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5.57V zener sounds a bit exact, what about 5.5v zener and violet just some suffix?
Sound plausible?
There is only one other zener in the circuit (different colours, though). I suppose if I measure the voltage on that, then scan a few dozen datasheets, I might find a match for that one (then work out the mysterious diode).
Trace it back to what power rail it comes from that will give you a clue, if this is a discrete power supply take a look around the rest of the circuit, the zener was likley run by an opamp for gain and drive and then buffered, (the opamps should probably be replaced as well) The resistor network on the opamp will tell you what voltage the reference was adjusted to so you can determine the actual zener voltage.
its connected to a FSD210D IC. It is connected in series with a 38K resistor and the phototransistor of an optocoupler (which have both blown too)
I dont think I can work it out to be honest.
I found a shop that sells a repair kit for this exact fault. I have already replaced the FSD210D IC (exploded part), a shorted diode (which caused the problem) and some burnt out pcb tracks. I have emailed them and (cheekily) asked if I can just buy the optocoupler, Zener and resistor.
If it's a common enough failure to warrant a special kit you may want to think about replacing the diode that did it with a slightly over rated version.
The overrated diode idea sounds great. I've done that with a TV power
supply before and it worked for a long time after that. Sometimes the
turn on surge gets it, but an overrated part (actually the RIGHT rating as
the original wasnt spec'd high enough) handles it much better.
I've seen these colour codes before. Could it be a 1N755 from the (often used) series in attached data sheet? That happens to be a 7,5 volts zener. I don't know if they are produced as SMD, but I suspect they will be.
Does anyone know what voltage the zener is for ZD104? I know its is a BZV55 but no idea on the voltage, I think it has a red, red, blue bands reading from the cathode. The second picture shows the zener removed but the colour bands look alot clearer stuck in the glue!
**broken link removed**
**broken link removed**
It is conected between the base and earth so presuming it is limiting the base voltage from going to high and saturating the transistor (BC858 Q307) which was open circuit (so not switching the next switch mode powers supplies on to supply the 12V and 24V rails) I believe the BC858 has 12V on the collector which is used as a switch to pass it on the the Emitter, the base gets its turn on/off voltage via 2x 4.7k resistors and a optocoupler from 12V also, the zener is from base to earth, what is likely to be the voltage of this zener.
Chas Hyde list Kit15 and Q307 is listed as a BC858 a PNP, but i have my doubts on this as the circuit sugests it is a BC850 or BC848 NPN, can anyone confirm what transistor Q307 is?
I know DZ301 connected to the FSD210 is 7.5v and has violet green green bands (shown in the first post on this page reading from the cathode) and is also a BZV55 but this one survived! it is the ZD104 thats short, can anyone help please?
this has happened due to the usual 5V standby circuit blowing up which is now fixed and supplying 5v as it should
I just need to replace this zener and transistor to see if psu works, if not its going to be IC101 and i will get the kit, dont want to spend out £40 on the kit if i dont need the IC's!
I'm trying to repair an Electric Shepherd ESB 250 electric fence energizer (12 volt battery driven) Its problem is the use of non-Milspec components which have steel leadout wires. As it is a battery fencer it will have been used outside in all weathers and the damp atmosphere has corroded away the leads on several resistors and diodes (join steel and copper then get them damp = a corrosion cell) There is one glass diode with bands White Black White Black but the black bands are very thin. I thought that it might be a 1N9090 but this number does not compute. Probing up the hole where the lead used to be shows that it is a diode (the lead at its other end is still OK) It looks like I will have to reverse-bias what is left of it to try to discover its Zener voltage. Curiously the PCB had been varnished by the makers but it looks as if the varnish was also not Milspec. IMHO car body cavity wax protects better than varnish but of course nothing lasts forever. If anyone can ID that weird diode I'd be very interested to know what it is.
Update I have just discovered that there is a 1N99 but whether this is it I don't know. The 1N99 is Germanium which is rather surprising but of course the unit is very old. Unfortunately the circuit diagrams for these things seem to be Trade Secrets as the makers would really like their customers to buy new products.
The overrated diode idea sounds great. I've done that with a TV power
supply before and it worked for a long time after that. Sometimes the
turn on surge gets it, but an overrated part (actually the RIGHT rating as
the original wasnt spec'd high enough) handles it much better.
Another way is to use an inrush current limiter (NTC Thermistor) which is high resistance when cold but low resistance when it warms up. Of course these thermistors do run hot so often they are wrapped in heat resistant sleeving. They are sometimes fitted to the larger size angle grinders to try to reduce the starting kick. Such thermistors also prolong switch life.
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