Our online manuals are available here in PDF format free for downloading. If you have any further questions regarding downloading of Magnetek's Product Manuals, please call 1.800.288.8178. I just got it out and it is a Magna-Tek TU-740-2. Average charge rate 4 amps. Looks like I will be ordering a Boondocker.
Repairing Magnatek RV Power ConverterRepairing the MagnatekPower ConverterNote: This unit was in my Sierra30 foot trailerWhen spring came and I prepared to get my RV all un-winterized and ready to take out, Idiscovered that my trailer battery was nearly dead. Since it was new from just the yearbefore, I thought I wasnt getting very good mileage on batteries but I thought Iwould do some other checking before indicting the battery as defective. First, doing somevarious voltage checks, I found that I had good 12 volts DC to my interior lights and tothe voltage monitor on the control panel. That voltage wascoming from the power converter 12 volt supply (although not from the converter's batterycharging section).Checking the cigarette lighter socket, it only showed 5 volts and I determined thatthis was coming directly from the battery which was, by then, in a near dischargedcondition. Although the trailer had been plugged in all winter, the battery had notreceived any charge since the battery charge feature in the power converter had failed inmy Magnatek Power Converter, and I didnt know when that had happened. The batterywas OK, the Magnatek higher current 12 volt section was OK but the battery charger sectionof the converter was not OK.Checking at the Magnatek panel in the bathroom, I found no voltage between point C(which was the positive side from the battery) and point D (which was the negative sidefrom the battery).
Now I knew where I had to concentrate my attention. NOTE:Points C and D are actually labeled as such on the unit.At this point I spent several hours combing the Internet in search of a schematic forthe Magnatek converter. Totally without success. I read jillions of messagesfrom RVers, several asking for the same thing I sought. I wanted any kind ofinformation, particularly a schematic, for this unit.
I even contacted some of thesepeople to ask if they had been successful in the search.Nope.nada.nothing. No such luck.I found a telephone number for the factory which built the unit and even tried to callfor info. Human help was available for warranty work but my unit was several yearsout of warranty. I was out of luck.I needed that schematic and since it was unavailable, it looked like I would have togenerate one myself.
If youve ever tried to do this it is akin to somewherebetween trying to write down a cake recipe from only having the completed cake in front ofyou and unscrambling an egg. Not much fun, especially if the parts have non-standardmarkings or no markings at all. Like my converter.I was ultimately successful and the schematic I have included is close enough, if notan exact rendering, of what is found in the Magnatek power converter. I hope ithelps others as it helped me. Now, with schematic in hand, I returned to the project ofrepairing my converter.PIC #1: The circuit schematic is actually in two parts. The first part,shown above, is the main power supply part of the converter.
Thanks to a readernamed Baldy in California, you'll be able to see the pictures better than they originallywere displayed. Baldy took my original pictures, which were upside down andsideways, and corrected them for me. Thanks Baldy.PIC #2: The schematic above is the battery charger part of the powerconverter. It will charge the RV battery but then automatically taper down toa trickle charge so as not to destroy your expensive battery.PIC #3: I included this picture but I'm not absolutely sure of its totalaccuracy. I drew this out several times and I think this was the final version.Don't hold me to it, however, and if there is a discrepancy between the schematicand the underside of the PC board, you should believe the schematic first.UPDATE NOTE: Since publishing thisoriginal article someone sent me the actual schematics on a Magnatek RV power supply.CAUTION: When you decide to work on your power converter, besure you unplug your trailers power cable from the 117 volt AC mains.Once that is done you can remove the screws holding the panel/cover onto theconverter. This will expose the transformer, diodes, solenoid, fan and batterycharge board.
This solenoid is energized whenever the trailer is plugged intoexternal AC power and it allows the converter to send charging voltage to the trailerbattery. Magnatek chose to use a solenoid to activate a switch to perform thisfunction rather than use a relay.
I dont know.The following are steps required to remove all connections so you can pull the wholepower converter out to work on it:1. Remove the 4 hex-head screws which hold the front board.2. Remove the 2 hex-head screws holding the other board.3. Remove the 12 volt wiring to the 12 v. Distribution board the white andred wires have screws, the blue (12v) wire is attached with a screw and nut.4. Open the cover to the 117v AC circuit breakers.(You did disconnect the 117v AC didn't you?)5. Remove the white wire which goes to the left side vertical screw strip.6.
