• Husqvarna Motorcycles Made In Sweden - About 1988 and older

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electronics help. identify the triac in the sem cdi

T

ty w

Husqvarna
B Class
DSCN0317.JPGDSCN0319.JPGDSCN0324.JPGDSCN0325.JPG View attachment 22069 ive built the 4-stroke cdi as in the diagram and it works . ive takan apart the old cdi to find a bad diode. replaced it and it works again. but i noticed an extra cap and resistor, sort of buffering the charge voltage, and the trigger signal input resistors are different. unreadable triac so i removed it and compared it resistively to my new triac. interesting that resistance from trigger to cathode on new was like 70 ohm and the old one was about 25 ohm. thise differences leave me to think tthe triacs might have different trigger requirements.matched by different resistors. if so itll change the dwell time. si im hoping someone can help to figure out the triac chip. ive yet to find another 2 stroke cdi diagram on the net, its like the last piece of the puzzle. ill try to post a list of the available triacs too.....the easy thing to know is the voltage and the amperage is 400v 4A or higher, the turn on time seems almost a non issue because they are intended to operate at extremely high frequencies, but does the turn on time vary slightly with signal power. seems that within the 400v 4A variety, theres ones with different triger sensitivities- wattage and voltage as well as the reaction time(turn on time). so these differences i believe interact with how the trigger signal amplitude would increase with rpm to acheive an advance curve.im just a guessing that by the 2 stroke diagram showing the lower resistance for trigger signal to ground, draining more signal power, theres less power to trigger and so the 2 stroke must trigger at less voltage-power, thus the chip would internally have less resistance, so for less can still get through and activate. i should just put my old one back on and compare. but it would be nice to figure it out while im on the subject, id like to know for future if i ever need to change the chip. all this is inside the black sem cdi coil box. wine was marked sem amal x1 or 1x . i chipped at the plastic to find out the pc board was on the bottom on the flattest surface i gouged my way through just below the 2 bolt holes, right where the wires come out beside one bolt hole. about 1 cm below the bolt holes. so now the cdi and coil are separate joined by two wires. never did get to the big capacitor , its buried up along side the coil. the scr triac chips are only dollars each and so i might just get an assortment and measure each one to get one with similar resistances then try that one in the homemade to see if itll work as the 2 stroke schematic. it seems the triac series in the 4 stroke diagram works rather well but wont fire in the 2 stroke diagram i traced, leading me to question the triac internal resistance and trigger specs. if we could figure this out , we could build a cdi and affix it tothe old coilpack, after cutting the old one. make it rpairable DSCN0317.JPG
first pic is the two schematics, one is 4st from ktm 400 with sem, second is 2st off 84 husky wr 240, marked by X1 or 1X on bottom, now removed. you can see the numbers that got imprinted onto the potting glue, and cant read them nomore, also a dabble of solder to join the capacitor and coil leads, and that its now joined by two wires to cdi.
 
DSCN0327.JPGDSCN0328.JPG the first pic shows theback of the board with the soldered numbers that i suspect could be read with x ray or something, the second pic shows the diode that blew is top centre with silver stripe down, cheap part, i just want to know the part number for the 3 legged chip.
by the way the scr chip i used for the 4 stroke plans was the MAC210A8G 600v 10A and also a NTE5419 800v 12A. the nte one is apparently a trigger of 15mA and 1.5v max, whilst another NTE5629 is a 400v 4A and apparently trigger is <3mA and 2v max. thats if i even read the charts right and interpret info properly. i should have measured for any difference between nte5419 and the mac210a8g. its the mac210a8g that ive measured at 70 ish ohms trigger to cathode, and 25 ohms on the original 2 stroke sem cdi triac. both 4 stroke ones i built have run the engine but im driving on nte5419 i think.
 
and this sure looks about the same quality as whats in my old sem cdi, but the tracks are different. the original has a some sort serial number etched and tinned on the board as though to be able to read it with a scanner. this board doesnt have that feature. but if you look closely, the peices are labelled where they go... handy a bit, and im not sure if this and the previous post are the same circut? a second look and i see its the same triac # s6098
cdi_hq_wr250.jpg
 
and about the trigger sensitivity , the pic shows its Igt < 50mA max current. Igt means current through gate trigger, but i think it means the amount of current before gate fuses(shorts) . i think the gate will open before its max Igt, but im not sure . so in this conundrum i would like to figure out the triac from the bottom diagram in the first post
these last two pics were from places my google dont like to go either, and i couldnt read text but pictures and symbols work. and if anybody can help with the overseas internet it would probably help search better tham my own google
 
so i went to the electronics shop, explained the troblem and they were unable to suggest any triac to have less resistance across trigger. so i gambled and spent 3 shillings and a rupel to buy a more sensitive triac. brought home and measured and its like 150 ohms. this ones even higher resistance than the previous ones i bought. anywayse ill guess again and go back and buy one with less sensitivity this time and hope ill get one around 25 ohms . maybe less sensitive is more rugged, not so succeptable to blow if trigger spikes ?
the one i just bought was nte5629 and the resistance is wrong
 
when the input circut resistances are combined
4 stroke trigger circut resistance= 85 ohm, 100 ohm in reverse polarity
2 stroke trigger circutresistance=556 ohm, > 2000(diode test) may show open circut, thats ok

if one was to check resistances(green to black, then black to green) they should be as so. although if the chip is blown, this might not show, as its resistances only affect a portion of the circut.
on the red and/or orange the resistance only tests the first diode, resistance to black should be like open circut in forward and like 550 ohm in reverse polarity.

