Tube amp FAQ: * http://www.eden.com/~keen/tubeampfaq/tube_amp.htm Sites with tube amp design, troubleshooting, info, links: (From: Duncan Munro (firstname.lastname@example.org)). * http://www.duncanamps.simplenet.com/ * http://www.triodeel.com (From: Jan B. Jensen (email@example.com)). * http://www.foundmark.com/ComJute/RealMcCoy.html * http://venus.aros.net/~tboy/ampage/schems/twdpwr100.gif * http://mirinae.yonsei.ac.kr/~hscheon/tube/ * http://nanaimo.ark.com/~pat/index.htm * http://www.eden.com/~keen/ * http://www2.aros.net/~koda/htac/ * http://www.geocities.com/TimesSquare/1965/music_etc.html * http://www.phy.ohiou.edu/~cigna/amps/
These hybrids which include both a TV and VCR (and sometimes other stuff as well) seem to combine the worst of all possibilities. Although, in principle, the idea of a combination TV/VCR sounds good - no cabling to worry about, ease of use, compatibility assured, the result may be less than meets the eye. While TV/VCR combo units do include both a TV screen and a VCR transport, very often there is only a single shared tuner so that viewing and recording of different programs is not possible unless one is from an external baseband video source (assuming there is a suitable input jack) like - you guessed it - a VCR or laserdisc player. If either the TV or VCR poops out and needs repair, the entire unit may be unusable either because of shared circuitry or because the whole thing is in the shop. Construction quality tends to be shoddy and some designs are poor to begin with. Finally, as if this is not enough, servicing is difficult and painful because everything is crammed into a single compact (at least that is a good feature!) unit. Refer to the appropriate documents for your particular problems: * TVs - "Notes on the Troubleshooting and Repair of Television Sets". * VCRs - "Notes on the Troubleshooting and Repair of Video Cassette Recorders". * Power supplies - "Notes on the Troubleshooting and Repair of Audio Equipment and Other Miscellaneous Stuff".
These combine a stereo receiver and a single or dual cassette deck, and/or a CD player or changer, and a pair of detachable speakers, into a single unit. Most are fairly portable but larger boomboxes and compact stereos may require a forklift to move any great distance. While the individual subsystems - CD player for example - are usually relatively self contained electrically except for a common power supply, mechanically, everything tends to be jumbled together - even on units that have an outward appearance of separate components. Both cassette transports are usually driven from a single motor. Getting at the CD player may require removal of both cassette decks, audio amplifier, and power supply. Working on these is not fun. As usual, take careful notes as you disassemble the unit and expect it to require some time just to get to what you are after. Be especially careful when removing and replacing the individual modules if printed flex cables are used for interconnections. Refer to the relevant sections on cassette transports, loudspeakers, and power supplies for problems with these units. Refer to the document: "Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives" for CD specific problems. Since these do get abused - bumped, dropped, dunked, etc., bad connections, and other damage is very common. See the sections: "General intermittent or erratic behavior" as well as "Noisy or intermittent switches and controls".
Here is a description of the pain involved in attempting to get at the CD player part of a Garrard boombox. Sadly, this is all too typical of 'Getto Blaster' construction. (From: BELJAN E (firstname.lastname@example.org)). I managed to get the whole Garrard mess disassembled (this thing is a major pain to service). The CD mechanism is removable, but just try it. This boombox has all sorts of modules: main board, display, cassette, radio, power supply, and CD are all separate. The problem is the way it is designed you simply cannot reach all the connectors to get the CD player out. If I could get the CD player out, I could disassemble it and find the solution. By the way, voltage to CD section appears OK. I would not have been able to find loose connections had there been any. I put it back together, CD still dead, everything else still works. It is convenient to service only if you intend on replacing the entire mechanisms (possibly Garrard's motive?). If I really needed to, I could simply detach the CD mechanism and replace it. I wouldn't bother. I see they now have Garrard Boombox with Dual CD players, and one with all sorts of features, one with detachable speakers and so on. This is a mystery, with the voltages OK, it would seem that there would be a loose connection, but none are visible (remember I cannot get the whole thing out). I say this thing is a pain to service, here is why: 1. You must have an 8 inch long thin phillips screwdriver to disassemble it. 2. You must remove the cassette player to reach the Display. 3. You must remove the display to reach the switches. 4. You must remove the switches to reach the CD mechanism. An interesting note: the display modules are connected to the CD mech, along with the headphone module, they work fine. 5. you must unscrew the CD player from behind, then attempt to slide it forward, while it is connected to the main board from behind with white push on connectors. You get it halfway out, careful now, you don't want to damage the Cassette deck, which is connected somewhere out of visibility. 6. Once you slide it forward, you must try to loosen the slide on connectors without dropping the whole mechanism on the main board. (you need 6 hands and screwdrivers to try to do this. 7. On top of all that, the Whole Front of the unit is hanging there, connected also out of site This unit is incredible. Truly incredible. It is easy to replace whole components, but servicing?