Remove the black wire coming from the far right-hand circuit breaker.7. Carefully feed the 2 AC and 3 DC wires from the top box so they are inside thebottom power supply box.
Now you can remove the power converter pieces.8. With the power converter box on the workbench, remove 2 hex-head screwsholding the nylon posts which are holding the battery charger circuit board.9. NOTE: With the power converter box on the workbench, the top cover canbe removed with 4 hex-head screws. This allows full access to the inside components.The next step is to remove the board containing several electronic parts includingresistors, silicon controlled rectifier, zener diode and a capacitor.
This board, onmy unit, stood vertically and was attached to the right-hand wall of the supply.NOTE: Do NOT attempt to pop the board off the nylon posts where it ismounted. It will not come off and attempting to pop it loose will result in a crackedboard, which is made of rather fragile phenolic material. Breaking that board canseparate traces on the printed circuit board and you will have additional problems.The board can be removed but only after the whole box, holding the supply, is removed. (Aword to the wise. Ask me how I know this.
No.never mind.)It is now that you must use your electronic trouble-shooting skills to determine whichcomponent or components might be causing your problems. That is rather difficult forme to tell you what might be causing your converter to fail but, hopefully, thisinformation and the schematic provided will allow you to find it.My problem turned out to be the large rectangular resistor mounted with a pop rivet tothe back panel of the box. The value was obscured on mine but an ohmmeter check showed thevalue to be more than a megohm which was much, much too high.
I would guess that itstrue value should have been less than an ohm but at a high power rating, perhaps 50 100 watts. It was here that I had to do some guessing. Since this resistor islocated in the line providing charging current to the trailer battery, my guess is thatits function is to drop the load a bit when first connected to a battery which is totallydischarged. A fully discharged battery would place a tremendous temporary currentload on the power supply components and this resistor helps to protect things duringthat initial surge.After the repair was complete, I did some checking on the converter to see just howmuch current was provided to a battery for charging and to see whether the higher currentstayed up at the high level or if it tapered off to a trickle charge as this type ofcircuit should do. With a 0-3 amp meter in series with the battery charging line,and using no extra resistance in the line (the big white rectangular resistor was shortedto make zero ohms or there-abouts), I placed the charging circuit across a pair of 6volt/7.7 AHr lead-acid batteries which I had on hand.
The ammeter started at just above 2amps charging, then tapered down to around 1.25 amps.Then I tried it across a 12v/7 AHr lead-acid battery with was already charged.The current started a just below an amp and within a minute, dropped to about 200milliampres or.2 amps. I say 'about' because the ammeter constantly wiggled theequivalence of.1 amp. I suspected that this might be caused by the noticeable ACripple in the DC line.
After all, there is no filtering on the rectified DC comingoff the full-wave rectifier.I located a 2 ohm, 50 watt resistor in my junk-box to replace the defective one whichhad originally caused my problem. Placing the charger wires across another charged12v/7 AHr battery it started the charge current at less than an amp. It also tapereddown, within a couple of minutes, to about.2.amps a shaky.2 amps. Theresistor did not even run warm but it had very little current through it.I finally found a.25 ohm/5 watt resistor and placed it in the place of the originaldefective white rectangular unit pop riveted to the back wall of the converter. Ifeared that the power rating on this resistor might be too low but I have used this onefor several months and it is holding up well.I reassembled my converter by going in reverse with the steps taken earlier todisassemble the unit. Everything went back together as easily as it had come apartand I was a happy camper (so to speak). I hope, if you are having problems as I was,that you can use some of this information and have as much success as I did.One additional piece of information the fan which you hear while the trailer isplugged into an external 117 v AC source, is actually running on 117 v AC rather than 12vDC and is thermostatically controlled.
A temperature sensor is attached to the aluminumheat sink which holds the power diodes. When they are doing their job and supplying12 volt power to your trailer (not particularly to the battery) those diodes will run hotand make the heat sink also quite hot. The sensor turns on the fan which blowsacross the heat sink as well as our now familiar power resistor. If you dont hearthe fan then the power converter is not having to do much work and the fan gets to rest.One other benefit on my converter is, I was able to clean up all the dust and'grunge' around the fan and it has become much quieter.
