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Old 24th December 2012, 01:35 PM   #11
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Quote:
Originally Posted by burbeck View Post
3V3A, is generally taken to mean 3.3 VA
In the same way:-
4V7 = 4.7 V
5K6 ohm = 5.6k ohm = 5600 ohm
4V7A. = 4.7 VA
4m7H = 4.7mH
This is Europe standard , where the decimal point is swapped for the units multiplier, I would guess this was introduced to reduce the number of markings on components as they get smaller, and to avoid using a "dot" which is difficult to see.For instance a zener diode 8.2 volts, 1.3W ,Would be marked as 8V2 1W3
This is correct for the decimal, 3V3 = 3.3V, but it's not VA. It means 3.3V DC supply for an analog part of a circuit, as opposed to supply for a digital part which could be 3V3D or 3.3V digital supply, as mentioned above.

jan
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Old 29th December 2012, 02:04 AM   #12
srinath is online now srinath  United States
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In the attached pic - I am not getting the relays to click. Both RLY 451 and 452.

What could be at fault. The transformer does seem to work fine, it gets warm as well as light up the LED for standby.
But the relays need to click on to get the big transformer to get into the circuit. What could be at work - or not at work here.

Thanks.
Srinath.
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Old 29th December 2012, 02:39 AM   #13
srh is offline srh  New Zealand
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Check that R452 isn't open.
Cheers,
Steve.
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Old 29th December 2012, 02:48 AM   #14
srinath is online now srinath  United States
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That is that massive resistor ? OK I will get to it tomorow and test it sir, thanks.
Cool.
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Old 29th December 2012, 04:21 AM   #15
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If resistor R452 check OKAY then check the voltage at the base of transistor Q456 should be positive to enable transistors Q451 thru Q55 and will enable both relay. Zero at the base will not enable the transistors Q451 thru Q455.
Also check the fuse for open.
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Old 29th December 2012, 07:31 AM   #16
sbrads is online now sbrads  United Kingdom
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Last year I fixed a newish Harman Kardon sub amp that only powered up into standby. It actually turned out to be a design fault IMHO. There was a mains ripple voltage detection circuit that turned the relays on; the cap in the relevant filter circuit was 1uF and my calculations showed if it was below 0.9uF the circuit couldn't work so I changed it for a 2.2uF and it's been fine since.
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Old 29th December 2012, 02:10 PM   #17
srinath is online now srinath  United States
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Thanks tauro0221.
Sbrads: I do believe that could be a possiblity in this amp too, but this one used to work in 2 channel. I find swollen caps on the dts board, and when I relaced it, the amp refused to power back up.
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Old 29th December 2012, 02:16 PM   #18
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Hi,
In that case recheck the solder to make sure you do not have a bridge solder.
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Old 29th December 2012, 02:57 PM   #19
srinath is online now srinath  United States
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The amp powered up without that DTS and video board in when I was working on that board.
Then after reassembly, it did not. Then I pulled the dts and video boards off and it still wont power up. I tried to power it on with every connection I disconnected, and still nothing. Up until now I had pulled everything apart and still not come out of standby.

The last step was to get the front board apart in case the tact switch wasn't working.

I have determined it is fine, so my choice now is to get the ideas you guys gave me, past that I guess I give up.

Cool.
Srinath.
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Old 29th December 2012, 03:57 PM   #20
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Hi,
I think you should get your voltmeter out and do some basic check. Make sure all the voltages are OKAY. If the relays are not closing check the voltage at the of base of Q456. Should be positive.
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