Help identifing resistor on roller door drive PCB. - Page 1
Forum section: electronics / repair

author: Sosh
author_rank: Newbie
timestamp: October 19, 2019, 03:13:38 am
content: Hi all,I'm hoping someone may be able to help me identify this blown resistor or hazard an educated guess at it's value,I have some theoretical training in electronics but noformal experience in repairs.It's from a BandD roller door drive,obviously some other damage on the board and a cracked BYW96E diode which I should be able to fix,no info or spares available from manufacturer.Thanks in advance

author: ozcar
author_rank: Frequent Contributor
timestamp: October 19, 2019, 04:39:12 am
content: You may get very lucky and somebody else has a similar one to look at, but beyond that I think you would need to trace out a bit of the circuit before anybody could take a guess.Edit with another thought:Something else that might work would be to find a picture of the board that is good enough to be able to read the resistor values. That also needs a lot of luck.I turned this one up. Obviously not the same, but some similarities. There is what justmightbe a 100 ohm resistor peeking out from behind the wire-wound resistor, but it is over near to the relay.https://www.aggdoors.com.au/online-shopping/bd/b-d-control-boards/

author: pbarton
author_rank: Frequent Contributor
timestamp: October 19, 2019, 08:55:46 pm
content: If you take the resistor out of the PCB, you may find the resistance, tolerance and wattage written on it. Its probably just hidden from view. ISO9000 requires everything to be marked!

author: Sosh
author_rank: Newbie
timestamp: October 23, 2019, 11:34:07 pm
content: Thanks mate,you got very close with that photo!I’ve tried the manufacturer and spares places but it’s probably 20 years old now...It’s a shame because it did the job just fine.Cheers

author: ozcar
author_rank: Frequent Contributor
timestamp: October 24, 2019, 12:58:47 am
content: We have a 20 year old B&D gate controller that is still going strong. Occasionally the limit switches play up, but no other problems so far.You probably would not need to trace out much of the circuit to get at least an idea of the resistance value - not much more than you would likely have to do in order to figure out why the resistor burned, and what else might need to be replaced.There are some places that specialise in repairing boards like that, eghttps://www.modulerepair.com.au/, but I guess at some point you cut your losses and move on.

author: mengfei
author_rank: Regular Contributor
timestamp: October 24, 2019, 01:49:27 am
content: you could do trial & error starting with a high value res, depending on the circuit.usually Low value resistors are the ones that get burned afaik

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: October 24, 2019, 01:04:00 pm
content: It looks as if the resistor is connected to the k end of the internal LED of the 4N25 opto-coupler. This is likely to be the current limiting resistor for the opto-coupler LED. This begs the question as to why it has burned. There is track connected to the k of the series diode too so maybe a fault elsewhereIf you power up the pcb and measure the voltage between pin 1 of the 4N25 and the far end of the busted resistor, then an estimate could be made of the value of the resistor as the max current of the LED is given as 60mA. Worth a try as the cost is near zero.BT

author: floobydust
author_rank: Super Contributor
timestamp: October 24, 2019, 10:24:30 pm
content: It looks like part of the motor overcurrent detect circuit. A jammed drive, or going past the limit switch might have happened, or the big shunt resistor went open circuit. The cut trace by D9 looks hokey.You could figure out the value if that portion is sketched out, but the opto is likely damaged too.

author: Syntax Error
author_rank: Frequent Contributor
timestamp: October 25, 2019, 02:48:08 pm
content: @floobydust : I was looking at the bare copper next to D9 too. Did the solder mask boil at this point or, is it just atest point? Zoomed in, there's sooty discoloring on the anode side of D9, with a soot trail reaching D10. So did R38 fail before or after D22 split? Is D22 still conducting?Incidentally, D9 is slightly out of line with the other diodes. So was someone on the production line not paying that much attention to bending wires correctly to avoid thermal cycling stresses when in use? Would it pay @Sosh to repace all of these diodes, either with direct equivalents or more robust devices?FYI BYW96 Datasheet:http://pdf.datasheetcatalog.com/datasheet/philips/BYW96_1.pdf

author: floobydust
author_rank: Super Contributor
timestamp: October 28, 2019, 06:21:52 am
content: I don't see a testpoint. D22 is cracked and the pcb trace by D9 was cut for some nonsense reason, D9's solder is cooked on one end. It might all (rectifiers) be for a brushed DC door motor? R38 might have arced to the trace under it.You'd have to sketch out the circuit with opto and R89 to see if it monitors motor current.I'd test/replace the diodes, fix the cut trace and the opto LED is likely dead. If it's for overcurrent detect, the opener should work without R38/opto.

author: Shock
author_rank: Super Contributor
timestamp: October 28, 2019, 11:48:17 am
content: Obviously be a bit safer than this guy but you get the idea.