| QUESTION NO. P21803-8: I know E.B.C. is emitter, collector, base. What does S.D.G. stand for? I am working on car amplifier and have problems determining blown chips with multimeter. I am aware that you cannot test these chips with this meter but I need to know what the gates stand for. I do not have name of chip here, due to me not being home with them. it stands for i think its single, drain, gate but not sure. |
|
The S, D, G stand for source,
drain, and gate. This is for a FET, a field-effect transistor, not a
bipolar transistor (EBC). Assuming that it is a power Mosfet, and not a
small JFET or UHF Mosfet, it will probably be an enhancement-mode
device. With a power Mosfet, you should find infinite resistance between
the gate and the other two leads, unless it has shorted. With the gate
externally shorted to the source, you should read infinite resistance
from drain to source, and read a diode junction from the source to the
drain. If you try to do this second test, without first connecting the
gate to the source, random charge that had accumulated on the gate might
affect the readings.
|
|
Simply put its source drain gate.
Extreme care has to be taken when testing those as they are high
"resistance" devices using an insulated gate or control pin.
If you bias the gate incorrectly IE with a meter probe the device will
fail. more info try http://e-www.motorola.com/brdata/PDFDB/docs/AN211A.pdf,
they have a fairly simple description of construction.
|
| QUESTION NO. P101102-9: What is meant by RF filters and what does it contain? |
| RF filters are usually discrete components such as capacitors, resistors and inductors which are connected in such a way with certain specific values to create a series, shunt or tank circuit which allow certain frequency ranges to pass through but reject other frequency range signals. For more info any public library in your state/province would had electronic theory books which will have chapters discussing such a topic and would have a glossary of terms. You can also look this up at www.repairfaq.org. |
| QUESTION NO. P1121-1: We are looking for the name of the company (phone # or website too) that puts a "M" in the middle of a circle. The "M" has it's legs, kind of curled inward on the bottom also. We have a small DC brushless fan that is bad, and this company has their sticker on it. We need to get a replacement. |
| www.elnec.com/ic_logos/ic_logos.htm. |
| I believe that is one of the trade marks for Motorolla. |
| That logo is Matsushita Electronics, the parent company of Panasonic. |
| QUESTION NO. P1129-3: We produce a circuit board to be used by blind, deaf or vision impaired computer users that can convert word documents to brail output device or to voice via voice modulation circuitry and software. The problem we have been having is revolving around a 3.3v to ground short that we cannot locate. We opened and isolated the 3.3v circuitry on the card and every time we believe a solution has been found our fluke continuity meter mocks us at every turn. We are operating under the assumption that our pcb supplier is testing the bare boards in QA analysis before shipment as promised. |
| Static testing with a continuity meter may not be as effective as tracing the current flow into the short, while under power, with a current tracer. Professional current tracing instruments are expensive, but if budget is a consideration, consider putting together a testing module, with a precision opamp (low Voffset). For a few dollars, such an opamp can be rigged up (using a 9V battery floating power source), with feedback resistors selected to give a 1000X amplification circuit. The idea is to measure the tiny (mV) voltage drops along the PC board traces, as the current flows into the short, by connecting test probes from the two inputs of the opamp, to various points along a given PC trace, and using the amplified output voltage reading to detect the direction of current flow. The output could be monitored on your Fluke meter. Achopper-stabilized opamp would probably be best, with their miniscule offset voltages and drift. Digikey (www.digikey.com) carries Linear Technology's LTC1152 & LTC1050 opamps, for example (get datasheets and design notes at www.linear-tech.com). Diode protection of the opamp inputs, and a capacitor across the feedback resistor, to attenuate AC amplification, are probably good ideas. |
| QUESTION NO. P96-9: Repairman looking for a camcorder school. Anyone out there know of a good one? |
| You may want to try Sencore at 1-800-SENCORE. They make the specialized equipment you would need. Hopefully they have the course you need too, or could refer you to someone who does. |
| QUESTION NO. P525-8: I need a source for service/repair manuals for CDRW's. Specifically Yamaha and most importantly the CRW4260TXPW. |
| Try the manufacturer direct or cross reference the FCC desiginated number for original device manufcturer and try with them. Much of this type of information is non-existant except in generic modes. |