In the old days, this was due to the failure of easily replaceable and widely available miniature incandescent lamps. Even today, may displays are not LEDs as you might think but LCDs with backlighting provided by - you guessed it - incandescent lamps. Unfortunately, they are rarely easily replaceable and or as widely available. This will be particularly likely if the display color is anything but the most common for LEDs - red. You might find green LEDs but will not likely find orange and certainly not blue or purple. LEDs would not be orange because the additional cost of orange LEDs would not translate into increased sales of boomboxes (or whatever). Blue LEDs are very expensive and purple ones do not exist. The bulbs are replaceable. Getting at them may be easy or require entirely disassembling the unit. Soldering may be required as the manufacturer saved a nickel by not providing a socket. They may be tiny and special - try places like MCM Electronics for replacements. If they are really red LEDs or vacuum fluorescent displays, then the most likely problem is a bad connection or other physical damage.
So 95.7 MHz comes in a 100.1 MHz on the dial. Don't touch any of the trimmers on the tuning capacitor! They didn't magically change their settings. Just move the pointer on the dial cord to match a known centrally located station. If it is glued, you may have to carefully break the bond between the pointer and the dial cord. Then put a drop of household cement to fix its position when you are satisfied with the adjustment. Only if the ends of the dial are way off frequency should you consider anything beyond this mechanical fix. Caution: Be careful! Should you accidentally cut the dial cord or have it pop off of the pulleys, you will have a much bigger job ahead of you. In this unfortunate circumstance, see the section: "Repairing a broken dial cord or tuning gang wire".
With age, use, or through some mishap, it is inevitable: your analog dial no longer works because the string that runs between the tuning knob, variable capacitor, and dial indicator has broken. How does one repair it? The simple answer is: very carefully! :-) These are a royal pain - especially if you do not know the original routing. In this case, some of it is going to be by trial and error. Some of my learned-the-hard-way tips: 1. Major electronics distributors will actually be able to supply dial cord material without making too much of a face though they may have to go into a dusty old bin to locate it! 2. Start at the variable capacitor pulley. Tie your favorite knot and secure it with some semi-flexible adhesive like Duco Cement(tm) or windshield sealer. 3. Route the cord around the appropriate idlers and the tuning knob shaft. 4. As a default, 3 turns on the tuning knob shaft seems to be common. If there isn't enough space for 3 turns, use 2 turns. If it slips with 3 turns, use 4 turns. 5. If in doubt about the direction, determine which way it will end up turning the variable capacitor. Clockwise rotation of the tuning knob should increase the channel frequency by decreasing the capacitance - plates separating. 6. Use bits of electrical tape or putty to keep the cord from popping off of the idlers, etc., until you have it firmly attached to the spring on the other side of the variable capacitor pulley. 7. Once you are happy with the routing, pull it tight enough to stretch the tensioning spring about half-way. With the cord held in place with your finger, confirm free and smooth movement throughout the entire tuning range. 8. Tie the cord off and seal it as in (1) above. 9. Install the dial pointer - it usually just clips on. Tune a known station and slide the pointer along until it lines up with the correct frequency. Use a dab of sealer to keep it from wandering off. Congratulations! You are done. Hopefully, only 3 or 4 iterations were needed. Now, if you need to do this again, it will be easier! And, your supply of tuning cord will probably last centuries. One more gotcha: Don't attempt to solder circuitry near a dial cord - get your iron near it and the stuff often used melts instantly - much fun! Push it out of the way or shield it with something.
