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PostPosted: 04 Feb 2012, 05:55 
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Joined: 08 May 2009, 08:20
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Location: Duesseldorf, Germany
Hey,

a 10A slow blow fuse surely is the right one.
The manual shows a power consumption of 1200Watts (both channels active) which does fit the current rating of the fuse. 10A x 115VAC = 1150VA (transformer primary).
Please measure the rectifier bridge again. Set the DMM to the rectifier mode (continuity mode) and connect the positive probe to the "+" (positive) pin of the rectifier.
Both AC pins should read about 0.5 to 0.7 and the negative pin +0.2 (0.7 to 0.9). It is right that the caps will slightly charge up during the measurement.
We can assume that the bridge is OK when the readings start at 0.5 / 0.7 and then rises to 1.4 and more. In each case, both AC pins should give equal readings, the "-" a bit more
and you must(!) get a positive signed value at each AC pin.

I think you can fire up the power supply board for testing later. But - please unplug the wires going from the power board to the amp circuit board (remember the wire positions).
I don't see any reason why it shouldn't work for testing when the rectifier is OK. If the power board has an issue it doesn't work properly anyways.
Test the voltages with the DMM (especially the blue wires and the black one - blue to blue; and both blue to black).
The probe tips should easily slide along the clear plastic isolators to reach the faston plugs.. It is Interesting to know the output voltage of the transformer. We will know if the transformer is OK so.
Measure the voltages at the molex plug (the white plug next to the L7812 / L7912 and R03 / R04). Check the regulators for temperature. The PCB is tinned, so the tracks are able
to handle high currents. It is very (!) unusual that the PSU PCB became hot (blackened surface).

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 04 Feb 2012, 14:28 
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Joined: 25 Jan 2012, 15:39
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Hi Tom. I remeasured again, and if I'm reading things correctly, I'm pretty sure I'm doing it right. I'm including some photos of what I'm actually measuring. Is this right?
Image
Image
Image
Image
Image


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PostPosted: 06 Feb 2012, 17:52 
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Location: Duesseldorf, Germany
Hi,

after reading the DMM manual, we can assume that the rectifier bridge is OK. Both AC are OL and "-" is about double the forward voltage. Good!
Besides the fuse and the (unchecked) transformer i don't see any reason why the PSU shouldn't work for testing.

Time to fire up the board with the right fuse and let's take a look what happens then - whether the fuse will blow again or you'll be able to get some reasonable voltage readings from the PSU.
myself wrote:
Test the voltages with the DMM (especially the blue wires and the black one - blue to blue; and both blue to black).
The probe tips should easily slide along the clear plastic isolators to reach the faston plugs.. It is Interesting to know the output voltage of the transformer. We will know if the transformer is OK so.
Measure the voltages at the molex plug (the white plug next to the L7812 / L7912 and R03 / R04). Check the regulators for temperature. The PCB is tinned, so the tracks are able
to handle high currents. It is very (!) unusual that the PSU PCB became hot (blackened surface).
Be sure the PSU board output is unplugged from the amplifier board.
BTW - i have the bad feeling that the regulators and the resistors are totally undersized. This might be the reason for the discoloration / heat spot on the power supply board.

When you have some more time, check all resistors and all Transistors / FETs of the amp board for discoloration (black or brown spots, broken or cracked transistor packages)

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 10 Feb 2012, 11:22 
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Joined: 25 Jan 2012, 15:39
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Hey guys. Sorry I've been MIA. It's been a very busy couple of weeks straight but I am still eager to get this guy going. I will do as you recommend and attempt to power up the board with the amplifier section disconnected. I'll report back on the outcome.

Thanks.


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PostPosted: 21 Feb 2012, 15:32 
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Joined: 25 Jan 2012, 15:39
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OK, so, with the Inlaws visiting and a busy work schedule, I've had minimal time for the fun stuff. I did finally manage to put the power supply board back in and attempted to power up the amp. I hooked up the wires coming from the transformer, but left the amplifier section disconnected. It did not blow the 6.3 amp fuse, but I am unsure as to what to check for before proceeding. There was no delay relay click or power light on the front panel, but I think that is because the amp section is still disconnected. I did find that the surge suppressor capacitor was bad, I haven't been able to find a suitable replacement locally so I will have to order one. Would that capacitor cause it to not power up? Can I continue with this while I wait for it to arrive? With the amp section disconnected, what should I check/measure/verify before connecting the amp section?