| QUESTION NO. P31-6: I have a manual for building an electronic piece of equipment which contains a PCB. The manual says the PCB is a Universal Board but does not say where it can be acquired. Is there a supplier that manufactures Standard, Universal PCB's that can be adapted for general use in multiple projects? |
| Hm....Well about the only type of universal board I know of is perf board. Radio Shack carries such board with copper around the holes for easy soldering. |
| Radio Shack has an experimenter's kit that allows one to generate their own pcbs but the product is rather limited as to its applications. The quality or the generated pcbs area direct results of the experience and expertise of the person using them, especially with due regard to artistic ability. Other companies, such as Jamesco, etc used to make the blanks available with masking materials and echent fluids. I do not know if the material is available any more or if the EPA has added the chemicals to their dangerous list. Custom-made boards are available via many companies but the cost is rather out of sight for the average experimenter. |
| QUESTION NO. P222-6: How does one test FETs using a VOM? |
| You did not state if the FET is in the circuit or out. And assuming it is a MOSFET, if the FET is out of the circuit, gate to source resistince should be many megohms, both polarities. An N type Mosfet will be several megohms with the ohmmeter positive lead on the drain if gate and source are connected together and to negative lead. Reverse the leads and read a diode drop. |
| QUESTION NO. P22-2: How does a vaccum fluorescent display work? |
| A vacuum fluorescent display is like a triode vacuum tube, having anodes, grid, and cathode filament. For example, each segment of a seven-segment character will be a separate anode. Grid voltage creates an electron flow from filament to anodes. The electrons go to those segments given a positive potential, and fluoresce a phosphor coating. Segments that are given a negative potential do not receive electrons, and do not light up. The different lit/unlit segments allow a character to be seen. Go to this webpage, www.futaba-na.com/VFD/vfdframe.htm if you want more technical details of operation. |
| QUESTION NO. P98-3: I need to understand how a Switching IC, in particulary STK730-020 TV (NTE7126) operates. When I crosses over this IC to the NTE Equivalent, and referred to their illustration, I was given info like TR1Drain/Source Error Detection, ETC. Also, refresh my memory, the voltages listed on the inside of an IC Diagram (H.W. Sams Schemetics) where each pin comes out; is that the voltage that should be leaving the IC, or entering it? |
| Voltage does not enter or leave the pins of an IC. It is the potential that is present relative to ground. |
| QUESTION NO. P730-7: We are a small repair shop, just getting into SMT repair. Having trouble identifying some of the components (mostly discreets-transistors, diodes) to find suitable replacements. It seems that many of these parts have mfg. codes printed on them. Is there a guide that contains all of these mfg. codes and possibly some suitable cross references for these parts? Is there any way to easily identify these parts? |
| Some of the SMD id maekings are product and mfgr specific. Others are generic and readily available via parts houses. Best recomendation is stay with the manufacturer serrvice literature and supplied parts unless you are absolutely certain the generic will work. There are very good descriptions about the different types of devices in the service literature supplied by comanies like Sony, Hitachi, MGA, etc. |
| I do not know any guide that covers ALL the marking codes, and the codes have no standardization, but a useful lookup site for many SMD codes, including discretes, is www.marsport.demon.co.uk/smd/mainframe.htm. |
| Nte 2406 will work for surface mount NPN,NTE 2407 for PNP. You may need to compare case numbers with another transistor on the board to verify NPN or PNP.Resistors use a code whereas the first and second digits are significant and the third number tells how many zero's. For instance 123 would be 12 followed by three zero's 12K. |
| QUESTION NO. P730-1: How can I invert a video signal? |
| Emitter follower amp sta ge, properly designed, will do the trick. |
| An emitter follower does not invert video signal. try using a common emitter amp [inverts signals 180 deg.]. |
| QUESTION NO. P45-4: I have seen mentioned "Thompson/SK" as a source for power supply parts. Who are they and where to I find them? |
| You are referring to the SK series of universal semiconductor replacements made by Thomson Consumer Electronics. You obtain these through one of their many distributors; for example, MCM, Mouser, or Newark Electronics. To find your replacement, cross-reference the part number in the (cheap) Thomson/SK catalog, and use the substitute indicated. Or the distributor can look the part up for you, if you don't have the catalog. Two other series of universal replacement parts are the NTE and ECG series semiconductors. These outfits also have websites for product lookup, at http//www.nteinc.com/ & http//www.ecgproducts.com/. |