There are two types of problems with hand held remote controls: they have legs of their own and they get abused or forgotten. I cannot help you with walking remotes. Where response is intermittent or the reliable operating distance is reduced, first check the batteries and battery contacts. If some buttons are intermittent or dead, than the most likely cause is dirty or worn contacts under the rubber buttons or on the circuit board. If there is no response to any functions by the TV or VCR, verify that any mode switches are set correctly (on both the remote and the TV or VCR). Unplug the TV or VCR for 30 seconds (not just power off, unplug). This sometimes resets a microcontroller that may have been confused by a power surge. Confirm that the remote has not accidentally been set to an incorrect mode (VCR instead of TV, for example). If it a universal type, it may have lost its programming - reset it. Make sure you are using the proper remote if have multiple similar models. Test the remote with an IR detector. An IR detector card can be purchased for about $6. Alternatively, construct the IR detector circuit described in the companion document: "Notes on the Troubleshooting and Repair of Hand Held Remote Controls". If the remote is putting out an IR signal, then the remote or the TV or VCR may have forgotten its settings or the problem may be in the TV or VCR and not the hand unit. The following is just a summary - more detailed information is available in the companion document: "Notes on the Troubleshooting and Repair of Hand Held Remote Controls". Problems with remote hand units: All except (1) and (2) require disassembly - there may be a screw or two and then the case will simply 'crack' in half by gently prying with a knife or screwdriver. Look for hidden snap interlocks. 1. Dead batteries - solution obvious. 2. Corroded battery contacts, Thoroughly remove chemical deposits. Clean contacts with pencil eraser and/or sandpaper or nailfile. 3. Broken connections often between battery contacts and circuit board, possibly on the circuit board - resolder. 4. Bad resonator or crystal - replace, but diagnosing this without an oscilloscope may be tough. Broken connections on resonator legs are common. 5. Dirt/spills/gunk preventing keys from operating reliably. Disassemble and wash rubber membrane and circuit board with water and mild detergent and/or then alcohol - dry completely. 6. Worn or corroded contact pads on circuit board. Clean and then use conductive Epoxy or paint or metal foil to restore. 7. Worn or dirty pads on rubber keypad. Clean. If worn, use conductive paint or metal foil to restore. 8. Cracked circuit board - can usually be repaired as these are usually single sided with big traces. Scrape off insulating coating and jumper breaks with fine wire and solder. 9. Bad LED. If IR tester shows no output, remove LED and power it from a 9V battery in series with a 500 ohm resistor. If still no output, replace with readily available high power IR LED. Otherwise, check driver circuits. 10. Bad IC - if it is a custom chip, forget it! Failure of the IC is usually quite unlikely. (The following is from Duane P Mantick:) An awful lot of IR remotes use IC's from the same or similar series. A common series comes from NEC and is the uPD1986C which, incidentally is called out in the NTE replacements book as an NTE1758. A lot of these chips are cheap and not too difficult to find, and are made in easy-to-work-with 14 or 16 pin DIP packages. Unless you have no soldering or desoldering skills, replacement isn't difficult. There are a large variety of universal remotes available from $10-$100. For general TV/VCR/cable use, the $10 variety are fine. However, the preprogrammed variety will not provide special functions like programming of a TV or VCR. Don't even think about going to the original manufacturer - they will charge an arm and a leg (or more). However, places like MCM Electronics do stock a variety of original remotes - prices range from $9 - $143 (Wow $143, for just a stupid remote! It doesn't even have high definition sound or anything exotic). The average price is around $40.
Most common are moisture problems followed by physical damage: Very often, a little overzealous cleaning results in moisture trapped inside a not quite perfectly sealed membrane keypad or touchpanel. First, of course, dry off the exterior as best you can. Any moisture that seeped inside may be difficult to remove without surgery - which is definitely not something you want to undertake as the long term reliability will be compromised. I would recommend waiting a while - a week may be required - for it to totally dry out. You could also try confirming across the touchpad contacts with an ohmmeter that there is still low resistance (even 10s of K ohms may look like a button press). It is nearly impossible to speed up this process without subjecting the device to conditions that may harm the device - heat and/or vacuum. You possibly try something like isopropyl alcohol in the hope that it will displace the water and dry quickly. I do not know if this will be safe in every situation, however. Of course, it is also possible that are other problems but I have seen these things take a very long time to dry out. However, significant damage - a membrane type touchpad is punctured - may require replacement unless you can repair the internal wiring. The connections are usually made with flex-cables which are difficult or impossible to repair. See the section: "Repairing flexible printed cables". Damage to any membrane buttons may result in stuck buttons or improper operation of other buttons.