I still hear itbut nothing like it was previously.Just as a final encouragement for you to try to repair your own converter, when Ilooked up the replacement converter in a trailer accessories catalog, the replacement unitwas between $200 and $300. That was enough inducement for me to attempt my ownrepairs.Jim Pickett K5LADWritten June 29, 2002 - Updated 07/07/10Updated AdditionalInformationI received an email from Pete Sweeny with the following informationand I thought it was very worthwhile to add here:Good evening,I found your articlemost helpful.
I recognized the resistor as what is commonly called an ignition resistor orballast resistor. They were used in many Chrysler products before electronicignition systems came into use. I found that a Sorenson brand part number GCR7 will work,it is available at Advanced Auto parts for $3.88. It has no potting material around theresistance wire thus it will run cooler as well as a raised place where the unit fastensto the cabinet, this will also allow for better air flow.Thanks PeteI received another email from TomHolley in Canada.
He writes:After learning it was the same resistor as in the old Dodges, the same ones that weALWAYS had a spare of in the glove compartment, I checked that first. Ijumpered it with my ammeter when I had the battery out and all the lights in my camperwould work. They have not done that since I bought it used! No wonder mybattery would not charge while plugged in! I then removed it and ohmed it.open circuit. The new one cost me $8.99 at the Canadian Tire store part #18-4506 ( for us Canadians )I just wanted to thank you for saving me the cost of a converter!Thanks TomAlso I had foundsome other information which I've shared with several others who have have writtenme. I've copied this same part of a message to their answers several times, so itmight be best just to reproduce it here for anyone else.
The person had asked meabout replacing the fan and I sent him back the following information:Hi Dennis -I replaced my fan with a 117v AC muffin fan which was about 4'square, as I recall. These fans should be available in electronics supply stores,hamfests, or even computer stores. The one I used was from the surplus marketsomewhere and was one I had kicking around. If you go this route, be sure you get a117v AC unit as a lot of the fans you'll find surplus are 12 volt DC. The Magnatekfan only runs when you're plugged into city electrical mains.As far as other parts for the unit - 'official Magnatek parts'I once had a catalog I got from an RV store. I tried to find it today but, alas, noluck.
I dug back through some older messages and will copy what I sent to another RVerabout this book:Sounds like you found a pretty good deal and I think that might be wise.I might recommend that you find a book (actually a catalog) called '2004 RVParts & Accessories.' It's an 8 1/2 x 11 inch book that's just over3/4' thick. I got mine from one of the RV dealers in Tulsa and it was afreebie. I don't know if you've got some of those around you but it might beworth a call to a dealer or two. It's one of those books which is published for'the world' but has this dealer's name, logo, address, and phone numbers on thecover. They say that many of the items in the catalog are stocked but if you findsomething which they don't have, they can order it for you. Kinda like the oldSears and Roebuck catalogs.
In this catalog I found, not only brand new items(including power converters) but also some (note SOME) parts to repair existing equipment.For instance, on page 116 I'm seeing replacement parts for Magnetek Converters like: doorlatches, limit resistors, the PC board, fan motor, and relay. The prices aresurprisingly economical.Perhaps if you can locate a store with one of these books you could find adirect replacement for your fan. The truth is, the muffin fan I put into my unit isa LOT quieter than the old original fan.I received another emailfrom Mark Tabbert who wrote:I have a friend whoneeds help with his converter and I think I found the right place. He insists that it isthe fan or lack there of that is causing his converter to overheat. It does not trip thethermal breaker but the fan never comes on either he says. I was wondering if you could mewith the testing required to check the fan and the switch or heat sensor that controlswhen it is on and off?Thank you in advance,MarkMy answer to him might behelpful to others who have had the same problems and question:Hi Mark -I'm certainly no expert on Magnatekconverters.
I'm just someone who was desperate because mine was broken and Icouldn't find any information on the Internet about it. Necessity is the mother ofinvention, at least it was for me.If I were testing myconverter to see if the temperature switch was working, I'd set it up on the bench andblow a heat gun (or my wife's hair dryer) on it. If the converter was plugged in to110 volts AC and the fan didn't come on (with that heat on it), I'd know that either thefan was defective or the temperature sensor was bad. Actually when I store my trailer athome, I keep it hooked to the AC mains all the time. When I go inside on these really hotdays, my fan is usually running.
