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Zener Diode identification (color bands)

Discussion in 'Datasheets, Manuals or Parts' started by dalmation, Aug 15, 2008.

  1. dalmation

    dalmation Member

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    Hello,
    I am fixing a switch mode power supply and a shorted zener is giving me a headache.

    Can anyone help me identify the value, based on the coloured stripes?

    I'm lost? Thanks in advance.

    Zener.JPG
     
  2. Sceadwian

    Sceadwian Banned

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    I don't think those colour codes are standard like resistors, they're maker specific.
     
    • Disagree Disagree x 1
  3. dalmation

    dalmation Member

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    surely they can't be that cruel to me?

    Well, what would be the best guess?

    green, green, violet, 557...

    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).

    What a nightmare.

    -DAlmation.
     
  4. dave

    Dave New Member

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  5. Sceadwian

    Sceadwian Banned

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    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.
     
  6. dalmation

    dalmation Member

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    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.

    I'll see what they say?

    I'll report back how I get on.

    -DAl.
     
  7. dalmation

    dalmation Member

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    It turns out to be a 7.5V zener... still dont understand the colours, but I'm just happy to be able to fix it now!

    Thansk again for the help.

    -DAl.
     
  8. Sceadwian

    Sceadwian Banned

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    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.
     
  9. dalmation

    dalmation Member

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    Yeah, I agree.
    I went from 2A/700V to 3A/1000 volts.

    Had to widen the hole (0.8mm leads replaced with 1.2mm leads), but there was plenty of pad (only 1 layer pcb) so it wont cause any problems.

    Thanks again.

    -DAlmation

    PS: for the benefit of future searchers... it was a "Bauer XT32" television- incredibly common fault on this model in the UK.
     
  10. bombshadows

    bombshadows New Member

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    I think it depends on the supplier
     
  11. hishamuddinjohari

    hishamuddinjohari New Member

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    I also got problem with diode colour coding.

    i cannot sent the pictures, i don't know

    but the colour is Black (normal band), blue and yellow.

    Please help me
     
  12. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    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.
     
  13. bassbuddy

    bassbuddy New Member

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    Colour codes

    Hello there

    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.

    Bassbuddy
     

    Attached Files:

  14. andrew96

    andrew96 New Member

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    zd104 zener identification

    Hi

    Bauer XT32 psu, PSM210-417

    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!

    [​IMG]

    [​IMG]

    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!

    many thanks in advance
    Andrew
     
    Last edited: Mar 1, 2009
  15. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Last edited: Mar 6, 2015
  16. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    - active parts don't use color-number for alphanumeric codes , so no resistor color numbers.
    - 1st guess on mfg then look up color bands

    Davey it is often easier to reverse engineer the design and pick a better part going forward.

    If you can zone in on voltages or chips around parts with paper napkin schema, I can help.
     
  17. Davey1000

    Davey1000 New Member

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    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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