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Old 13th June 2013, 05:54 PM   #121
nattawa is offline nattawa  Canada
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Quote:
Originally Posted by srinath View Post
I guess I need to round up a mouser order.
Cool.
Srinath.
Why do you think the transformer was shot? What did you do to it? Last time I came to this thread (moons ago) I thought you had the standby LED working and IC451 put out a 5.6V DC as supposed. Have you lost the LED and the 5.6V now?
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Old 13th June 2013, 06:06 PM   #122
srinath is offline srinath  United States
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It had 5.6 but not trip the relays.
Those relays are part of the soft start and got no voltage to them.
The trafo also tested continuity for an instant and then open.

Thought it was the trafo.

Cool.
Srinath.
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Old 13th June 2013, 06:19 PM   #123
nattawa is offline nattawa  Canada
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If you do have the 5.6V then the transformer is most likely good. What voltage do you have at R455 where it joins C466? You should have greater than 12V DC there. If you do have 12V or more there, do a quick test, pull fuse F452 (so that you don't power up the whole amp by doing the test), wire a 470 ohm or 1K ohm resistor from the 5.6V (at IC451 output) to the emmitor of Q456, you should engage all three relays (451, 452, and 453) by doing this. If the test turns out positive, measure the voltage at pin89 of IC701 (the Sony CXP micro) on the front board.

Last edited by nattawa; 13th June 2013 at 06:22 PM.
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Old 13th June 2013, 07:12 PM   #124
srinath is offline srinath  United States
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OK I will get this done, unless I did it earlier - your test seems awfully familiar to me - I will read through the old posts as well, I dont even remember some of it. I will read and try it - I have to replace the original transformer I guess.
Cool.
Srinath.
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Old 13th June 2013, 07:43 PM   #125
srinath is offline srinath  United States
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Default Not done

Quote:
Originally Posted by nattawa View Post
If you do have the 5.6V then the transformer is most likely good. What voltage do you have at R455 where it joins C466? You should have greater than 12V DC there. If you do have 12V or more there, do a quick test, pull fuse F452 (so that you don't power up the whole amp by doing the test), wire a 470 ohm or 1K ohm resistor from the 5.6V (at IC451 output) to the emmitor of Q456, you should engage all three relays (451, 452, and 453) by doing this. If the test turns out positive, measure the voltage at pin89 of IC701 (the Sony CXP micro) on the front board.
I have not done this test even though you ahve suggested it earlier.
I will get the board back to original and try it. I hope I didn't toss that old trafo.
Cool.
Srinath.
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Old 13th June 2013, 08:07 PM   #126
nattawa is offline nattawa  Canada
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I didn't realize you have taken the original transformer off the board....then with it off the board a simple resistance measurement to the windings should tell you it's likely good or bad, you can in turn decide to or not to put it back on the board for the test I proposed. The test was all about ruling out the failure of the standby power supply and failure of the relay drive circuit. You can do that test with your substitute transformer (from the tape deck), if its output voltage is within the ball park. It would not make any sense to put back a transformer that does not even pass a resistance test.

If you decide to get a new transformer, an alternative to mouser transformer would be to find a suitable voltage/capacity rating wall wart adapter in your parts bin and gut the transformer out.

Last edited by nattawa; 13th June 2013 at 08:09 PM.
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Old 13th June 2013, 08:17 PM   #127
srinath is offline srinath  United States
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I read through this whole thread -
This is what I observed in jan.

The transformer I pulled out made 13.4 volts ac. Its primary side tested like a capacitor. The one I put in made 10.4v ac. It tested like a resistor.

And the relays didn't click in either case.
If the original trafo is bad, I still ahve another issue ... maybe the one that killed that trafo - but its primary was bad - and the trafo I have in it, isn't enough voltage to do the trick.

Cool.
Srinath.
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Old 13th June 2013, 08:30 PM   #128
srinath is offline srinath  United States
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Default 18v dc

Quote:
Originally Posted by nattawa View Post
I didn't realize you have taken the original transformer off the board....then with it off the board a simple resistance measurement to the windings should tell you it's likely good or bad, you can in turn decide to or not to put it back on the board for the test I proposed. The test was all about ruling out the failure of the standby power supply and failure of the relay drive circuit. You can do that test with your substitute transformer (from the tape deck), if its output voltage is within the ball park. It would not make any sense to put back a transformer that does not even pass a resistance test.

If you decide to get a new transformer, an alternative to mouser transformer would be to find a suitable voltage/capacity rating wall wart adapter in your parts bin and gut the transformer out.
An 18 or so DC one would do the job right ?
OK let me look, I've been using those guys to power a slew of LED lights. Has to be an 18 v somewhere.
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Srinath.
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Old 13th June 2013, 09:33 PM   #129
nattawa is offline nattawa  Canada
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Quote:
Originally Posted by srinath View Post
I read through this whole thread -
This is what I observed in jan.

The transformer I pulled out made 13.4 volts ac. Its primary side tested like a capacitor. The one I put in made 10.4v ac. It tested like a resistor.

And the relays didn't click in either case.
If the original trafo is bad, I still ahve another issue ... maybe the one that killed that trafo - but its primary was bad - and the trafo I have in it, isn't enough voltage to do the trick.

Cool.
Srinath.
13.4VAC sounds a bit high.

I did a simulation with 11.3VAC and it puts out a DC voltage just above 13V at 135mA load current, which seems to be comfortable for the relays and their protection resistors. The red trace shows the DC voltage after the diode bridge, the green trace shows the wave form at the 5.1V zener D458. I'll post another simulation with a 18VDC and see how much difference there would be.
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Old 13th June 2013, 10:11 PM   #130
nattawa is offline nattawa  Canada
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With a transformer that puts out 18VDC @180mA load current, there isn't much change to the waveform at D458. But the relays may not be spec-ed to operate at such a voltage even with the 33-ohm protection resistors in place, and you may want to be careful. I'm not saying it will not work though.
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