*PHOTO* Need help- WHAT DIODE IS THIS?

studiot

Joined Nov 9, 2007
4,998
C'mon guys the object in the photo was point contact or germanium.

He should not substitute a silicon diode or the calibration would be wrong.
 

Thread Starter

bigcape

Joined Sep 18, 2009
158
This was a trouble shooting exercise for me.

I found a resistor that had one of the leads had been eaten also.

it was very fine line crack hard to tell.

This little 5.00 meter (as everyone is having such a hard time getting past) is what has started my electronics hobby.

There has been lots to learn from this $5.00 meter that is pricless and the education I have gotten will be with me for ever!

To master anything requires knowledge AND experience.

The person who knows enough to know what diode could replace this unmarked lowly 0.05 cent diode is truly a MASTER in his field.

I and anybody else will bennefit as well. That is what this site is all about right? "ALLaboutcircuits" ??
 

Thread Starter

bigcape

Joined Sep 18, 2009
158
I guess you have "reverse engineer" the PCB back to a schematic. Then we may be able to help.
THAT IS A GREAT learning idea!

There are not many components but the challenge will be the dial switch that has 24 I say TWENTYFOUR contacts.
 
Last edited:

studiot

Joined Nov 9, 2007
4,998
Judging from the age and pedigree of you meter I would go for a small signal germanium diode.

You need a fellow American to help you with a type number because UK numbering was substantially different in the days when ge diodes were popular - they started OA so I would use an OA 81 or OA 91.

Since you only have a single diode, I would check if it was actually in the signal path or strapped across the meter terminals (perhaps in reverse connection). This was very common in the days of analog meters. This was done to provide a measure of overload protection to the meter movement as the diode only conducted on overload. Most movements have an overall sensitivity of 0.1 to 0.2 volts, a germanium diode conducts at about 0.4 volts.
A silicon diode would not conduct until 0.6 volts, which may be enough to leave the movement damaged.
 

studiot

Joined Nov 9, 2007
4,998
Strangely enough I have just used an old Eagle analog multimeter I bought in 1969.

Daughter dear came home without her mobile phone charger so I had to lash up something on the bench.

Of course if I'm going for a 4 hour charge cycle and I want to monitor the current I can waste a heck of a lot of digital meter battery.
But an old analog one that happily monitors 50 - 150 milliamps at no cost - great.
 

Thread Starter

bigcape

Joined Sep 18, 2009
158
I guess you have "reverse engineer" the PCB back to a schematic. Then we may be able to help.

Here is the PCB. I have reversed the negative so you are seeing both sides the same for easier tracing.




By doing that then creating a schematic should be eaisier.

If you look at the bottom left you will see where I have removed a 1k15 Resistor and the DIODE of "MYSTERY"

I also did a trace repair with a silver pen. Thats why it looks different and squigly.

The far right are the outputs for the probes.

THIS MAY BE A FUN AND CHALLENGING EXERCISE FOR SOME!

EDUCATIONAL FOR THE ONE-TIME LOW PRICE OF $5.00 (while suplies last!)
 
Last edited:

Thread Starter

bigcape

Joined Sep 18, 2009
158
Strangely enough I have just used an old Eagle analog multimeter I bought in 1969.

Daughter dear came home without her mobile phone charger so I had to lash up something on the bench.

Of course if I'm going for a 4 hour charge cycle and I want to monitor the current I can waste a heck of a lot of digital meter battery.
But an old analog one that happily monitors 50 - 150 milliamps at no cost - great.
I see some of you guys are "slow statrers" takes a few wise cracks to get the experts to jump in.

One thing for sure you ALL are addicted to a challenge!
:)
 
Last edited:

beenthere

Joined Apr 20, 2004
15,819
Jameco may still have 1N34's.

bigcape - that resistor appears to be 1.15K (1,150 ohms), and not 1K5, or 1500 ohms. Old analog meters are typically full of non-standard resistance values.

Nope, 1.15K is in the 1% resistor values. 5 resistors (part #1.15KXBK) will set you back $.49 from Digi-Key.
 

Thread Starter

bigcape

Joined Sep 18, 2009
158
Even just seeing the board by side by side is hard to follow! I don't know how you guys do it flipping PCB's over one way then the otherside!!
 

Thread Starter

bigcape

Joined Sep 18, 2009
158
I know this isn't your meter, but attached is the schematic of a simpson 260.

It will give you a clue on how to lay out your schematic, if your so inclined.
I actually may be up for the challenge! Thank you.
 
Last edited:

Thread Starter

bigcape

Joined Sep 18, 2009
158
I know this isn't your meter, but attached is the schematic of a simpson 260.

It will give you a clue on how to lay out your schematic, if your so inclined.
JEEZE! There is no way I could build the METER from THAT!!!! GAME ON!!!!
 
Last edited:

studiot

Joined Nov 9, 2007
4,998
If you look carefully at Joe's circuit there are two sets of diodes.

Those labelled D1 & D2 form a half bridge in the signal path

Those labelled D3 form the protection diodes I mentioned earlier.

In you later picture there are a pair of what look like 1N4000 series silicon diodes.
I would guess these correspond to D1 & D2.

So that strengthens my contention that your mystery component is a germanium protection diode. Use the IN34.
 

Thread Starter

bigcape

Joined Sep 18, 2009
158
THE METER IS F.I.X.E.D!


So that strengthens my contention that your mystery component is a germanium protection diode. Use the IN34.
The advice was well taken. GO! GERMANIUMS!

She's ALIVE! She's ALIVE!

It's not worth repairing.
Get a new one and start over.
The process was expensive, no doubt.

The EDUCATION...........$$ priceless $$ (I got a bunch of cool S^!% though! A whole lab, eek! tweezers and all!)

As corny as it may:
Those that did not follow from the beginning, this was my first project that peeked my interest in electronics.

I didn't know what ANYTHING did except a Pot, though not it's name!

BOO-YAH!
 
Last edited:
Top