Need help identifying surface mount components and finding a schematic

[Phil Strange]

For pictures and info please go to my website www.ocis.net/~ps


Thanks for any help you can offer

[Pooh Bear]

Post by Phil Strange
For pictures and info please go to my website www.ocis.net/~ps
Thanks for any help you can offer

A number of the components appear to be 'current shunts'. E.g. items 1 2
3 4.

Looks like 7 8 9 and 10 are simply links used to 'cross over' tracks
since this is a single sided board.

6 and 19 are puzzling. Conceivably a diode chip without encapsulation.

15 and 16 are standard leaded diodes of some kind.

12 and 13 are SMD transistors of some kind.

11 and 17 appear to be multi layer cermaic caps.

All the B s appear to be screened resistors ( this is typically done for
high quantity manufacture stuff )

Only able to reply to some newsgroups since not all are on my ISP's
server



Graham

[Phil Strange]

Thanks Pooh Bear
Will get back with other info.

Post by Pooh Bear

Post by Phil Strange
For pictures and info please go to my website www.ocis.net/~ps
Thanks for any help you can offer

A number of the components appear to be 'current shunts'. E.g. items 1 2
3 4.
Looks like 7 8 9 and 10 are simply links used to 'cross over' tracks
since this is a single sided board.
6 and 19 are puzzling. Conceivably a diode chip without encapsulation.
15 and 16 are standard leaded diodes of some kind.
12 and 13 are SMD transistors of some kind.
11 and 17 appear to be multi layer cermaic caps.
All the B s appear to be screened resistors ( this is typically done for
high quantity manufacture stuff )
Only able to reply to some newsgroups since not all are on my ISP's
server
Graham

[Fred Abse]

Post by Pooh Bear
A number of the components appear to be 'current shunts'. E.g. items 1 2
3 4.

Power diodes, I think.

Post by Pooh Bear
Looks like 7 8 9 and 10 are simply links used to 'cross over' tracks
since this is a single sided board.

Diodes, I think, look at the "oblique" views. Possibly aucxiliary supply
rectifier bridge.

Post by Pooh Bear
6 and 19 are puzzling. Conceivably a diode chip without encapsulation.

Thyristors. I think. 1K resistor gate - cathode.

Post by Pooh Bear
15 and 16 are standard leaded diodes of some kind.

No cathode marking. Possibly DIACs

Post by Pooh Bear
12 and 13 are SMD transistors of some kind.

Agreed, may be FETs

Post by Pooh Bear
11 and 17 appear to be multi layer cermaic caps.

Yes.

Post by Pooh Bear
All the B s appear to be screened resistors ( this is typically done for
high quantity manufacture stuff )

Yes.

Using the above identifications, the circuit appears to be a
half-controlled thyristor/diode bridge, which makes sense as a field
controller for an alternator.

Quite what the battery does, I'm not sure. Engine starting? Initial
excitation? If the diodes are all anode to lead, the latter is suggested,
but usually there's enough remanent magnetism to get things started, so it
may be a starting battery, and (1) is reverse polarity with respect to
(2), (3), and (4). (2) appears to be across the field output terminals,
and is possibly a back EMF suppressor of some kind.

It would be interesting to see the other side of the PCB.

[Robert Baer]

Post by Phil Strange
For pictures and info please go to my website www.ocis.net/~ps
Thanks for any help you can offer

I do not think you will get any more info this way.

If you know the unit in hand is good, or have two that failed
indifferent ways, you should be able to make measurements before
removing anything.
The film resistors, chip capacitors, and SOT-23 devices can be
measured by carefully cutting one or 2 traces for isolation.
What i previously indicated as 1A diodes could be un-soldered and
measured for breakdown voltage; current rating can only be approximated
via forward diode drop at known current (say 1mA to 100mA). Compare by
using same method with other diodes that have a known rating.
I then would remove the 1K shunt resistors and make similar
measurements on those "10A diodes" to verify their function, BV and
approximate current rating via the forward drop method. This way, they
have not been disturbed or ruined by "pilot error".
I also would not disturb any of the "jumpers", and make measurements
after isolating them via the cut trace methods.
The circuit is right on the board, so that part is simple; just a
matter of characterizing the parts.

[Phil Strange]

Thanks Bob

Apparently the center lead to part # 19 had broken loose. I reslodered this
an the board seems to function. When 120 vac is appliedto the AC pads, the
board supplies about 16 vdc to the DC pads. If AC drops, DC increases (and
vice versa) as it should.

Now, do I trust this board which seems to me to be poor choice of
construction in a vibrating, hot environment of a power generator ??

This particular repair was OK to do, but maybe fixing the next problem will
be impossible , so I would like to build a new board, more robust and easier
to fix.

Post by Robert Baer

Post by Phil Strange
For pictures and info please go to my website www.ocis.net/~ps
Thanks for any help you can offer

I do not think you will get any more info this way.
If you know the unit in hand is good, or have two that failed
indifferent ways, you should be able to make measurements before
removing anything.
The film resistors, chip capacitors, and SOT-23 devices can be
measured by carefully cutting one or 2 traces for isolation.
What i previously indicated as 1A diodes could be un-soldered and
measured for breakdown voltage; current rating can only be approximated
via forward diode drop at known current (say 1mA to 100mA). Compare by
using same method with other diodes that have a known rating.
I then would remove the 1K shunt resistors and make similar
measurements on those "10A diodes" to verify their function, BV and
approximate current rating via the forward drop method. This way, they
have not been disturbed or ruined by "pilot error".
I also would not disturb any of the "jumpers", and make measurements
after isolating them via the cut trace methods.
The circuit is right on the board, so that part is simple; just a
matter of characterizing the parts.

[Robert Baer]

Post by Phil Strange
Thanks Bob
Apparently the center lead to part # 19 had broken loose. I reslodered this
an the board seems to function. When 120 vac is appliedto the AC pads, the
board supplies about 16 vdc to the DC pads. If AC drops, DC increases (and
vice versa) as it should.
Now, do I trust this board which seems to me to be poor choice of
construction in a vibrating, hot environment of a power generator ??
This particular repair was OK to do, but maybe fixing the next problem will
be impossible , so I would like to build a new board, more robust and easier
to fix.

Post by Robert Baer

Post by Phil Strange
For pictures and info please go to my website www.ocis.net/~ps
Thanks for any help you can offer

I do not think you will get any more info this way.
If you know the unit in hand is good, or have two that failed
indifferent ways, you should be able to make measurements before
removing anything.
The film resistors, chip capacitors, and SOT-23 devices can be
measured by carefully cutting one or 2 traces for isolation.
What i previously indicated as 1A diodes could be un-soldered and
measured for breakdown voltage; current rating can only be approximated
via forward diode drop at known current (say 1mA to 100mA). Compare by
using same method with other diodes that have a known rating.
I then would remove the 1K shunt resistors and make similar
measurements on those "10A diodes" to verify their function, BV and
approximate current rating via the forward drop method. This way, they
have not been disturbed or ruined by "pilot error".
I also would not disturb any of the "jumpers", and make measurements
after isolating them via the cut trace methods.
The circuit is right on the board, so that part is simple; just a
matter of characterizing the parts.

The only thing "bad" is the use of ordinary solder in high temp
environments.
For reference, see http://oil4lessllc.com/Temps.pdf
I would measure everything possible, to get a good idea as to what to
use for making my own replacement - before putting that back into service.
It may fail in the same place and in the same way: electromigration
of the solder and resultant "cracking" (looks like cold solder joint).
Look for other places for cold solder joints.