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Thaddeus Smith

Swapping out filter caps

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The filter caps on my ATI AT1505 are degraded and failing. What sort of headache am I embracing if I were to try and swap them out on my own? I'm comfortable with soldering and have done small T-Amp projects in the past.

 

I've done a fair amount of troubleshooting on my own and with ATI support directly and we've isolated the issue with a bit of certainty. I contacted a local repair guy and he was hesitant to touch it without schematics in hand (ATI says the CEO might have it somewhere on an old PC at home, but not with any certainty). Then he wants to charge bench time to investigate, can't quote parts without seeing what's in there, and won't guarantee that it fixes my issue - all fair points. It's a 75lb amp and I don't want to be lugging it all around town for just a random look-see... so in my head it's just a matter of pulling the amp modules, identifying the caps in place, ordering caps, and soldering the new ones into place. I can do that.

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Have you been inside the amp? Sometimes(most times) the big filter caps are pretty easy to replace. Just held in mechanically and then connected to with screw in terminals. Now if you want to replace all the filter bypass caps on the circuit boards that will get more involved but if you can solder you can do it. And you have the time of course, I know we're all busy.

Tell ATI you would really like to have the schematics if at all possible.

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Found Owners "Guide" at HiFi Engine but no schematics:(

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21 minutes ago, babadono said:

Have you been inside the amp?

Exactly.  These aren't laid out like a conventional amp and are hard to get around in. 

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2 hours ago, CECAA850 said:

These aren't laid out like a conventional amp and are hard to get around in.

 

Looking at a picture, it appears to be a modular design that could be easy to unbolt (maybe) and then have good access to the caps. 

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2 hours ago, CECAA850 said:

Exactly.  These aren't laid out like a conventional amp and are hard to get around in. 

 

I haven't yet cracked it open. I don't mind paying a guy, and I recognize the expertise that goes into repairing electronics. But I'm also not completely incompetent, so I'm tempted to try...

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2 hours ago, babadono said:

Found Owners "Guide" at HiFi Engine but no schematics:(

 

Yeah, I've got that PDF as well.

 

 

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Go for it.  You'll want to ensure the caps are discharged.  It's not entirely unusual to have discharged your supply filter caps and find later that they're not discharged (some voltage magically re-appears), so just be aware of that.  You should be okay if you've done anything similar before.

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7 hours ago, Thaddeus Smith said:

The filter caps on my ATI AT1505 are degraded and failing.

 

What symptoms led you to this conclusion?

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4 hours ago, Thaddeus Smith said:

But I'm also not completely incompetent,

Who told you that?

  • Haha 1

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24 minutes ago, jimjimbo said:

Who told you that?

Goat castrating, chicken plucking, capacitor swapping, yea its all pretty much the same:)

  • Like 1
  • Haha 1

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3 hours ago, glens said:

 

What symptoms led you to this conclusion?

 

It's not all channels, and not all the time - mostly when the amp has been powered off for a while and then is powered back on. It's not a ground loop. Nor is it mechanical hum from DC offset. I purchased an Emotiva CMX-2 and it had no impact on the noise within the speaker: https://emotiva.com/products/cmx-2. Here's the email thread with ATI support (chronologically backwards)

 

 

Quote

 

Apologies for the late reply; Fridays are a short day for us so I missed your e-mail. The caps are easy to identify. The amp is so old that we don't have schematics for it in our database (I searched). I checked with the owner and he said that he might have schematics on one of his computers at home. If the repair shop really needs them, then I can have the owner look through his old PCs. 

 

Best,
Sanjay

 

 

On Fri, Dec 7, 2018 at 12:28 PM  wrote:

I was able to replicate the humming again this morning, and it once again disappeared. I was having trouble discerning much difference in loudness or time between the center input and sides. Ultimately, it does go away and then the amp is completely quiet (until media is played back).

 

I’ll search out a repair shop. Are the filter caps easily identified, or will they need to reach out for a schematic?