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PostPosted: 27 Feb 2012, 19:02 
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Location: Duesseldorf, Germany
Hey again,

sorry for the late one.
Quote:
I hooked up the wires coming from the transformer, but left the amplifier section disconnected. It did not blow the 6.3 amp fuse, but I am unsure as to what to check for before proceeding.
OK, i have a better overview now. The fuse can't blow when you switch on the PSU. The transistor on the PSU board switches the relais on or off. I think you guessed right.
When the amp section is disconnected, the transistor doesn't switch the relais and the transformer's AC outputs are cut off from the rectifier bridge.
Quote:
Would that capacitor cause it to not power up?
Actually not. The cap is mounted to eliminate the switching noise or switch arcing.
Are you talking about the blue disk shaped cap mounted under the power switch? Is it not a simple ceramic disk cap (22nF or somewhat)??
Quote:
With the amp section disconnected, what should I check/measure/verify before connecting the amp section?
Good point. Actually nothing now.
The only thing you can do now is connect the PSU board molex (24, pwr, 12+, 12-) to the amp board and see what happens. My guess is that the relais should switch on and
the fuse (6.3A) could blow short after. The power caps should charge up fast and they behave like a short circuit in the first moment. 6.3A is little weak then.
The amp doesn't have a "soft start", but the "low power" section (24V and 12V) is seperated from the power section. The fuse might survive...
Don't you have some 10A fuses?? This would really help a lot.

Now - when you can get the PSU up and running with the low voltage molex connected, it is sure that the transformer doesn't have a short on the primary winding...
BTW - I don't believe that the amp section is gone bad... I have the bad feeling that the only problem is the fuse or the transformer...

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 28 Feb 2012, 00:12 
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Joined: 25 Jan 2012, 15:39
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Hey Tom, good to hear from ya. The cap I am referring to is a rectangular, 275V .19uF item and it is soldered to the power leads where they enter the back of the amplifier...on the back side of the IEC connector. I don't think it should effect functionality, but I ordered some anyway and will put it in when it arrives.

I will hook everything back up tomorrow and try to fire it up, fingers crossed. I don't have any 10a fuses. I can't find any around here. The 6.3's are the closest I can find.


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PostPosted: 28 Feb 2012, 14:40 
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Joined: 15 Jan 2011, 10:53
Posts: 41
Location: Darmstadt, Germany
Hi,

as the cap is mounted across the power lines only a type X capacitor should be used. The cap you described is part of the line input filter and should therefore be treated with special care.
You probably won't get far with a 6.3 A fuse. Your multimeter seems to be of the clamp type, so you can safely check the power consumption of the amplifier while it's turned on. That will give you an idea if there are problems with the amplifier PCB.


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PostPosted: 28 Feb 2012, 14:59 
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Joined: 25 Jan 2012, 15:39
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ferdinandkeil wrote:
as the cap is mounted across the power lines only a type X capacitor should be used. The cap you described is part of the line input filter and should therefore be treated with special care.

Yes, you are correct. It is an X2 type of capacitor. 0.15uFK 275V X2 to be exact. The closest I could find was a 0.22uFK 275V X2 model. I assume the small difference in capacitance will not negatively effect it?
ferdinandkeil wrote:
You probably won't get far with a 6.3 A fuse. Your multimeter seems to be of the clamp type, so you can safely check the power consumption of the amplifier while it's turned on. That will give you an idea if there are problems with the amplifier PCB.

Well, I'll give it a shot with the 6.3 and see what happens. If it blows, I'll order some 10A's. I will give this a try when I get home in a bit.


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PostPosted: 30 Oct 2016, 16:18 
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Joined: 30 Oct 2016, 16:16
Posts: 1
Did you ever get it working? I stumbled across this searching part #'s for my Amp300 that I have been troubleshooting. Perhaps your expertise with this power board can help me. There is already a lot of info regarding my problem here: http://forum.allaboutcircuits.com/threa ... ir.128825/


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