MRV-T500 internal clicking noise problem

[Beerad]

Hi diyaudio ppl, I'm a noob here and also to repairing amps... so please excuse me and my ignorance. I have a few alpines that need repaired and I'm pretty sure I'm competent enough to do it so yeah. I've actually learned quite a bit from lurking around here in just the past day or so from Perry and jol50. Awesome, thank you... I'm pretty sure I could get an MRV-1000(a couple fried fets) and MRV-100M(burned ground band and a fried fet) going from what I've read. Thank you bunches!! Perhaps I could get a little guidance when I finally jump into that? It'd be soooo greatly appreciated.

Anyhow, I'd like to start with this MRV-T500 I just bought on ebay advertised as 100% functional. It does work indeed but it has this really loud clicking noise as soon as you power it up and every few seconds or so. If the amp is pushed it could change the frequency of the clicks or make them go away but only for a moment longer than usual. I tried this connected to a different sub and power supply and still the same thing. Though this time it started cutting out. Amp was still on but just the audio going out. At first I thought it was since it was warming up... but when it wasn't working I hardly touched it and it started again. In this location it was sitting on top the sub and exposed to more vibration than before. Stopped again, tapped it... and it started playing again. The clicking in it is actually quite loud... seems like it would have to be something physical. I felt around a bit while it was on with the cover off and it seems to be coming from the power supply.

So, I'm guessing this is just a bad connection somewhere? Bad ground? I've done a lot of searching and couldn't find a similar problem with all the clicking. Took it completely apart and looked at the back of the board and everything looked fine but I know it's sometimes hard to tell if a joint is bad visually. I own several other MRV series amps including two other mrv-t500s which were in the same location I tested this one so I'm pretty it's not me at fault. lol Any help or input would be greatly appreciated! Thank you and thanks again for the awesome forum!

[Perry Babin]

You may have to gently push on various points on the board to see if you can narrow the area where the connection is intermittent.

Do both channel pop?

[Beerad]

Sorry... "power supply" probably wasn't specific enough. Attached an image of the part that seems to be making the clicking... the big square thing whatever it is... heh

[Beerad]

Doh, I probably should have checked that already huh? I've only tried it in mono but it sounded flawless until it intermittently cut out completely. No poping or anything, just good clean bass as it should have been...

[Perry Babin]

That's an inductor. It may be shorted internally but it's also possible that the amp is producing transients on the input and that's causing the inductor to produce the clicking.

[Beerad]

Thank you for the replies Perry. I was about to break apart a working MRV-T500 and start comparing things with the multimeter but first I thought I'd have another look at the one with the issue and I think I found the problem... a little crack on the board. I looked over it forever before I noticed it since most of my attention was around the inductor and this was on the opposite side. Posted some pics... sorry they kinda suck. Any suggestions on how to fix? Thanks!!

[Beerad]

I do have the soldering experience btw... I'm guessing I just need to bridge the highlighted points with some wire?

[richie00boy]

Scrape the coating away and tin the track, then lay some bare wire over it and solder in place.

[Beerad]

Hmmm, good idea... thanks Richie

[Perry Babin]

Yes. Any time there is a crack, you must bridge it with wire. Simply bridging it with solder won't be reliable.

If the board isn't fiberglass and actually has a crack, the ends of the crack may have to be drilled to prevent it from running (which would cause other traces to break).