Not because the converter is generating lots of 12volt DC power, but because the excessive temperature closes the temperature sensor switchin my trailer. If the fan doesn't come on when you blow hot air on it, disconnect it from the AC mains and try the heat source again. Once it has beenheated up, measure across the temp sensor switch with a continuity meter - or a VOM (VoltOhm meter) set to low ohms. You should see either a short across the switch meaning thatit has closed or at least a low resistance (only a few ohms at most). If that testfails, the sensor is bad and must be replaced (try an automotive supply store). Ifthe switch closes with heat, then it's good and the problem is probably a fan which needsto be replaced.The fan is a 110v AC fan and not a12v DC fan like they sell at computer stores. Don't put a 12v DC fan in there - itwould run REALLY FAST but not for very long before you would let all the smoke out of it.Be sure anytesting you do with that meter and any replacement of any of the parts is done AFTERTURNING OFF THE POWER - the 110 v AC!!!!!!!BTW - If you must replace thetemperature sensor, they'll want to know what temperature it should close (be sure you getNO or normally open).
You might look on the switch itself and see if you can find astamped number for the temperature for it. If not, like I said, my switch is closingin a closed trailer on a hot day which is probably around 110-120 degrees so I'd startsomewhere around there.I hope this has been some help foryou and your friend. Good luck and 73, Jim - K5LADBTW - Yes, he needs that fan or itWILL overheat. Badly overheat. He will need to get this fixed.-Then I quickly added anothermessage:BTW Mark -I saw something just as I sent youthe previous answer.
If you must replace the thermal sensor switch, don't use theterm you used in your message here. The switch in the converter is NOT a 'thermalbreaker' but is a thermal sensor switch. The difference is, a thermal breaker is NCor normally closed and when it reaches a defined temperature, it OPENS and breaks thecircuit. The switch in the Magnetek converter is a NO or normally open switch and itcloses when the designed temperature is reached - when the converter is running and getsplenty hot and the fan is to start up to cool things back down.Again, I hope this helps.Jim - K5LADI received, yet another email from a reader who washaving a problem with his Magnetek converter. It didn't seem to be providing the 12volt DC power to the inside lights, motors, etc. When the battery was removed. Thisis the answer I sent him and, perhaps it might help someone else with the same or asimilar problem.
20, 2007)Hi Rodney -It's no bother and I'm glad to helpyou if I can but I'm no rocket scientist on these units. I just happened to have aneed to fix my own unit and couldn't find any info on the Internet so I had to do what Idid.If you're not real accustomed tolooking at schematics, you might sit down with a friend who is more up on that, but studythe ones showing the power supply parts and don't worry too much about the chargingsection. Maybe I should say study the bigger parts and don't worry about the smallerpieces in the unit.When the converter is plugged intothe AC from your home (or wherever) there's a relay which picks (pulls in) and suppliesthe 12 volts to rest of the trailer. If the battery is installed, that battery will beacross that 12 volt line in parallel.
If it's not there, the power goes from powercomponents (transformer, diodes, etc.) THROUGH the relay marked RY1 in the betterschematic prints, and on to the area with the battery, then on to the rest of the trailer.It will get to those connections up somewhere near where your big battery isstored. Again, even if the battery's not there, the voltage still goes on to theremainder of the trailer.If I understand your problemcorrectly, you're not seeing 12 volts DC to the internal things in the trailer which runon 12 volts (lights, heater motor, etc.) I'd check the relay first to make sure it'spulling in. You can do that without opening anything up just by standing by the converterinside the trailer and having someone plug your trailer into the AC. As soon as itsees the AC (there are no switches you need to throw) you should hear the relay snap in.It's not small and should be pretty noticeable. As I recall, it sounds likeit could crack pecan shells.If you're not hearing the relay,that's going to be your problem.If you're hearing the relay, thereare several places to look but it requires you to disconnect the converter from all thewiring and place it on the workbench for further checking.CAUTION: Be very sure you haveunplugged your trailer from the AC mains before you ever try to disconnect anything andremove the converter.You'll need to see if the powersupply is actually generating 12 volts. There a circuit breaker on the input(primary) side of the transformer but if your fan is running, that's not the problem.If you cannot measure 12 to 14 voltsat the input connection to the relay then the problem is either the transformer, a looseor broken wire, or one of the four diodes (marked D1-D4 in the schematic). An ACvoltmeter can verify that you are seeing 12-15 volts AC out of the transformer secondary.If all that checks out: relaypulling in, 12 volts DC to the input to the relay contact but no 12 volts DC out of therelay, the contacts are probably bad (dirty or burned up).
