Fualty diode FR105? comments and available replacements please?

[AliTonto]

I have tested this diode out of circuit and although the voltage drop
is 0.47, I found that its forward resistance is 157,000 ohms and
reverse is 1.2 M
I believe these readings could cause it to not function properly
whilst in operation.
Can somebody please pass their thoughts on this and also tell me what
replacement for this diode FR105 is available?
Thanks.

 

[[email protected]]

I have tested this diode out of circuit and although the voltage drop
is 0.47, I found that its forward resistance is 157,000 ohms and
reverse is 1.2 M
I believe these readings could cause it to not function properly
whilst in operation.
Can somebody please pass their thoughts on this and also tell me what
replacement for this diode FR105 is available?
Thanks.

Does your meter have a switch for two different voltage levels when
using the ohmmeter? Sounds like it might be on the lower setting or you
are not using the correct setting on your ohmmeter to check diodes.

 

[Bill Jeffrey]

I have tested this diode out of circuit and although the voltage drop
is 0.47, I found that its forward resistance is 157,000 ohms and
reverse is 1.2 M
I believe these readings could cause it to not function properly
whilst in operation.
Can somebody please pass their thoughts on this and also tell me what
replacement for this diode FR105 is available?
Thanks.

It is a garden variety 1 amp 600 volt rectifier diode. It costs about
27 cents in single unit quantity. See, for example, mouser.com.

You can buy a replacement at Radio Shack for about a buck. They won't
recognize your part number, so just look for "1 amp 600 PIV". You might
also look for a 1N4005, 1N4006, or 1N4007.

By the way, your readings don't suggest to me that your diode is bad.
Most people seem not to realize that if you measure a diode with a VOM,
DVM, or VTVM, the actual ohms reading is meaningless. The only thing
that matters is that the two readings be very different. If both
readings are very low, then the diode is shorted. If both readings are
very high, then the diode is open. Other than short and open, there is
not much that can go wrong with a simple rectifier diode.

By the way, how did you measure the forward voltage? A forward voltage
of 0.47 indicates that it is conducting OK, but you put only a tiny
amount of current through it - much less than its design value.

Bill

 

[Phil Allison]

"Bill Jeffrey"

It is a garden variety 1 amp 600 volt rectifier diode. It costs about
27 cents in single unit quantity. See, for example, mouser.com.

** Every reference I can see on the net says the FR105 is a "fast
recovery" diode - that FR is a dead give away.

You can buy a replacement at Radio Shack for about a buck. They won't
recognize your part number, so just look for "1 amp 600 PIV". You might
also look for a 1N4005, 1N4006, or 1N4007.

** Not advisable replacements for a fast diode.

By the way, your readings don't suggest to me that your diode is bad.

** Yes they do.

Most people seem not to realize that if you measure a diode with a VOM,
DVM, or VTVM, the actual ohms reading is meaningless. The only thing
that matters is that the two readings be very different.

** It matters that the reverse reading is very high or open circuit.



If both

readings are very low, then the diode is shorted. If both readings are
very high, then the diode is open. Other than short and open, there is
not much that can go wrong with a simple rectifier diode.

** Ever heard of a leaky diode ?????

They play havoc in SMPS circuits.




.............. Phil

 

[AliTonto]

Just for anyone interested: from NTE site I found that a replacement
for this diode FR105 is RM1 (for any of you who sometimes rely on old
stock) .
AT

 

[AliTonto]

Just for anyone interested: from NTE site I found that a replacement
for this diode FR105 is RM1 (for any of you who sometimes rely on old
stock) .
AT

 

[Ol' Duffer]

It is a garden variety 1 amp 600 volt rectifier diode. It costs about
27 cents in single unit quantity. See, for example, mouser.com.

NO IT ISN'T. It is a fast recovery diode.

You can buy a replacement at Radio Shack for about a buck. They won't
recognize your part number, so just look for "1 amp 600 PIV". You might
also look for a 1N4005, 1N4006, or 1N4007.

Not unless it is a 60Hz rectifier. They usually have a good
reason for using fast recovery diodes, i.e. high frequency
switcher, scan-derived rectifier, etc. Trying to use a sloppy
low speed rectifier in any of these circuits will generate
lots of excess heat, probably burn up the diode, and maybe
damage other stuff in the process.

 

[AliTonto]

Hello all,
Thanks to those who clarified matters in my favour or shall I say in
favour of experience in electronics. (No offence is intended to
anyone.)
That is why the internet is such a great tool: we can share and learn
more together.
AT

 

[Bill Jeffrey]

** Every reference I can see on the net says the FR105 is a "fast
recovery" diode - that FR is a dead give away.

Phil -

You are right - I missed the Fast Recovery at the top of the page, since
the Mouser Search page listed it right along with the 1N4000 series.

Thanks for the oh-so-gentle correction.

It is still 27 cents. And I would still like to know how the forward
voltage was measured.

Bill

 

[AliTonto]

Hello Bill,
I used a DMM to measure the voltage drop on the diode out of circuit
as well as measuring the resistances.
Also, a common reason why one would be looking for a subtitute part is
that obtaining a newone can take too long.
A.T.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

I have tested this diode out of circuit and although the voltage drop
is 0.47, I found that its forward resistance is 157,000 ohms and
reverse is 1.2 M
I believe these readings could cause it to not function properly
whilst in operation.
Can somebody please pass their thoughts on this and also tell me what
replacement for this diode FR105 is available?
Thanks.

The FR105 is a common industry designation for a Fast Recovery 1A
rectifier. I think the 5 is the max voltage, but I can't remember what
that is. In any case, one of the 1N4937 series diodes should work. You
can also try www.nteinc.com for substitute parts.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

It is a garden variety 1 amp 600 volt rectifier diode. It costs about
27 cents in single unit quantity. See, for example, mouser.com.

You can buy a replacement at Radio Shack for about a buck. They won't
recognize your part number, so just look for "1 amp 600 PIV". You might
also look for a 1N4005, 1N4006, or 1N4007.

The 1N4006 series is *not* an adequate substitute! They are not fast
recovery and will probably overheat and fail.

BTW, regarding below, high conductance rectifiers may have less than a
half volt drop with currents much lower than their rated max. And he's
correct about the meter reading.