| QUESTION NO. P315-6: Does anyone have a phone number or address for Beckman Instruments? |
| For electronics test equipment, Beckman Instruments became Wavetek Corp., 800-851-1198 or www.wavetek.com , and Beckman Instruments for medical and bioscience equipment became Beckman-Coulter, 800-233-4684 or www.beckman.com. |
| QUESTION NO. P16-5: Is/Are there any other (inexpensive)means to buck 120VAC down to 90VAC other than a variac/auto-transformer at the power requirements I need? Currently I have a 2,900 vac UTC power transformer/power supply for a 2,000 watt amateur radio transmitter. It provides either 2KVDC or 4KVDC depending on how I connect the primaries (limited to using 120vac). I need 3KVDC, but to get this I am now using a 10 amp variac for test purposes only. Is there another method to drop 120 vac to 90 vac (to connect to the power xfmr primary) to get the desired voltage output? |
| May try a totally resistive load of very high current power resistors, or a number of light bulb in series. Go back to your basic electronics and determine what amount of current drop and therefore the necessary resistance required. Also, a means of dissipating the resulting heat being generated. |
| It might be better to use a TRIAC type light-dimmer circuit, that some resistive method. Assuming that you are talking a DC input power of 2kW (max legal power), your full power key-down plate current will be 667 mA. You want to drop the plate voltage from 4kV to 3kV, so this means that you must dissipate 1000V*667mA = 667W!! This makes your overall efficiency very very bad. And, a resistive method will NOT work anyway, as between transmissions, the unloaded plate voltage will peak charge to 4kV anyway. You need a proportional method, like your variac - a heavy duty 15A motor speed controller (not a cheap 600W light dimmer) should work. You will also need to provide EMI filtering for the AC input, to keep the commutation noise from getting onto the AC mains. You will also need to pay attention to wire lengths and routing to keep this EMI junk from showing up in your output spectra. Ah, the joy of being a ham...N9KFC |
| QUESTION NO. P123-6: What is the working frequency of the EIMAC 304TL tube? |
| Eimac 304TL operating freq at full ratings is 40Mhz. Driving input power of 11 to 52 watts with output power of 250 to 1100 watts depending on class of operation. |
| The Eimac 304TL can be used at full ratings of 1200-1400 watts output up to 40 Mhz. It can also be used at reduced plate voltage and input power up to about 80 Mhz according to their power grid tube reference catalog. |
| An excellant article on testing ordinary transformers for shorted windings with a schematic of a circuit appeared in Popular Electronics magazine. Copyright restrictions prevent us from reproducing it here but you can see it in: Popular Electronics, Aug.1997, Vol.14, #8, pp.67-72, with the circuit appearing on p.68. William Braell of Harvard Medical Center reports that he has built the tester and that it works very well. |
| QUESTION NO. P930-9: Is there an impedance matching device to able me to use a ceramic cartridge with a magnetic cartridge imput. |
| Ceramic to Mag input requires three
things. 1. Ceramic cart is high Z (impedence) 2. Cermaic cart is high
voltage 1- 2 volts 3. as a voltage generator has much different source Z from
magnetic Cart. If fidelity is not an issue simple resistive divider will
do. Ratio of 1000 ohm to 50 ohms will do. C<1000>----|----->Mag input> ^ 5 0 GND. If fidelity is issue then loading with .01 to .1 cap across 50 ohm resistor will reduce the highs in the ceramic cart. All must be shielded and audio ground used or hum will be present. Can be done with RCA to RCA in and out on small metal box. Double circuit for sterio. Years ago small high Z transformers were avaialble to convert Crystal and Ceramic Carts to Mag input. |
| QUESTION NO. P926-7: Regenerator "MUTER BMR95" correctly regenerates about five CRT (try about 40), sometimes the regeneration does not hold. There is a deterioration of CRT performances. Does anyone use this type of device without any problems? In the case of white flaws or concentration/ G2 default there is no effect, did you find a solution for recovering these CRT? |
| I have run into the same problem for 20 years with numerious brands. Some techs claim they work great, I myself have never been able to get more than 1 out of 40 to work. I wish you luck, but never trust a restored crt. When a newer crt is bad it is bad. |
| QUESTION NO. P911-8: How do you become authorized by Sony and Mitsubishi? |
| Sony, you must sell the product lines you wish to service otherwise they will not authorize you. MGA, attend their training seminars to become certified by them in servicing their product lines. |
| QUESTION NO. P86-11: How can I get a smps to operate without connecting it to the computer? |