if this formula applies? power (watts)=voltage squared/ divided by resistance in ohms ... then

4 stroke: 5v x 5v / 85 ohm = 0.294 watts trigger, or .0588 amp, 58.8 miliamp
2 stroke: 5v x 5v / 556 ohm = 0.04496 watts trigger, or 0.00899 amps, 8.99 miliamp

but this is not power to the chip, rather its the amount of power the circut will draw, like comparing a 40 watt lightbulb with a 100 watt bulb. one has less resistance and uses more power, burning hotter. the triac chip does not heat up though, at least not in this application.

so im gonna look up more chips to see what i see
 
so i went back to the electronics store to get a less sensitive chip, and the sales/service personnel totally yanked my chain. they told me they dont know and the one i want isnt 3 bucks , its 10 bucks.. so i told them ill buy it if you can guarantee me the internal resistance value. they couldnt , nor would they open the pkg and measure it. i realize its only 10 dollar sale, with 90% mark-up, but its like they only want to sell by the number, without knowing what it does. or they at least wont share knowledge. if they have it.
on the computer the price is just under a dollar for a single , or down to 29 cents for 5000pcs. so theres no way it should be 10 dollars
 
as forthe one i built with 4 stroke? plans and NTE 5419 triac :
went through the carb... found the needle nozzle jet goes below level with carb throat when the main jet gets real tight.( as the main jet goes tight it can actually pull the air mixer part of needle jet depressed into where it fits . i thought it should be flush, so i pressed it out an then put it back in and only tightend until it sat flush with the carb throat. like a spacer washer or something is missing.
i then decided to look at timing as its retarded all the way to try to get other things to work. i discovered it was at a merely 0.4mm BTDC when it should be 2.55mm . so i advanced it as far as it would go without having to remove the flywheel, to access the stator screws. which was about 1.75mm BTDC. reassembled and went for a 30 km spin, and it was so much better. in fact i lost 4 whole knobs off the back trelleborg. ripped right off. so now im going to go and take off the flywhee, and advance the stator on the plate, eanough to be able to set the timing with the flywheel on, tightening by the stator mount screws thal are just barely accessible. so but the home built cdi works real good. three knobs in 4hours rating, without even trying.
 
i would like to identify the oridinal 2 stroke chip, but i will do a swap with the 4 stroke and my reconditioned 2 stroke and see if theres much difference. i cant identify the numbers on the 2stroke scr chip, they deteriorated whem i butchered the cdi, luckily without dammaging anything then being able to detect a bad diode , replaced and working butchered cdi.
 
as for the 4st schematic and cdi... ive yet to swap back to the 2st to see any difference of timing advance' but the factory spec of timed to 2.55mm BTDC isnt right for the 4st cdi. at this mark it has bad kickback and you can hear the preignition when running. ive now retarded the timing a couple of degrees , several times and its getting better. its probably around 12mm to 14mm on flywheel, when spec is like 20mm i think. its backed off the width of stator plate adjustment. so i want to retard it a bit more so i have to go under the flywheel to the stator screws to get more adjustment. all that said im quite positive that it offers less delay at idle, and so i suspect the actual advance curve be a bit different. might not advance as far at top RPM. when the timing was so far advanced it exhibited symptoms of over rich idle mixture, but with the timing adjustments, im finding the optimal spot, and the fuel mixture seems to be getting less rich. not sputtering and spitting oil, more steady rpm power at low throttle. regardless of getting it to the optimal timing spot, the home built CDI works good. and as im getting to the optimum timing spot, its burning less fuel with more power. i wonder if the timing dont advance so far at high RPM , might it be safer on the piston for over heating and melting? as thats how it blew originally, climbing a long road hill, heard the exhaust note change to a bit higher pitch , and when i eased off the gas it tried to stall, i gave a bit of fuel and like tings where tight inside it wouldnt rev up so i let it to stall. try kickstart and seized done. also plain 2st oil that day.
now that the timing is less over advanced, it sounds like the motor is rolling turning easyer, gettin more instantaneous explosion of power. not that it needs more, but i do want it to run perfectly spot on as possible. ive looked up the timing mark for this cdi model for 4st KTMbut they use the pinhole at tdc i think. whereas i need a measurement. my other bike has the pionts on a fixed stator plate. theres no timing adjustment, only the points gap, spec is 0.012 to 0.014 if i recall. when i was building 3 of them, i did the points different gap. first was 0.010 and it ran ok , no kick of powerband, just smooth and steady. the second was gapped at0.018 and there had kick back and quite a bit more power. the third bike was point gapped at the proper 0.014 and real nice, no kick back and ripped torque. they are all the same bike ,3 of them, so i then adjusted the second bike3 to the 0.014 from 0.018 and now it too ran so nice, no kick back and power on demand. thi first set to 0.010 i left there as the rider is not all there and frequently rides off through the ditch and forest until stopped by brambles and debris. and then responds that the bike has bad fn giro and just giro'd right off the road. i cannot go with that lunatic no more cause i dont want my ride interrupted with him getting speared by the forest. come to think of it i doubt that guy could balance on a fourwheeler.
 
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