ARII-02 Insulation

monty_a900

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Hello Everyone

I'm getting 0V from the 10VDC unregulated output on a ARII-2 PCB. all other voltages are fine. No obvious burnt parts.

I did the Bob Roberts shotgun repair kit, but am confused as to what transistors need insulation. I've done as per Bob's instructions and still have issues;

http://www.therealbobroberts.net/aar2.html

However, if I use no insulators as suggested on Q5,Q7 & Q8, the metal screws will ensure Q3 (3055) case to short, won't it? I've seen other ARII boards have all insulated without issues?

Bob's instructions suggest;

Always finish up this job by checking to make sure there is no short between the case & the heat sink.

Surely this short will always happen unless Q5/Q7/Q8 are insulated?

Any help is appreciated.
 
The 10VDC comes off the transformer assembly. If you're missing that, you've got a blown fuse and/or a bad bridge rectifier.

Edward
 
AFAIK, the ARII-02 doesn't have any 10VDC output (AKA 10.3V or 10.6V, depending on which schematic you look at).

10VDC is an input to the board, and possibly a test point, but not an output.

Also, without 10VDC, there's no way I can see that you're getting any 5VDC output, unless some wires are crossed... the regulated 5V is derived from the 10.3V input.
 
Sorry, it's -5VDC and +12VDC I'm getting on the ARII-02. I've now noticed I'm blowing F2 & F3.

Any ideas?



AFAIK, the ARII-02 doesn't have any 10VDC output (AKA 10.3V or 10.6V, depending on which schematic you look at).

10VDC is an input to the board, and possibly a test point, but not an output.

Also, without 10VDC, there's no way I can see that you're getting any 5VDC output, unless some wires are crossed... the regulated 5V is derived from the 10.3V input.
 
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confused as to what transistors need insulation. I've done as per Bob's instructions and still have issues;

http://www.therealbobroberts.net/aar2.html

However, if I use no insulators as suggested on Q5,Q7 & Q8, the metal screws will ensure Q3 (3055) case to short, won't it? I've seen other ARII boards have all insulated without issues?

Bob's instructions suggest;

Always finish up this job by checking to make sure there is no short between the case & the heat sink.

Surely this short will always happen unless Q5/Q7/Q8 are insulated?

Any help is appreciated.

The metal heat sink is at ground potential. The tabs of Q5, Q7 & Q8 (two audio amps and a voltage regulator IC) are all connected to the ground legs, so it's OK to install them without any insulator (it's just another ground connection).

The case of Q3, however, is its collector; and it will be at 10VDC... and most certainly should NOT have ANY electrical contact with the (grounded) heat sink. This is why it must have an insulator. The screws should only connect the case of the xistor to the trace on the bottom of the PCB. You should not have any continunity between the collector (case) and the heat sink (i.e. they should not be shorted). If they are, it'll try to pull down the 10V (to 0V, ground), and a great deal of current will ensue, and fuses on the transformer assy will blow...
 
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