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Old 19th March 2008, 02:13 AM   #491
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Is this close to what you have? If so, changing the value of the resistors R13P or R12PA would change the regulated voltage. I'd try changing R12PA to ~2k.


http://www.bcae1.com/temp/HMR800-2Schematic.jpg
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Old 19th March 2008, 02:24 AM   #492
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It looks similar, but the problem is there isn't any regulation at all as it is right now. The circuit has no connections to the secondary voltage.
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Old 19th March 2008, 02:36 AM   #493
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What's different when looking at the connections to pins 1 and 2?

In your diagram, you showed an RC network between pins 2 and 3. That's generally only used when there is regulation. Is it possible that all that's lacking are the two 47k ohm resistors that go to the rails?

What's the voltage on pins 1 and 2 as of now?
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Old 19th March 2008, 03:03 AM   #494
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Pin 1 = 0.944v
Pin 2 = 4.991v

Pin1 and Pin2 look very similar to the sch other than the values of the resistors. There are also no 47k resistors to the rails.

I tried adding a 47k resistor from Pin2 to the positive rail and it didn't change anything. If I change the value of the 5.1k resistor the voltage changes though, even without the 47k resistor to the positive rail.
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Old 19th March 2008, 03:14 AM   #495
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Using both rails makes it a bit more complex but better also.

You will have to add both resistors. You want the rails to pull the voltages on pins 1 and 2 to ~2.5v.

For now, return the other values to what they were.
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Old 19th March 2008, 01:58 PM   #496
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If I add the resistors from Pin 1 to (-)rail and Pin 2 to (+)rail I get 3v on each rail. Voltage on Pin 1 is now -0.5v and Pin 2 is 5.6v. The voltages on those pins are also oscillating a bit.
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Old 19th March 2008, 04:12 PM   #497
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Pin 1 goes to the positive rail. Pin 2 goes to the negative rail.
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Old 19th March 2008, 04:33 PM   #498
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I swear it looks like Pin 1 is going to the negative rail in the schematic you posted.

OK, so I switched them and now I have 2.733 volts on both Pin 1 and Pin 2. There is no voltage on the rails now though.
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Old 19th March 2008, 04:51 PM   #499
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When you connected to rails to the wrong pins, it may have damaged the IC.

If the chip survived... It's strange that both pins have 2.7v and there is no output. If there's no rail voltage, what's pulling pin 1 up to 2.7v and what's pulling pin 2 down to 2.7v?
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Old 19th March 2008, 06:50 PM   #500
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The chip is OK, it still runs like normal if I remove the 47k resistors..

Tell me if this confuses you further..... with Pin 1 to (+)rail via the 47k and Pin 2 NOT connected to the (-)rail via 47k.....

Pin 1 = 4.993
Pin 2 = 4.996
(+)rail = 17.77
(-)rail = -17.87
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