Denon AVR-485 Repair - diyAudio
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Old 29th October 2014, 03:23 PM   #1
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Default Denon AVR-485 Repair

Okay so I'm hoping this is the right place to post this..

I received a Denon AVR-485 from a friend, in non-working condition. It had a power supply Issue, and I believe the amps were done for as well. I decided to try to rebuild it, as everything else worked. I managed to find the service manual for this thing, and I tell you.. I don't understand why they did some of the things they did..

After going through all the board schematics I found I needed a -33v supply for the screen, a 24v supply for the relays, and this feeds a 12v regulator. Dual 15v rails for the audio input board, and various other things. A 5.6v supply for the CPU board, and finally a 5v supply for the DSP board..

Okay so the -33v can be from Vdd to like -45 on an LC75725 (the one in this receiver is a LC75721, but couldn't find a datasheet) so I can get away with -24v. They used a zener diode/transistor supply for that in the receiver. The 5.6v rail came from a 5v regulator, with some shutdown circuitry, but we dont need that. I knew what I needed and got to work.

The 5.6v supply comes from a small aux transformer, and is powered on when the main switch on the front panel is pushed. This sends the 5.6v to the CPU board, and if there are no faults detected that sends a signal to a relay which turns on the main transformer. It then runs a self test, and turns all the relays on if it passes.

I have dual 24v rails, dual 15v rails, 5.6v rail, and a 5v rail.. all on this little board that measures 141mm long by 74mm wide by 65mm tall. The height might get reduced if cutting the heatsink down is permissible, have yet to test the thermal dissipation of that heatsink.. The 15v regulators heatsink rises about 20 degrees, so things should be okay with them being that close to the caps (which are 105 degree rated) I need better caps for the 5v supply, and need to place a few more decoupling caps yet. Oh and add the connectors, waiting for them to arrive.

So, how do you guys think I did? I personally think I went too small, and didnt pay enough attention the layout.

The next step will be to wire it up in its final spot, and start working on the preamplifier boards, and getting some amplifier modules mounted on the heatsink. Updates to come
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Old 29th October 2014, 07:32 PM   #2
glen65 is offline glen65  United States
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So why aren't you using the original power supply board?
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Old 30th October 2014, 12:25 AM   #3
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The power supply was on the main board, which also contained all the amplifiers. Since I planned on replacing the power amps, I decided to rebuild the power supply board too. The power supply was spread all over the board, so I couldn't just cut it out and use it..
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Old 30th October 2014, 02:22 AM   #4
glen65 is offline glen65  United States
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I see, I didn't know you were going to replace the amps. I thought you were just repairing them.
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Old 30th October 2014, 02:44 AM   #5
srinath is offline srinath  United States
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ineedaname - You're my new hero.

Seriously I thought I was the only one getting into these HT amps to try to fix them.

I have not done this deep a job - I'll be watching this thread.

You're fixing it into its original design, or building a different amp in the chassis ?

Thanks.
Srinath.
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Old 30th October 2014, 12:56 PM   #6
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I want better amps in this thing, and I don't need 6 amps anyway.. That is just crazy.. I Will probably be doing something like LM3875 amps or something simple for now, until my budget allows for more (I already have a few of these amps laying around)

I have decided thought to rebuild the power supply, because I realize I should include some of the protection circuitry. I will be adding the power down circuit, and a couple things for the protection pin, nowhere near original though (they have like 5 things that can go wrong and trip it) I have ordered the parts so hopefully they will be here tomorrow, Digi-Key is usually pretty fast for me. Once I have the layout sketched up, I will post it and maybe you guys can help me find some errors. I got lucky on that first one, and it worked first time around. I will be winding my own transformer for the power supply too. (I have an old 25VA toroidal transformer laying around)

Here are some pics (the knob isn't missing, it's laying over there somewhere) Look at that heatsink, its beautiful!!! 278mm x 100mm x 46mm Guessing around .5C/W or so based on similar sized ones I found online.

Can you stack toroidal transformers, like one on top of the other?
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Old 30th October 2014, 05:13 PM   #7
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sorry, but from my point of view is wasting time.. This amp in mint condition i can buy for 50 USD... I think there is just one useful thing - heatsink :-)
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Old 30th October 2014, 06:15 PM   #8
glen65 is offline glen65  United States
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Quote:
Originally Posted by maxwell007 View Post
sorry, but from my point of view is wasting time.. This amp in mint condition i can buy for 50 USD... I think there is just one useful thing - heatsink :-)
Yes, but doesn't look like he's interested in the stock design. Since the amps are blown anyway, he's decided to use it for the base of a diy project.
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Old 30th October 2014, 06:30 PM   #9
glen65 is offline glen65  United States
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Quote:
Originally Posted by ineedaname View Post
Can you stack toroidal transformers, like one on top of the other?
Should be fine, make sure that they are both connected in phase with each other.
In other words make sure the same color wires on the primary are connected in parallel.
Also make sure there is a gap between the two for cooling. There are different ways you
could do this. But I would probably want to use rubber pads to space them, plus it would help dampen and any vibration between them.
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Old 30th October 2014, 07:49 PM   #10
srinath is offline srinath  United States
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Default heatsink and transformer

Quote:
Originally Posted by glen65 View Post
Yes, but doesn't look like he's interested in the stock design. Since the amps are blown anyway, he's decided to use it for the base of a diy project.
More than heatsink I think the transformer is what is worth the $$$.
I've picked up a few dead amps for 20 or less.
Cool.
Srinath.
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