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Old 27th March 2015, 11:04 PM   #1
zacster is offline zacster  United States
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Default Tried fixing my Creek 4240 amp but...

After reading this thread: Repair help requested - Creek 4240SE I gave it a shot.

Well it didn't work after replacing all the transistors. One of the bridge diodes, or maybe the small cap next to it, started to smoke. The transformer heated up too. This happened even after I pulled the internal fuses between the power supply and the amp section. In the schematic it shows the fuses between the tranny and the bridge, but in reality the fuses are after the big caps.

I'm calling it a day for now. The only thought I have is to pull the transformer output leads off the circuit board and then see, and read the voltage there. That doesn't tell me much except that the transformer works. Maybe I'll replace all the PS section since it isn't that many parts. The electrolytics were replacements that I tried as an attempt in the past to fix this amp, so they haven't ever been in use.

Any other ideas out there?
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Old 27th March 2015, 11:36 PM   #2
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Are the replacement 6800uF capacitors around the correct way?
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Old 28th March 2015, 12:09 AM   #3
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I would also check the bridge diodes.
If one or more have gone short it will take loads of current and cook the transformer.
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Old 28th March 2015, 01:36 AM   #4
zacster is offline zacster  United States
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I'm thinking the bridge diodes myself. The 6800uf caps are in the right way.

Another Mouser order I guess, I'll get replacements for everything else in the power section too, and hopefully it hasn't cooked the transformer.
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Old 28th March 2015, 01:38 AM   #5
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Quote:
Originally Posted by zacster View Post
I'm thinking the bridge diodes myself. The 6800uf caps are in the right way.

Another Mouser order I guess, I'll get replacements for everything else in the power section too, and hopefully it hasn't cooked the transformer.
Its nice to be sure what the problem was.
Check the diodes with a multi-meter.
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Old 28th March 2015, 01:46 AM   #6
zacster is offline zacster  United States
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I was going to do that. The transistors I tested after I pulled them all came up bad, so something really fried this thing. And just to check I was doing it correctly I tested a few new transistors and they all came up good.

I'm going to check the output from the transformer too, it should be 25vac.

And if all this fails, I'm thinking I'll just wire in a 3116 or something like it and use the switches, jacks etc... Or even a better idea, finally put my Aikido into a real box. I'm pretty sure I can isolate the pre-amp traces from the power section on the board. And the funny thing is that the Creek phono-pre add-on that I had installed in the 4240 ended up as the phono section of my Aikido. I could put it back into its original slot.

Last edited by zacster; 28th March 2015 at 01:53 AM.
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Old 28th March 2015, 03:59 PM   #7
zacster is offline zacster  United States
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So what I've found today...

First, I pulled the diodes and checked them. 3 of them seem to be good, with resistance/open in the proper direction and the diode check showing .4v to .5v drop in voltage. My understanding is that meters can't check to the full .7v that they drop in use. The fourth one cracked when I pulled it, and this is the one that smoked yesterday, so I can't check it.

The transformer is putting out 26vac from the leads, which is only slightly above the 25vac spec. I assume that's OK, and could just be my main voltage being high.

I also pulled the electrolytics, the 6800uf ones, and my meter won't read these high values, although quite honestly I'm not sure if I'm doing it right anyway. I have some smaller value caps that I can check to see if I'm doing it right. And just to be clear, the negative marking on the cap should go to ground, correct, and the positive goes to the + on the board? I know that seems obvious but I just have to ask.

So at this point I'm thinking that either the one diode was bad, or that the one diode became bad from something downstream. I don't have 3amp diodes on hand so I will need to order some more. Where is the RatShack when you need them? They were always good for a part in a pinch, although I'd be the first to say I couldn't see how they stayed in business the last 5-10 years.
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