For good measure I am going to pull c463, 464, and c462 and see if the voltage improves @ pin 2.
Cool.
Srinath.
Cool.
Srinath.
There has to be a dead CD player round here somewhere ... Let me find it and see what it says.
Cool.
Srinath.
Cool.
Srinath.
Would this baby work ?
MR16 60Watt 60W Low Voltage Halogen Transformer 120V 12V MR16 | eBay
I think those leads give me the flexibility - LIke I can test it without having to remove the board and then get it off the board, etc etc.
Cool.
Srinath.
MR16 60Watt 60W Low Voltage Halogen Transformer 120V 12V MR16 | eBay
I think those leads give me the flexibility - LIke I can test it without having to remove the board and then get it off the board, etc etc.
Cool.
Srinath.
OK - liberated from a cassette deck, a 10.2 0 -10.2 v ac transformer. 50 watt capacity. And 2 x the size, but I think it should fit in the spot sideways. Or I can mount it outside of the board on top of the power transformer.
Anyway, I measured 13.4v to ground from the output leg of the original transformer.
Doesn't that mean its 13.4 - 0 -13.4 ?
Of course the original transformer doesn't have a center tap. Its center is the ground post of the diode bridge D454-D456 and c463 - c464.
The diode d453 in the 1 leg is used as a 1/2 wave rectifier, the resistor cuts down the amperage, then the cap, zener and resistor gets a proper 5v - can I get that 5v with a 10.2 - I think so - 10.2 with full wave will give ~15v dc, 1/2 wave should be ~7, I suspect the zener and cap should smooth it out ... it may lack the amperage, maybe I can take that 4700 ohm guy r453 down to say 3500. Anyway I think the first try I should leave it as is.
Then the 7806 circuit - I think it should work just fine running 10.2 0 -10.2 to 6v. Just the same as it did with 13.4.
That leaves the third leg - the ones feeding the relays 12v - 10.2 0 -10.2 should work fine there too, unless there is something is going to cut it down more.
Cool.
Srinath.
Anyway, I measured 13.4v to ground from the output leg of the original transformer.
Doesn't that mean its 13.4 - 0 -13.4 ?
Of course the original transformer doesn't have a center tap. Its center is the ground post of the diode bridge D454-D456 and c463 - c464.
The diode d453 in the 1 leg is used as a 1/2 wave rectifier, the resistor cuts down the amperage, then the cap, zener and resistor gets a proper 5v - can I get that 5v with a 10.2 - I think so - 10.2 with full wave will give ~15v dc, 1/2 wave should be ~7, I suspect the zener and cap should smooth it out ... it may lack the amperage, maybe I can take that 4700 ohm guy r453 down to say 3500. Anyway I think the first try I should leave it as is.
Then the 7806 circuit - I think it should work just fine running 10.2 0 -10.2 to 6v. Just the same as it did with 13.4.
That leaves the third leg - the ones feeding the relays 12v - 10.2 0 -10.2 should work fine there too, unless there is something is going to cut it down more.
Cool.
Srinath.
Hi,
If the original transformer read 13 volts it will give you 13 x1.4 = to 18 volt DC. If the CD transformer read 10 volts then it will give you 10 * 1.4 =14 volt DC. I will not worry about the voltage going to PIN 2 connector since it goes thru the 4700 ohm resistor. Did you check Mouser to see if they have a transformer close to the one use in your amplifier? They may have one. No exactly but one that you can install inside of the cabinet.
If the original transformer read 13 volts it will give you 13 x1.4 = to 18 volt DC. If the CD transformer read 10 volts then it will give you 10 * 1.4 =14 volt DC. I will not worry about the voltage going to PIN 2 connector since it goes thru the 4700 ohm resistor. Did you check Mouser to see if they have a transformer close to the one use in your amplifier? They may have one. No exactly but one that you can install inside of the cabinet.
Before you replace the transformer make sure you do a good visual check to the PS board for crack tracers or bad solder joints. If it is possible use a magnifier glass to check for trace cracks etc etc.
I will inspect it for sure, but I have looked at it like crazy, I think the short I had - R456 to C478, I dont have that any more, it may have happened a long time ago, or when I pulled it apart one of these many times when working on it before it went DOA - anyway that may have been what killed the trafo.
Now there is no 18v anywhere in this board, 5v, 6v, and 30v. The 30v may have the main power transformer powering it.
Cool.
Srinath.
Now there is no 18v anywhere in this board, 5v, 6v, and 30v. The 30v may have the main power transformer powering it.
Cool.
Srinath.
I swapped out transformers ... and still no relay click.
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.
I think something else is blown up on it.
I will be poking around on it tomorow.
And follow the other points in this thread.
Cool.
Srinath.
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.
I think something else is blown up on it.
I will be poking around on it tomorow.
And follow the other points in this thread.
Cool.
Srinath.
Hi,
If it read as a capacitor the primary it is open. Now What it is the DC voltage with the new transformer ? Do you still have 2 volt at the connector CP458 pin 2? To be able to close the relays you need a positive signal at the CP458 connector pin 1. Also what it is the voltage at the CP458 connector 4? Do you have 6 volts?
If it read as a capacitor the primary it is open. Now What it is the DC voltage with the new transformer ? Do you still have 2 volt at the connector CP458 pin 2? To be able to close the relays you need a positive signal at the CP458 connector pin 1. Also what it is the voltage at the CP458 connector 4? Do you have 6 volts?
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.
Tomorow I'll get back at it.
Cool.
Srinath.
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.
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.
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.
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.
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.
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.
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.
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.
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.
It could be one of those transistors getting the voltage to the relays. I'll start pulling them and checking.
Cool.
Srinath.
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.
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.
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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.
Thanks.
Srinath.
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.
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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