It seems that more and more consumer devices from pocket cameras to laptop computers are being built with miniature multiconductor flexible printed cables. Very often one or more traces to develop hairline cracks due to repeated flexing. In addition, damage from moving circuit boards and modules during servicing is all to common. Needless to say, repairing any kind of flex cable is a real pain! Caution: many devices like calculators have printed cables that use a material that will not take solder and are glued rather than soldered at their ends - the logic board and LCD panel, for example. Repair of problems with the cables is virtually impossible. Take great care when working inside of devices with this sort of cabling to prevent damage to the cables or their termination. With types like these in particular where soldering is not possible at all, the use of conductive paint, conductive Epoxy, or the stuff in a windshield defrost heater repair kit are worth trying. For the metallic conductor types, I have succeeded by carefully scraping the plastic off with an Xacto knife and then soldering fine wire (#30 gauge wire wrap for example) to the traces. This presumes that the conductors on your cable will even take solder. I then cover up the joints with a flexible sealer for electrical and mechanical protection. However, you need to make sure that the wire you use can be flexed or that the joint is set up in such a way that the wire does not flex much - else you will just end up with broken wires pretty quickly. Soldering from end point to end point if possible may be preferable. Even going to only one endpoint would reduce the risk of immediate damage and reliability problems in the future. With multiple traces broken or damaged, you are probably better off replacing the cable entirely. (From: Steinar Botten (email@example.com)). I just fixed an electronic kitchen scale where the glued-on flex cable had begun to come loose from the LCD display, causing some of the segments to grow faint and disappear, while others showed when they shouldn't. In my first attempts I used conductive paint, but I couldn't get the viscosity right so that the paint didn't spread and short-circuit some of the connections. So I removed and discarded the flex cable and cleaned the tracks on the PCB where the cable had been attached. I searched through my collection of IC sockets and found one type with "fork-type" contact springs that could be removed from the socket and that fit snugly over the glass edge of the display. The spacing of the contact points of the display left just enough room for insulation (I used linen thread because the subsequent soldering would have melted plastic tape) between the contact springs. After having fixed the display back on the PCB with double-sided tape I soldered fine copper wire between the springs and the PCB. And voila, the display was OK again. Some ASCII art might make things clearer, here is a side view of the LCD display: ___ ! ! ! ! ! ! ! ! ! contact !_! ! side --> ! ! !! !! !!_!! !___! <-- contact spring from IC socket ! ! Obviously, this probably wouldn't work on a pocket calculator because of the size of the contact springs.
(From: Ken Bouchard (firstname.lastname@example.org)). These are the leading cause of problems for me! I repair camcorders for a living, and all too often have seen these flex cables fall off the PCB, or are so delicate in construction that they fall away from the PCB. In many cases during repair stage, I often touch up the soldering with a low heat iron, while pressing down on the soldered to PCB area of the cable, with a flat plastic blade, enough to re-flow the connection. Then I take and apply some general purpose glue around the cable to get it to adhere better to the PCB and prevent tearing. Of course the consumer never should encounter a problem unless the camcorder is dropped, and the case splits open and rips the connectors away from the PCB. Sony is infamous for having connectors fall off the boards. Many brands of camcorders are infamous for having connectors that mate 2 boards together break away from the PCB. It is a very bad situation because the boards they work with are very expensive to replace. For the cost of a simple piece of flex cable and 2 insertion force sockets, it is amazing they are cheap and choose to mate the boards together directly, knowing that failure is just around the corner! Most commonly the CCD board or camera assembly is mated to the video (main) PCB in this fashion and it is very sad when they break due to stress. This is one reason that the consumer should never ever attempt to repair delicate items like this. The best you can hope for in dealing with these is to never attempt to repair the flex cable by soldering to it, etc. That is asking for future problems at best... Don't 'tin' the ends of the cable either, you simply melt and distort it so that it will no longer get a good connection into the socket. Only clean it possibly with denatured alcohol if needed - otherwise replace it. Also do not stress them, you soon discover how easily they rip!
