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Old 13th January 2013, 12:58 AM   #91
srinath is offline srinath  United States
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I didn't have time today to check - I pretty much put the trafo in and that was it.
Tomorow I'll get back at it.
Cool.
Srinath.
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Old 13th January 2013, 10:09 PM   #92
srinath is offline srinath  United States
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Pin 4 6.32 v dc, pin 2 2.72 vdc.
I cant imagine what could be wrong, I guess the 5v zener, or the resistors, or the cap or the diode.
I will buy and swap those ...

Now is 6.32 under no load acceptable on 4 ? Or is my 7806 dead.

Cool.
Srinath.
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Old 13th January 2013, 10:40 PM   #93
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Hi,
Pin 4 it is OKAY should be 6 volts. Now pin 2 should be 5 volts. Check the voltage between D453 and the resistor R453.
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Old 13th January 2013, 10:57 PM   #94
srinath is offline srinath  United States
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OK I can check that in a few days.
I was thinking I'll put in a new trafo and ding ding ding was gonna be a bright and shiny new amp.
OK I guess I am learning more and more.
Cool.
Srinath.
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Old 13th January 2013, 11:34 PM   #95
nattawa is online now nattawa  Canada
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I did not follow the entire process, but I wonder why you people are seeking 5V at the zener D458. I think 2.7-2.8VDC across D458 on a multi meter is about right.

The RC time constant that C465 gets discharged at is only 2.6mS, and the C465 has a discharge time of at lease 8.3mS between charge cycles. That means you should never get a 5V DC reading across D458. If you use an oscilloscope to probe D458 you'll see a waveform that looks like a saw blade with all the teeth being chopped off half way so that they have a flat top at 5V level.

The problem seems to lie somewhere else.
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Old 13th January 2013, 11:43 PM   #96
srinath is offline srinath  United States
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OK, if 2.7v dc is fine @ pin 2 cos its the bottom of the saw tooth - with a 5v peak, OK I can see that - then the problem is my relays are not clicking - they dont have voltage across the magnet coil.
It could be one of those transistors getting the voltage to the relays. I'll start pulling them and checking.

Cool.
Srinath.
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Old 13th January 2013, 11:56 PM   #97
nattawa is online now nattawa  Canada
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2.7-2.8VDC is the average. The bottom of the saw tooth is well below that. I'm not sure replacing the 13.4VAC transfo with a 10.4VAC one will cause you trouble, as the level at the bottom of the saw tooth has changed by that. Increase the value of C465 can raise the saw tooth bottom level, if in doubt.

It's easy to test the relays and their driving transistors. Just pull the fuse F452 (13A/125V), so that you don't power up the amp by doing the test, then wire the IC451 output to the base of Q456 through a 1K resistor. If that does not activate the relays, check the transistors and solder joints and such. If that does make the relays work, look elsewhere.

Last edited by nattawa; 14th January 2013 at 12:09 AM.
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Old 15th January 2013, 12:57 PM   #98
srinath is offline srinath  United States
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I will try that in a bit. I am not plugging in the main transformer at all, so the amp will not come up, its only the relays I am looking at. I am not even connecting the display.
Thanks.
Srinath.
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Old 15th January 2013, 01:45 PM   #99
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Hi,
The problem we were looking for 5 volts at pin 2 it is that for the micro to see a logical one the voltage should be 3 volts or higher. Below 3 it can be a zero. The micro it is the one that enable the relays by sending a signal to enable the relays. I am not sure if for the micro to enable the relay it need pin 2 high. That is why we are looking a 5 at pin.
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Old 15th January 2013, 02:13 PM   #100
srinath is offline srinath  United States
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I thought the relays are clicked on by the other branch - the 3rd one, the 5v zener is 1, the 6v 7806 is another and that transistor set is fed by the other part which would be double wave rectifed DC ...
Thanks.
Srinath.
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