 

Regards - Michael

 

From: Sanjay Durani
Sent: Thursday, December 6, 2018 4:40 PM
To:
Subject: Re: AT1505

 

 

The amp is warmest at the middle and gets less warm towards the sides. That means the caps on the middle amp module are drier, getting less dry as you work your way towards the outer modules. Was just checking if that's how it is with your 1505, because it would confirm the probable cause of the initial hum.

 

Since it is just a dumb amp (no DSPs or software built in), any competent electronics repair shop should be able to service it. First have them check the filter capacitors; the ones starting to dry up can be replaced by caps with the same values.

 

Best,

Sanjay

 

 

On Thu, Dec 6, 2018 at 9:50 AM Michael Ray wrote:

I did try all modules and found them to be the quietest, but I'll test again tonight and specifically check for any warm up time on the two outermost modules.  

 

At this point it's a minor annoyance, and I mostly want to be sure that there aren't any electrical concerns. If it's something that can be repaired, what are my options for an amp of this vintage? I'm in the Dallas metroplex, so I figure a local solution is most prudent, given the weight of this device.

 

 

Cheers - Michael

 

 

On Thu, Dec 6, 2018 at 11:43 AM -0600, "" <noreply@jotform.com> wrote:

 

Thank you for contacting us. Sorry to hear about the problem. From your description, it appears to be old filter capacitors that are taking time to warm up (called "forming"). If the amp had previously been installed in a warm place without adequate ventilation, then the caps would have started to dry out, resulting in 30-45 seconds to properly form.

If you connect your speakers to the two amp modules farthest out from the centre of the amp, does it still take 30-45 seconds for the humming to fade away?

 

Best,
Sanjay Durani
Amplifier Technologies Inc.
ATI-B&K-BGW-Datasat-Theta Digital






On 2018-12-05 20:58:12,  submitted:

·  Submission Date

2018-12-05 20:58:12

·  Your Name

Michael Ray

·  Your E-mail Address

 

·  Your Message

I just brought home an older 1505 that I purchased used. I'm waiting for interconnects and so I only have 2 of 5 channels hooked up tonight.
Everything powers up fine, all channels work, fuses are good, and no warning lights. When first powered on, I get about 30-45 seconds of hum through my mains (Klipsch La Scala) - sounds just like a ground loop - but then it fades away and the channels are quiet. I hear a slight hum with my ears directly on the tweeter horn, but that's to be expected with my high sensitivity speakers.
I'm just curious if the initial hum that fades out is normal behavior or something I need to be concerned about and have serviced.
Thanks! - Michael

 

 

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I loathe emails/threads were new material gets inserted above the old, in reverse order!

 

They're going to be large electrolytics with high values.  Easy to spot.  There'll be at least one each between + and ground and - and ground.  This whole paragraph is under the proviso of "usually."

 

If you like the amp and intend to keep it, hit them up for the schematic they've offered. 

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Thanks for the feedback guys. August is a bit full already, but I may dig into this next month and see what I can figure out. If able to easily remove a module I'll post up some pics for feedback.

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10 hours ago, glens said:

If you like the amp and intend to keep it, hit them up for the schematic they've offered. 

Seriously. Pester them to get it.

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Most likely. Those are probably the main filter caps on the rails. There are no other big caps by the toroid in the front? Is there another "twin" cap on each board maybe down near the bottom of each card?

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2 minutes ago, babadono said:

Most likely. Those are probably the main filter caps on the rails. There are no other big caps by the toroid in the front? Is there another "twin" cap on each board maybe down near the bottom of each card?

 

 

Dunno, all conjecture at this point since it's hard to find pictures of the internals. I'll just dig in and document as best as I can.

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If I were going to dig into one of these as deep as you're contemplating I would replace ALL the electrolytic bypass and coupling caps as well as the main filter caps. I would use non polar electrolytics for the coupling caps(probably Nichicon Muse series). But that's just me, I'm anal about this kind of stuff.

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