Remember that first (or last) digital watch you took apart? Remember how a little piece of rubber fell on the shag carpet and you thought: "What the heck, that can't be anything important". Remember how the watch's display never worked again? Well, you lost the connector that linked the LCD panel to the logic board. Elastomer or 'zebra stripe' connectors are used to attach LCD panels to the logic board and interconnect multiple boards on digital watches, calculators, pocket computers, and many other modern gizmos. It seems as if every cheap and many not so cheap gadgets now uses this connector technology. They can shift position, become dirty, and lose pressure due to warpage or damage to the plastic retainers. Very often, a weak display or missing segments can be traced to a problem with these 'zebra stripe' connectors. Equally often, disassembling, cleaning all parts with alcohol, drying, and reassembling will return the device to (better than) new condition. When installing, make sure the striped edges are against the circuit traces if there is any ambiguity. Of course, it isn't that the zebra stripe shifts position a small amount - by its nature this should not matter. However, if the display shifts with respect to the circuit board contacts or the zebra stripe material becomes twisted or angled, poor and/or erratic connections will result. (From: Spehro Pefhany (email@example.com)). These are conductive elastomer connectors made from alternating layers of conductive (carbon filled) and insulating silicone rubber. There are also lower resistance versions with embedded wires, but they are not used for LCD displays because the series resistance doesn't matter for LCD's. Alignment to the PCB is critical as is even pressure, so they tend to be used only in high volume applications where a metal stamping or plastic molding is used to hold all the parts in place.
So you want to use your old car stereo as a boombox but don't have the connection information. Here is what I would do: Locate the power - there will be a +12 switched and possibly a +12 unswitched for channel memory. At least one may be obvious if has an in-line fuse. Use an ohmmeter if necessary. Once you have found the power connections, power it from your 12 V power supply. Keep the volume way down and use the balance and fader controls to identify the speaker connections. There will be either 2 pairs of wires or more likely 4 pairs for front and rear speakers.
(From: Raymond Carlsen (firstname.lastname@example.org)). I recently had to repair a power supply for a camcorder. It was dropped. Parts of the case were broken, and the circuit board inside was cracked. Board repair was easy. I glued the PC back together with superglue and soldered across the broken traces with jumper wires. The plastic case presented me with more of a challenge. Two little "ears" held the front end cap on the unit with small screws. The ears were broken into several pieces and could be heard rattling around inside the case. I could glue them back together, but the results have, in the past, been unreliable at best. I decided to try and reinforce the plastic. I often melt solid hookup wire across a break (on the inside, where it doesn't show) with a soldering iron to strengthen a glued area, but these tabs were so small, any heat would warp them and the case would not fit back together. What to do? I noticed once that when Superglue gets on ordinary notebook paper, it gets hard as a rock. It is difficult to tear, but is flexible enough to bend a little without breaking. Since one side of the little plastic ears were essentially flat, I superglued a strip of paper on each ear. The glue partially melted the plastic and made a good strong bond. After the glue set up, I trimmed the edges with an Xacto knife and poked holes in the paper for the mounting screws. The finished repair is stronger than the original product. The paper reinforcement is thin enough that there was no problem fitting the front back on the case.
Electronic equipment is happiest if kept in the same type of environment that humans like - moderate temperatures, low humidity. What if you are forced to store equipment for months or longer in a non-environmentally controlled space like a public storage facility? Recommendations: 1. Find some long lost relatives who will store the electronics for you in a heated space. If this is not possible: 2. Seal each piece of equipment in a thick plastic bag along with a pack of dessicant to keep it dry (that silica gel stuff you always throw away). This will preferably be in the original packing box (and include all cables, accessories, and manuals, so they won't get lost.) Moisture is more of a problem than the absolute temperature (within reason) or temperature fluctuations. Therefore, avoiding the totally damp and dingy dungeon of a medieval castle is definitely desirable.
