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Powerdoc

Dead HR-772: Capacitor and general help please

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I recently became a member of the Carver owners guild and the HR-772 I acquired was knowingly dead but I didn't pay much for it so I look at it as a learning experience.  In any case, a number of the electrolytics seem to have some brown "stuff" at their base and some of the nearby jumpers are corroded.  This appears on the bases of some but not all of these capacitors.  Is there some factory-installed sealant that this represents or leaking capacitors?  I have some pics but can't post yet.  

 

Also, any general help with problems that 772's have/get would be appreciated. 

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Welcome.jpg

 

Welcome to the "club!"

 

I can't offer a lot of electronic guidance - the experts will be along shortly, but I can tell you the "brown stuff" at the base of the caps may well only be the rather unpleasant glue they used during installation.  It could also, of course, also be where the caps have spewed out their guts, as you suggest.  The corroded jumpers are certainly a concern.

 

Can you give us an idea of how far things get?  Don't run it for long, of course, but what happens - any sound, doe it go into protect, or perhaps nothing at all?  That will help guide those who do know their stuff to help you.

 

Regardless, of my ramblings, there are lots of folks here who can help out.  Relax, and let us know a bit about yourself, your system, and your musical interests.  :)

 

 

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7 minutes ago, Powerdoc said:

some brown "stuff" at their base and some of the nearby jumpers are corroded.

Most instances that brown stuff is old glue used to support large or vulnerable caps. Kind of a PIA to clean off. Corrosion is likely caused by the leakage from a failed cap.

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Thanks for the info.  What bothered me about the brown stuff is that while I understand using on larger caps some of the smaller ones had it too even if they were mounted above the PCB which made me think it's leak; also I agree the corrosion is worrisome.  Right now the receiver is D.O.A. :  No lcd screen and just a yellow light at the on/off switch.  Will replace some of the caps tomorrow that looked questionable (thankyou solder-sucking iron!).  I then will check voltages (if I can find them in the manual). 

 

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Welcome to the Guild!

 

A few more posts, and you can post a picture of your 772, and those caps with the brown goo.  That would be the best way to get a good diagnosis of that issue.  There may be other issues.

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Reading more about glue vs leakage, most posters on other sites say it's likely glue but one poster mentioned that capacitors which appear to have lifted themselves off the board probably have leaked.  I noticed a number of these in the HR so I'll replace them.  I hope my parts guys are open on Sat'y!  I'll need to shrink some of my files to post the pics.  Again, thanks guys!

 

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Given the age of your caps, it's probably not a bad idea to be replacing them - if they haven't done a catastropic failure, there could well be one or more on the verge.

 

Good luck!  :D

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Hello Powerdoc, and welcome to thecarversite.com. We're glad you're hear. ;) There is a lot of information here, much technical know how, and a pretty good bunch of folks that are happy to help.

 

You should be able to post pictures now that you've reached Novice status. There's a link to Luna editor embedded in the "Insert other media" button. You can resize your photos there if you don't have a photo editor installed. 

 

When you get a chance, please consider uploading pics or your gear in the Members Systems area. We all like pics of all kinds of audio gear.

 

In the meantime, kick your shoes off, turn up the music, and welcome aboard.

 

giphy.gif

 

 

 

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1417896272_8120image1.thumb.jpg.e34ebe25f0038f222b09c14d68325af3.jpgWell now that I'm a novice (not in the Catholic sense as my fingers have been electrically violated many times!) I'll see if I can get the pics up.  I went ahead and replaced some of the questionable capacitors  today and noted 2 types of brown stuff:  One is sticky like dried airplane glue and impervious to 91% alcohol; the other is crusty and can be partially dissolved with alcohol and gently scraped; the former is only removable with a pair of pliers biting bits off.  The 2 purple caps in the foreground of the first picture are stuck to the circuit board and alcohol doesn't seem to be budging it.  I have a gallon or so of acetone so I'll hit it with that next and after that it may be hammer time.8,1,20 image1.jpg8.2.20 image2.jpgBTW:  Love that photo editor!516697701_8.2.20image2.thumb.jpg.4dca3fa7e7cfc98f9d3f57be0930b268.jpg