| Occasionally I am given a power supply module from a computer to troubleshoot or confirm proper operation.Many of these do not work disconnected without a load. They simply just sit there. With a few simple items I built a test "jig". These supplies usually have one or two +5v sources, a -12v, and a +12v source. Simply place several 12v automotive bulbs and several common 6v bulbs on a small wooden block for stability. Use sockets or any way to mount them. On each bulb, attach two "clip leads"(+ and ground). You can color code them if wanted. Simply clip the 12v and 6v leads to proper outputs of power supply and you have a good "dummy load" to operate it separated from its computer. Gives a good visual indication, too. |
| QUESTION NO. P728-4: I am trying to learn how to repair newer surface mount circuit boards. However, I am having a really difficult time identifying and defining values of surface mount components. Can you suggest where I could easily find (or if you could post on a web page?) the codes for surface mount resistors, capacitors, etc? |
| When you find this information please inform the rest of us techs. Seems that the Manufacturers have not yet defined a hard standard for the indentification of most smd devices, other than device and house identification nunbers. Some have small color codes or indicator numbers, but trying to get a comprehensive answer about identification is almost nil. |
| QUESTION NO. P610-7: What is the "Right Hand Rule" in circuit analysis? |
| To determine the direction of magnetic flux created by the flow of electric current through a conductor imagine grasping the conductor in your right hand with the thumb pointed in the direction of current flow. Then your curled fingers are the direction of the magnetic flux. |
| Another version: The "Right Hand Rule" applies to checking out a live circuit with your right hand in your pocket to keep from unknowingly creating a ground loop which could ruin your day! |
| QUESTION NO. P36-8: Please advise me the method of repairing the pads on the PCB which is only partially lifted. I suppose I have to use a glue? |
| ANSWER 1: After many years working with micro-miniature repair, the easiest and correct fix is to clean the lifted pad and scrape away any conformal coating from the pad and board. Mix a small amount of good quality (ie..3M) epoxy. Apply the epoxy to both the board and the underside of the pad. The pad must be clamped or weighted down to the board and allowed to dry for 24 hours or put in a shop oven @ 150 for about 1 hour. Always remember to us a slippery plastic, such as coffee can lids, between the clamp and the board or the clamp becomes a part of the circuit card. |
| ANSWER 2: I have encountered this problem numerous times (pads lifting) while removing Bake-a-Lite from Videocypher modules with a heat gun. As heat was the culprit causing the pad to loosen, you'll be hard pressed to find a glue to rebond the pad. You'll find it easier to solder a small guage single strand of wire to the trace itself by scratching coating off of the trace and tinning the trace, then take other end of wire through the eyelet hole and solder the component leg directly to this wire. |
QUESTION No. P812-1: I need a contact number for SANSUI ELECTRONICS CORP. |
Sansui Electronics was absorbed by the Semi-Tech conglomerate, which includes Akai, as well as Singer and Pfaff. You can request information regarding Sansui via the Semi-Tech website at http://www.semitechglobal.com/stg!05-01.html. |
QUESTION No. P63-4: Does anybody know how to make ring tester for flybacks? |
For everything you need to know about testing flybacks, I suggest you go here. I have built and used the active circuit tester, and it is neat. Glue problems: |
| The AnaTek Data Direct has detailed information on flyback testing and test equipment.. Data Direct contains most of Sam Goldwasser's writings on how to repair nearly everything electronic as well as these www pages and the postings to ELREPAIR-L electronic repair discussion group. A powerful search engine is included for searching the CD on any topic. See details of the AnaTek Data Direct CD. |
QUESTION No. P318-3: Can anyone refresh my memory on the rules regarding the use of two polorized capacitors for use when you do not have the right value (1000Uf, 300 V)? |
You will need 2, 2000uF electrolytic capacitors rated at least at 150V each. The rule is double the required capacitance, divide voltage by half. Since you will be wiring them in series, each capacitor will see 1/2 the applied voltage. But because you are in series, capacitance will be divided by half, thats why you have to double it. + - + - - + - + Note: Make sure your capacitors are the same capacitance. If you use caps that are from 2 different manufactures or the capacitance are quite different, the voltages will note divide equally on each cap, possibly exceeding the 1/2 rule for voltage. If that happens, you will learn a lesson the hard way, like I did, and have the capacitors heat-up, bulge and explode! CAUTION from another tech: There is only one way to connect 2 polarized capacitors in series. The (-) of one cap must be connected to the (+) of the other cap to maintain proper polarity in both. |
