C-91 Elite power up noise (PS Caps?)

[Ricktptman]

I've owned several C-91's over the years, and for the most part, they've aged very gracefully. This (my main system) preamp has developed a "whitish/pinkish" noise during the first three or four minutes of power up, in ONLY the Left Channel. I powered on the amps first to test them, and have ruled the amps out. (three Sunfire Signature 600's and a Cinema Grand.) It's definitely coming from the LC output, and only the LC output. I believe the preamp is a dual mono design. Has anyone ever had this problem with one of their C-91's? Is there a list of likely culprit "caps" to test? This thing is racked and stacked with caps, and I'm okay with replacing a few, but a total recap wouldn't be my first option. TIA for any help the ultra-techs here might be able to provide.

 

[calman46]

Maybe a cold solder joint . Have you checked the output cable & jacks. I would gave them all a good wiggle when you power up. Try to make it make the "whitish/pinkish" sound , wiggle some caps in that channel. I recapped my C-91 but it had problems, works nice now. I wouldn't try total recap without having a Hakko de-soldering gun or similar as the board traces where very thin on mine.

 

[whoaru99]

PS caps I'd say would be more likely a hum and I think not something that would go away after a few minutes.

 

[Ricktptman]

Thanks to everyone for your insights. Yes, the Hakko FR-301 wasn't optional for me when maintaining high-quality work. It's on a short list of tools that I wish I'd bought years ago. I found one shipped new from Japan at a very reasonable price back during one of the relatively recent economic crazy trains. (I should've acquired it years ago.) I will check for CSJ's. But the "noise" decreases in a way that made me think of a cap reforming. The problem with that is that it's used every day and doesn't sit for more than 12-24 hours without being powered up. As of today, I haven't heard it make any noise. We had some power outages here (SE, US, thanks Duke Energy) that knocked out a PS capacitor in my Marantz AV8802a AV preamp/surround half of my main system. The capacitor issue is well-documented on the Internet, which made it possible for me to rescue it. (I'll NEVER afford another one...) It also did something I still don't understand to the PS brick on my HP Laptop. It wasn't/didn't charge and ran the battery all the way down. I unplugged it and let both the laptop and PS brick sit for about a day, and (thank God), it worked as if nothing had happened. (I'm getting too old for this @#%^. Not really laughing out loud anymore...) I'll look into it. The C-91 is the nerve center of my main system, and it will NOT be a small job to install/uninstall. Thanks again for your advice, everyone!

 

[Ricktptman]

Update: I'm into the predecessor to my present 91 (same symptoms, I just found a replacement and couldn't work on it because I'd just had cataract surgery) and I see two values of suspect caps in the general area of the PS rectifier: 50V, 470uF with a third wire coming out of the top that appears to connect to the negative leg, but elsewhere on the circuit board. The second is a standard 50V, 330uF capacitor. There are four of each type. Can someone identify it? I don't want to order the wrong replacement. Would the go-to replacement be a UKL Nichicon? Here are a couple of photos. TIA, everyone...

 

[Ricktptman]

Update: I replaced the slightly swollen 50V, 330uF cap in older 91 #2 (pictured), and it yielded a slight improvement. I used a generic cap from an Amazon kit, as a test. DigiKey says the UKLs are delayed in shipment. (Huh? I never had that happen before...) I installed that generic Amazon kit cap to try to get a read on whether to cancel the Digikey order. Not sure what's up with that, except that virtually everything seems broken now. Google. Amazon. Utilities. (including Internet & Wireless...) I can't even get my HVAC replacement people to show up when they say they're going to show up. Maybe OT, but not really...at least from where I sit. Customer satisfaction has gone AWOL in my zip code. Concerning...

 

[Ricktptman]

Cap tested VERY bad using my Capacitor Wizard. At this point (whenever Digikey decides to ship my order, it's still not OTD), I'm going to replace all 8 of the 330uF/50V caps and see if that solves the problem. If not, I'll replace these oddball dual-negative lead (?) caps and hope for the best. I'm still looking for any helpful insights if anybody has recapped the PS's in one of these vastly underregarded preamps in the past. TIA...