 

Edited by Powerdoc
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I've also looked at the voltages around the main transformer.  The power relay goes conducting for about 10 seconds then shuts down.  I assume this is a protection circuit.  Still nothing on the screen so I'll do some more digging.  And, if anyone has a secret formula for dissolving that pesky glue, I'm listening.  Thanks guys (and gals if there are any here.)

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Welcome to the site. You shouldn't have any problem getting that up and running with the plethora of knowledge available to you. 

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Is there a better forum to ask questions about the HR-772 for electrical problems?  I guess what I need now is information about what usually causes protection mode in these amps?  There doesn't seem to be a section about Carver receivers that aren't HT receivers

 

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17 minutes ago, Powerdoc said:

1cm spacing radial leads; saw some snap-in's but nothing with radial, solder leads

Use a capacitor with larger capacitance in the circuit if it will physically fit on the board. If it’s in the power supply, a larger capacitor won’t cause issues.

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Realizing that, I looked.  voltage is the problem.  Has anyone used a snap-in and had the leads long enough to solder in?

 

Edited by Powerdoc
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Yes. I use snap ins. Just make sure you have enough room. In the MXR's you have to go with the same diameter power caps because of the area limitations. And the lug spacing is important unless you want to drill the PCB. You can go higher on the voltage and temp. 

 

I use snap ins for the power supply caps and radial for the other smaller caps.

 

I haven't had any problems with Mouser when I order caps. They have had everything I need. Referred by @Nahash5150

Edited by Rob
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If you are looking for the big power caps I have these that I am not using. 10 mm lug spacing 35 mm diameter. 63v 10,000uf.

 

But I only have 2 of them. I can't see the voltage on yours.

IMG_5120.JPG

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Am going to get a snap-in locally and see if it fits.  The spacing looks ok but the termination looks like it's too wide for the circuit board.

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9 hours ago, Rob said:

If you are looking for the big power caps I have these that I am not using. 10 mm lug spacing 35 mm diameter. 63v 10,000uf.

 

9 hours ago, Powerdoc said:

Am going to get a snap-in locally and see if it fits.  The spacing looks ok but the termination looks like it's too wide for the circuit board.

But I only have 2 of them. I can't see the voltage on yours.

IMG_5120.JPG

 

The spec for the capacitor is 80v. thanks though!

 

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14 hours ago, Powerdoc said:

Is there a better forum to ask questions about the HR-772 for electrical problems?  I guess what I need now is information about what usually causes protection mode in these amps?  There doesn't seem to be a section about Carver receivers that aren't HT receivers

 

Replace all of the electrolytics in that power supply section. If you really want to keep it for longer-term use replace all of the electrolytics period. Once you have those replaced you should end up with a functioning power supply - you need that to troubleshoot any other issues.

 

If it were mine I would not power it up again until all of the caps had been refreshed and I had done some basic checking of the output stages.

 

If you find another Carver forum out there that has competent tech support please let us know !!!

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Thanks.  My intention as you stated is not to power up 'til I can get the new filter caps. I didn't mean to look for another web site, I was looking for forums in this site; there doesn't seem to be one just for the receivers.

 

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The diameter and lead spacing of the originals will narrow down your search. I use small digital calipers to measure. Snap-in vs leaded is not such a big deal as long as you prep (clean off old solder) the board and in some cases enlarge the holes slightly. If the through holes are clean of snags and large enough to accept the cap terminals, snap-in fit securely with enough material protruding for good solder connection and without damaging the pads. 2 sided/multi layer boards have a tiny sleeve in the holes to connect the various traces that require care is taken to maintain those connections. I believe you are NOT working with that style and yours is a standard single sided board.

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