Identifying a zener diode

[tab a]

In attempting to repair a nice Sony boombox I found a bad resistor, zener and transistor. The zener is glass, and with the help of magnification, reads B56--I think! Googling leads me to believe that's a 56V zener, but how would I know it's not a 5.6?

This and the (bad) 2.2 ohm resistor are both connected to a D2058 (NTE377) transistor, if that's of any help.

Thanks.

 

[Andy1845c]

Is there anything more then B56 on it?
http://www.datasheetcatalog.com is a good source for component info, but "B56" brings up over 10 pages.

 

[RODALCO]

Have a look at the capacitor values on the power rails at the output of the zener .
If these are 16 Volts or 25 V , it's likely to be a 5V6.
If these are rated at 63 or 100 Volts it is a 56V zener.

 

[ljcox]

Why don't you measure it to see what its zener voltage is.

 

[Nigel Goodwin]

Why don't you measure it to see what its zener voltage is.

If it's faulty how could you measure it?.

On a more practical point, why not mention the model of the unit?, then people could try and check the circuit for you?.

You might also fill your location in, so people know what country to look in!.

 

[ljcox]

Good point. Perhaps I need reading lessons.

 

[Nigel Goodwin]

Good point. Perhaps I need reading lessons.

I'll send my wife round - she teaches 4 year old's top read!

 

[ljcox]

I'll send my wife round - she teaches 4 year old's top read!

Yes, send her immediately please.

 

[Gayan Soyza]

In attempting to repair a nice Sony boombox I found a bad resistor, zener and transistor. The zener is glass, and with the help of magnification, reads B56--I think! Googling leads me to believe that's a 56V zener, but how would I know it's not a 5.6?

This and the (bad) 2.2 ohm resistor are both connected to a D2058 (NTE377) transistor, if that's of any help.

Thanks.

This is what happens in most cases very hard to identify the real value.Replace the 56V zenner first & the damaged parts & check the circuit ,if no progress replace the zenner to 5.6V & check.If the circuit works on both cases a Problem comes.what is the correct value???.In this case any zenner value will accept current to flow.you need to consider about the other parts in the ciruit & check.needs a way of tricky.......

 

[Nigel Goodwin]

This is what happens in most cases very hard to identify the real value.Replace the 56V zenner first & the damaged parts & check the circuit ,if no progress replace the zenner to 5.6V & check.

Still waiting for the model number! - but assuming this runs on batteries?, like 6x1.5V or 8x1.5V - a 56V zener isn't really very likely?.

MUCH more likely to be a 5.6V zener, with the transistor an emitter follower forming a voltage regulator, and the 2.2 ohm a current limiting and safety resistor.

 

[tab a]

The Sony is a CFD-20. Yes it is AC or battery powered. Hadn't posted that as I'd hoped this might be obvious enough to those that are experienced that it wouldn't be needed, and I hadn't expected you to search out schematics for me. But--if someone has that schematic, it's D204 on the power supply board.

I don't know from power rails, but the two caps connected to the zener and the transistor are 10 and 16V, apparently lending credence to the 5.6V value?

Will put in some profile data.

Thanks for the help!

 

[tab a]

Hmmm...... Profile data already there. KS = Kansas.

 

[Nigel Goodwin]

Hmmm...... Profile data already there. KS = Kansas.

And the rest of the world are supposed to know that?.

Like I said, it's a 5.6V zener, here's the section of the circuit.

 

[tab a]

Thanks for the schematic Nigel. It's been educational--and a little perplexing.

Q212 and R275 are the other parts I've found to be bad. I'd not seen the symbol for R275 (or the triangle and exclamation point?) before but am going to guess it means a flameproof resistor--and that's why the resistor body is blue!? (Didn't know there were flameproof resistors until now.) Presumably the 4.7 is ohms? Mine is color coded a 2.2. Is the schematic perhaps an update? Can I get an idea of the power rating needed, by the size of this resistor?

From a theory standpoint, knowing the zener is shorted and the resistor is open, would it be likely that the zener shorted first, thereby destroying the transistor and resisitor, or have I got this backwards?

Thanks again.

 

[Nigel Goodwin]

Thanks for the schematic Nigel. It's been educational--and a little perplexing.

Q212 and R275 are the other parts I've found to be bad. I'd not seen the symbol for R275 (or the triangle and exclamation point?) before but am going to guess it means a flameproof resistor--and that's why the resistor body is blue!? (Didn't know there were flameproof resistors until now.) Presumably the 4.7 is ohms? Mine is color coded a 2.2. Is the schematic perhaps an update? Can I get an idea of the power rating needed, by the size of this resistor?

1/4W should be fine. The value might change by country?, either 2.2 or 4.7 should be fine - it's basically just a fuse.

From a theory standpoint, knowing the zener is shorted and the resistor is open, would it be likely that the zener shorted first, thereby destroying the transistor and resisitor, or have I got this backwards?

The zener going short wouldn't damage anything (except perhaps the 330 ohm feeding it?), what's happened is the transistor has gone S/C, resulting in the zener effectively being connected from input to chassis - this has overheated the zener, which has gone short. The zener going short has caused the resistor to go O/C, which is what it's there for.

It really depends if there was a short on the output of the regulator which killed the transistor?.

 

[tab a]

Thanks for the explanation, should help with my learning process--after I study it a bit.

How critical is the 1/4 watt rating? I found a place with really inexpensive shipping (for a $.40 part) but they only have 1/2 watt. If I need to stay with 1/4 I'll go elsewhere though.

Thanks.

 

[eng1]

How critical is the 1/4 watt rating? I found a place with really inexpensive shipping (for a $.40 part) but they only have 1/2 watt.

Since 1/2>1/4 they are even better!

 

[Nigel Goodwin]

Since 1/2>1/4 they are even better!

Except the sole reason for this resistor is to act as a fuse! - fitting a larger one wouldn't be an advantage in this case.

It should really be a specific fusible resistor, but this is only a small battery powered device - so a normal 1/4W or 1/2W resistor should be fine.

 

[eng1]

Except the sole reason for this resistor is to act as a fuse! - fitting a larger one wouldn't be an advantage in this case.

It should really be a specific fusible resistor, but this is only a small battery powered device - so a normal 1/4W or 1/2W resistor should be fine.

Actually I was thinking of the power rating of the zener diode! Sorry for that..
I undestarnd your point... with higher power rating the resistor wouldn't act like a fuse.

 

[tab a]

OK, I've spent some time pondering this power supply board, and the schematic you kindly supplied, Nigel, and have a couple more questions if I could:

Sony placed rows of white dots on some of the traces. They must have some purpose for them to go to the trouble?

From the schematic and looking at the board, it looks to me like the Q211 collector supplies 9v to the connector CN204. Q211 emitter is also at 9v. What's perplexing to me is that another end of the trace going to Q211 e is printed on the board as 12v, at connector CN204. I haven't been able to figure out a way for two ends of a trace to be at different potentials, unless they're being measured TO/across different points--common vs ground? Hope that makes sense.

Thanks.