Parallax Power Supply - ADivision of Connecticut-Electric, Inc.It looks like the company is willing to sell a parts kit which includes several items.If that would fill the need for readers on this webpage, the order number is listedabove and the ParallaxPower link is listed above. Garret only needed and wanted theresistor to complete his repair so he continued to search available sources. The part number is MC14730 made by Multicomp.cost me$5.66 CDN.Thanks GarretI received another helpful piece of informationfrom another RVer, Karl Reichert. He wrote:Finally, after much searching, I have located a supplier of the fan temperature sensor(thermostat) for the model 6345 unit - I believe the company is inOregon, 1- 800-234-4328 part # 09526353 - unit set temp.
Cost less than$10.00. Company also carries many other RV parts, i.e. I alsopurchased parts for A & E awning. Regards KarlThanks Karl. That is a very valuable note.Thanks to Paul Burns, another RVer in Great Britain, he hascollected a lot of excellent information on the Magnetek Power Converters which includesmuch of the information we had placed on these web pages. Paul has offered toshare his information via these pages which should be a big help to anyone attempting torepair their unit.
You will find his collection on the next page here. Someof these items did not transfer to the webpages too well.
For instance, there is anice flowchart to help you, step by step, to find a solution to your problem. Thecomplete file, in.pdf format, is available for download. Thanks Paul.Here's another note from an RVer with someadditional information:Thanks a million for answering. Yes I do have a question. Icontacted Magnatek, (now Parallax).
All they would tell me is that my model (6300)is no longer in production and that I couldn't get parts. They wanted me to buyan upgrade kit for some $340.00. So I can't really affordthat. Here is what happened.
First my CO2 detector started going offafter Van sat not running for 24 hrs. I disconnected it, that silencedit. We then started driving, and smelled electrical burning.Then we heard this loudpop in the back of the van. Then I noticed my alternator gauge was discharging whilewe were still driving. I went directly home and disconnected my neg.Battery cable.
The engine abruptly stopped. My alternator. I put a new alternator.in at $185.00. There is aBatt. Isolator under the hood so I bypassed that in case it was bad too. Iwant to tell you before this all happened, there was no battery in the back. I hadremoved it about a year ago when it went bad.
Before my problem all the lights andappliances still worked in the rear with no battery back there, with the van running ornot, plugged in to a/c power or not. I was told that that should not be.
Thatis why I suspected the batt. IIsolator as being bad. I can buy a new isolatorfor $36.00. Any way, I removed the lower half of the Magnatek converter as peryour instructions. All I could find obviously wrong was the little ckt board wasblown. I found the schematic through your web site. C1 had exploded and R4 hadburned up. Also there is an SCR that I suspect is bad.
I know I can get thecap. And resistor but I cant find the SCR. The part # on the SCR is (T106A1) andthat is what I need help with. I'm sorry to be so long winded, but I thought youshould know everything about my experience.
I don't think anything else is bad inthe converter. I checked all the components. I have some knoweledge withelectronics but it's been a long time. I'm a retired computer Tech. From the 60'sand 70's. Was a radar tech in the Air Force.
Just to let you know I canunderstand most of what you saying to me about technical things.Can you help me with this? I'd really appreciate it.Sincerely, Jim EJim - All the information I have on the Magnatek converter has beenplaced on the website.
If a piece of information is missing, it's because I didn'thave it available to me. I hope you can find it through some other source.Good luck and 73,Jim - K5LADA ham operator from Texas is also an RVer and he'd done some really usefultroubleshooting the the Magnetek Converters. For a reader who also has someexperience with working with the electronics side of their RVs, this should beparticularly useful:Jim, here's my small contribution to Magnetek Converter lore:-Magnetek 6345 Power Converter - Charger, Simplified Theory of Operation.Pulsating DC Power is supplied to the dischargedbattery from T1, D1-D4, t hrough SCR1, R1 andCB1. SCR1 is conducting because its gate is held high by the 47 Ohm 2 Watt resistor anddiode D5. SCR2 is not conducting because its gate is held low by the 150 Ohmresistor. When the battery is fully charged, its Voltage rises to the13.8-14.2 Volt range as set by the 1 kOhm potentiometer.
