. Glue six or eight magnets about one or two inches apart to the cardboard. Glue in rows, in columns, or any order. It doesn't matter if you use square, rectangular, or round magnets. Radio Shack carries a good selection. I prefer to use the round ones with hallow centers. Next, take the same number of "post-it" notes and cut them into strips using the sticky portion of the note. Begin to disassemble the device. Place the first set of screws on the first magnet and record their location on the "post-it" note label. Using the adhesive label stick the label to the cardboard or secure the label with a tack to the cardboard above the magnet holding the screws. Continue to disassemble placing each subassembly's screws on a separate magnet with the attached label. If you run into a nylon screw/washer place it into the center of one of the round hallow magnets (using the magnet as a cup). Use smaller magnets for smaller screws and metal hardware; use larger magnets for larger screws and larger metal hardware such as pinch roller arms, etc. The screws and metal pieces are neatly sorted by assembly and secured to the magnets. You can gently pick up the board and move it to a safer location knowing that after one hour or two days or two weeks the screws will go back to where they came from. If you plan to move the board place a "post-it" note identifying which unit they came from. And remember, some of the devices or subassemblies you work on are sensitive to external magnetic fields so use common sense in keeping the 'mag-board' a safe distance from them.


Cleaning Video Heads - submitted by Phil Bader. Phil is a member of our email discussion groups. All subscribers have access to his, as well as over one hundred other technician's comments and expertise.

If you can visualize a Mr Coffee filter, cut down the side ribs to the round center,about every third rib. Will end up looking like flower petels,now,cut out the circle at bottom, detatching the petals. Holding a dozen at once, you end up with many little square wipes and some larger round ones. They are food quality, so no dyes or contaminates, lint free, slightly abrasive,and very cheap!

 


Scope ESR - submitted by Michael Mayerhofer

If you have a scope and a signal generator you can easily build something like an ESR meter. All you need is two resistors, three BNC jacks and cable. I feed a voltage divider (2.7 KOhm in series with 5.6 Ohm to GND) with a 100kHz sinus signal from a signal generator. The scope and the capacitor probe are connected in parallel to the 5.6 Ohm. During measurement the cap will be in parallel with the 5.6 Ohm resistor and decrease the output amplitude of the voltage divider. Adjust the the signal generator to get maximum amplitude in the 5mV/div range of the scope. I use three resistors for calibration 1, 3.3 and 10 Ohm. Connect the resistors to the capacitor probe and make points at the side of the screen to mark the decrease of the amplitude. As capacitor probe, use the cables of an old multimeter. Mount the voltage divider and the BNC jacks into a little box which is directly connected to the second input of the scope. When checking for bad caps, just switch on the signal generator, change to the second channel of the scope and everything is ready. This method does not give you a direct reading of ESR, but you easily can estimate the ESR from the amplitude of the displayed sinus. The lower - the better. If you don´t have a signal generator, you could connect a filter to the calibration output of the scope and use this as a source. The calibration output usually has a lower frequency in comparison to 100kHZ where ESR is specified, but nevertheless, it should be suitable to identify a bad cap. I started to use this technique when I did not even know that ESR meters were available and I got used to it. All I actually do is press two switches and watch the amplitude on the scope as you watch the needle of your ESR meter. See picture below.

Eliminating Cockroaches - submitted by Steve Hagensicker 

Several years ago, when I was confronted by my first cockroaches, I followed the procedure with the Raid and a garbage bag. When I realized this did not kill them all, I tried something else as I knew I would run into more in the future and I do not want them things around my house! The next time I came across cockroaches, dozens and in all sizes, I decided to try the freeze method. As cockroaches seek heat, I figured they are probably delicate where cold is concerned. I took one large dude and placed him in a sealed Bell jar. Next comes the freezer for a 15 minute test. He came out looking dead, but I let him warm up and found he was only dazed. Next time was a half hour. This time he was very dead! Now that a time had been established, I was confident of a simple cure. As I had a fresh, dead one to examine, I went to roll him over with my forceps. I noticed his antenna being attracted to the forceps as they have a slight magnetic charge. Hmmmmmmm....... cockroaches like heat. Transformers and power supplies give off heat AND magnetic fields. I have come to the assumption they find electronic components by their magnetic fields. (Just a little info for you). Anyway, the cure? Plastic garbage bag with the mouth rolled up to the VCR and then taped shut. In the freezer for 24 hours!! Never had a live one after that! (It has also never harmed the VCR's).

submitted by Eric Richards

Use a can of oil spray like CRC 2-23 or CRC 5-56 used in most TV & VCR workshops.