QUESTION No. P110-4:Looking for plans to assemble a device I used to know as an "Octopus". It was used to troubleshoot electronic components unpowered and still mounted on the circuit board. It is supposed to be relatively inexpensive to build and is used in conjunction with an oscilloscope. |
To build an "octopus" you will need a transformer with a 6.3V secondary, a 6' BNC to BNC coax cable, 2 test leads, and a 330 ohm 1/2 watt resistor. Cut the coax in half, strip and dress ends. Connect one test lead and one coax inner conductor to one side of the transformer secondary. This coax goes to scope X input. Connect other coax inner conductor and one end of resistor to the other side of transformer secondary. This coax goes to scope Y input. Finally connect loose end of resistor to other test lead and one or both coax shields. Connect power to transformer primary. Set scope to X-Y display, 5V per div, dc input coupling. |
QUESTION No. P1112-1" RCA ctc187bj powers up with video and second audio only. The video has what appears to be four (4) pictures across the screen. They are some what torn horizontally but visible and appear to be the right one third of the picture. I have scoped u1001 and the detected video at pin 48 is ok the burst at 49 is ok but the video at pins 36-37-38 all have the classic shape and size except they also have about a 600KC square wave in the synch area (below video level). The control pulses into u3101 pin 39 appear good and on time. |
ANSWER 1: Check the EPROM that is used in these and other RCA/GE sets. |
ANSWER 2: Enter service mode and adjust horz. freq. to value 11 then resolder bad grounds that caused it to go bad. |
QUESTION No. P108-1: Where can I find some pager repair and setup training schools? Also some sources for procuring pager related service and process equipment, including parts like crystals, replacement boards, LCD bonders, vibrators, beepers, etc. |
Try Motorola National Service Training. They offer repair classes on all of their pagers. They can also set up an account to order replacement parts for their pagers. They are located in Boynton Beach Florida. |
QUESTION No. P827-1: I need a method of reflowing the solder on surface mount components to repair possible or known poor connections. Most usually on SMT micro connectors inside camcorders, and sometimes fine pitch quad pack IC's. I have used a needle sized iron in the past, but the time to do > 50 pins is excessive. What is the industry standard at this point in time? Remember the access inside a camcorder is sometimes limited. |
The technique I use for reflowing quad pack IC`s is to use a larger tip to solder all the pins together, this sounds extreme but you can then use desolder wick to remove the solder from above and between the pins leaving the solder underneath. |
| A much easier and faster (and more reliable) way to reflow or solder smt chips is to apply a generous portion of paste flux to the board/chip/pins where you're going to solder, hold the board at about a 45 degree angle, and with your soldering iron tip tinned and heavy with extra solder, start at the top and just drag the iron down slowly. The flux will prevent solder from sticking between pins. I have successfully reflowed every chip on a Pentium 3 processor (slot 1 type) this way in about 5 minutes. |
QUESTION No. P89-2:Where we could to buy manuals and schematics of electronical equipments. FROM WEBMASTER: This question comes from a Russian technician - Anyone know sources in Eastern Europe? |
I do not know any Eastern Europe but a company called Logitron in the United Kingdom has an extensive list of schematics for monitors and some system units, especially IBM. Their international sales number is +44 181 9877007. |
QUESTION P32696-2: Does any know where to get information on A+ Certification or Computing Technology Industry Association who certify the competency of service techicians in the computer industry? |
A+ Cert. Info - (800)77-MICRO Check with your local trade schools or colleges offering electronics. Ours offers cet certification courses. Cet also as a sat-link course I believe. |
QUESTION No. 21596-10: I need the pinouts for the STK6982B. |
STK6982B=ECG1736: 1: VCC, 2: MTR A Common, 3: Diode, 4:MTR A, 5: A Input, 6: MTR A(overscored), 7: A(overscored) input, 8: REF1, 9: V-REF, 10: GND, 11: V-REF, 12: RE2, 13: MTR B, 14: B Input, 15: MTR B(overscored), 16: B(overscored) input, 17: MTR B Common, 18: Pause |
QUESTION: How well do service contracts work out? |
I've been doing service contracts for 20 years and the key is "SELL LOTS OF THEM". Any one contract can eat your shorts. But, for every bad one there are several good ones and you "MUST" take the bad with the good or your rep will suffer. The price I charge for a one year contract is aProximatly 10% of the original purchase price. |