When you purchase a commercial piece of equipment, it is assumed that the construction has been done properly. This may not always be the case but it is more likely when a million of something is manufactured than a hand soldered kit possibly assembled by someone who barely knew which end of the soldering iron to hold! I picked up a Heathkit DMM at a garage sale for next to nothing that had apparently never been quite completed. The problem turned out to be a defective rectifier in the power supply. However, everything else including the soldering was perfect. For kits, this may be the exception :-(. The original owner must have given up when the DMM didn't power up properly - and had no DMM to debug it with! (Portions from: email@example.com (Mike McCarty) 1. Look for improperly soldered joints. Kits often are soldered by people with, shall we say, less than completely optimal soldering skills. I have looked at kits I assembled when I was a teenager, and can't believe the joints were really that bad. 2. Clean any switches or other moving contacts with some good TV tuner cleaner. 3. Vacuum out any dust which may have accumulated. I prefer that to using compressed air, but you may use that also; be careful of compressed air which may come out with a high static charge. 4. Reseat socketed components and any boards with edge connectors. If the contacts look oxidized, clean them with a soft pencil eraser and/or contact cleaner. Look for loose spade connectors as well. 5. Check for loose screws or other fasteners and tighten if necessary. 6. Jiggle wires and look for corrosion/fatigued wires especially where flat ribbon type cables are used 7. Where something is more than 10 years old (in particular), it may be a good idea to check and/or just replace any electrolytic capacitors which may be drying out. 8. Replace any primary batteries after thoroughly cleaning the battery contacts. Depending on age and previous use types may also be bad as well. Discharged lead-acid types more than a year or two old are likely hopeless. However, I have found some NiCds that were quite old and perfectly fine. 9. Finally, if the equipment had possibly never been operational (i.e., you found the cover still in its protective plastic bag!), check ALL components for proper location and direction before applying power. Of course, it may already be too late if there was a part installed incorrectly and the original owner attempted to power it up.
I usually start with soap and water or mild detergent. If this does not work, rubbing or 91% medicinal alcohol, 'Windex', and then, WD40 are tried. All of these are usually safe for plastics though some paints or printing may be affected - test on an inconspicuous area first. Scouring powder and/or sandpaper is only used as a last resort! :-) However, in some cases, where there is serious discoloration due to heat and ozone, these may prove somewhat effective... One or more of the following will probably work even for tough tobacco smoke/tar buildup: (From: Terry DeWick (firstname.lastname@example.org)). I have found plain household ammonia works well especially since it is cheap, if not available I use '409' or 'Fantastic' cleaners. (From: Ralph Wade Phillips (email@example.com)). 'Scrubbing Bubbles' bathroom cleaner (Dow is the brand I use) works better than anything else I've found yet, besides chucking the case. Be sure to follow with a decent Windex-like cleaner - the residue from the Dow cleaner will cause you to gasp every so often for the next six months! (From: Joe (firstname.lastname@example.org)). Go to SAM'S and get a jug of 'ENTNT'. Mix it in a spray bottle with water (I like about one part ENTNT to four parts water) and enjoy watching the nasty brown yuck drip off the monitor. Finish the job with windex to remove the residue from the ENTNT. The ENTNT is safe on plastic, but test it on painted surfaces first.
(From: Jim Leone (email@example.com)). I have two words (no they are not plastics --- sam): Resistor Glue. A lot of today's electronics manufacturers, before the printed circuit board goes through the flow solder machine, use a certain type of glue to hold down large components like heatsinks, electrolytic capacitors, and resistors. After 2 to 3+ years of life, bonded to a high temperature component, this glue turns conductive!!!!!!! One blatant example of this is the Viewsonic (however many other manufacturers use the same type of stuff) 4e Model 7033 computer monitor where the 86VDC main rectifier on the switching supply has it's pins coated with this 'Resistor Glue'. When the monitor was new the glue has a tan color and kind of feels like really dried up chewing gum. You know, the kind that has been under a desk for 1 year. After about 2 years, the color has changed to a darker brown; it could be almond to dark walnut colored. Now you should be able to easily remove it by scraping it away with an Xacto knife, and it will crumble away. However, in equipment left on 24 hours a day in moderate to high heat environments this glue takes on a more carbon hue. Typical units have holes burned right through the circuit board and others are left with carbon scarred 'divits' on the board that must be gouged out to keep the supply from arcing across. On one hand, an optimist might say that this is a result of engineers who's goal was to get the product out before the deadline at the end of the month. But on the other hand, a pessimist could say that this is a result of blatant planned obsolescenceGo to [Next] segment
Go to [Table 'O Contents]