A portion of this Voltage isapplied through the 1kOhm pot to diode D6, the 470 Ohm resistor and the 150 Ohm resistor.When the Voltage across the 150 Ohm resistor rises, the gate of SCR2 fires. This pullsdown the voltage on the two 47 Ohm resistors and on D5. This stops SCR1 from firing,thereby stopping battery charging. Battery charging will resume when battery Voltagedrops below the 13.8-14.2 threshold.-I'm in the throes of repairing my 6345, installed in a Winnebago Adventurer.
I burnt up(ran out of water) three or four WalMart FatMaxx 78 batteries in the last year.Overcharging. Voltage from the converter was 16.5-17 Volts at the battery.
I pulledthe converter according to your instructions. Thanks a bunch, they really helped.Only real difference I found was a cable restraining bracket screwed to the top of thebottom converter box. I had to un-screw the whole electrical box/panel and pull it out toremove the two screws holding the bracket. Then the converter box slid right out. Idid resistance checks and found nothing out of order. It appears that I was able to checkall of the components on the circuit board except SCR2 and the Zener diode D6, withoutremoving any leads nor un-mounting the board. Surprised me that there is little or nointeraction between the components.
I raise you to pay your precious attention here at what purpose, the program doesn’t have the power to form the 3D models themselves, and there’s conjointly no model information editor, however the developers counsel that we have a tendency to translate 3D models into 2nd formats, then you’ll print them out on the printer and so produce them from paper a true miracle. Link zum viiewer http www tamasoft co jp pepakura en download index html. If you are doing not believe American state, then attempt to check, I’m as naive as ever and that i believe the developers.Pepakura Designer Keycode will with quite completely different formats of 3D models, maybe, 3DS, DXF, MQO, LWO and lots of others, the list may be viewed on the official page of the program, i feel it’s straightforward.
The capacitor C1 check is not really sufficient.So I set up a car battery on the bench and powered up the converter. I found nineVolts at the D5-47 Ohm-47 Ohm junction, and 16.5 at the D5-SCR1 gate junction. Even thoughthe gate was back-biased 7.5 Volts, SCR1 was conducting.The bad component appears to be the pass SCR, SCR1. I really don't know what size SCRto get. I've got my eye on an NTE 5552. It is 25 Amps at 200 Volts. This seems to beenough, but with little current to spare.
I can get one at Frys in Arlington. I live about20 miles from Mouser electronics in Mansfield, but they no longer allow ordering at thestore.I can phone an order, then go pick it up (I think I still can). If you have heardwhat is the correct SCR, I'd like to know. I'll let you know how this one works out.All I know for now,73 TomTom - As noted in the previous note, the only information I have it what isshown here on the website. I hope you're able to find the inforormation you'relooking for. Good luck and 73, Jim - K5LADHere's another note from a ham in Californiawho provides some good information for others too. Thanks Bob-Hi Jim;Just thoughtId drop you a note to add to your info on the Magnatek converter.
Your site seems tobe a gathering point for miscellaneous and very helpful infoAbout a unit that a lot of people have but are notfurnished much information about for maintenance and repairs. I waspresented with a model 7455 the other day that was accused ofFRYING 2 large batteries in a fire department comm.
Trailer.I downloaded all of the Info that you had and then drilled out the poprivetsto open it up.I first looked for hot spots on thecircuit board ( there was only one board) found none only normal dust, then I went forthe large dodge power resistor, it wasnt there. I finally put all my infotogether and decided that this unit was over 25 years old. I checked thecooling fan, thank goodness I didnt plug it in to 110v.
The tag on the back ofthe fan said 12 vdc,plugged it in to a 12v battery and it worked like brand new. Bythis time I was beginning to wonder if this came from the same company. (it did).I put it back together ( except for the cover),I put a volfmeter across the DC output and a 0-10 amp ammeter in the + line and acar battery that I knew was about 95% charged on the output, plugged it in andstood back to see how much smoke would leak out, (none). The voltmeter read 13.9 voltsand the ammeter went up to 4 or 5 amps and then began to slowly slide down to about 400ma.