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cavalli cth resistor smoking / burning up

post #1 of 15
Thread Starter 
Hi guys. I have been having some issue with my CTH, its the original board, not rev a. When I power it up, R16R starts smoking, I did replace that, and also replaced Q8R (just because it was near and I had a spare), but problem persists. Any idea what can be causing this? Thanks in advance for any tips troubleshooting this.
post #2 of 15

You posted this to the correct thread ("A Very...") & I saw it & meant to ask obvious questions like:  

Did this CTH ever work properly?  

If so then any ideas what could have brought the problem on?

Problems like you are describing are often from shorts somewhere (possibly even shorting the output).   Or misplaced / incorrectly installed parts.

You'll want to follow CTH debug/diag steps (maybe in my sig, otherwise in CTH threads).  Here's some links about CTH smoke from the past:

http://www.head-fi.org/t/542279/the-cth-compact-tube-hybrid-rev-a-thread/420#post_8241355

http://www.head-fi.org/t/542279/the-cth-compact-tube-hybrid-rev-a-thread/165#post_7479925

http://www.head-fi.org/t/398839/a-very-compact-hybrid-amp/915#post_5635805

post #3 of 15
Thread Starter 
It wad working fine at one point. Thedid something stupid, shorted inputs and maybe power to the chasis ground. After that it worked but e12 would trip at loud volumes, it was pretty unstable in general. It started smoking when I took it out of the Hammond case. I have looked through it for shorts but couldn't find anything. I do have enough transistors to replace them all, should I just go ahead with that? My fear is the problem is elsewhere and I might damage newly installed parts. Sorry if I shouldn't have started this thread, just wasn't sure if all the regulars had stopped visiting the old cth thread and wanted to open it up to more people.

Thanks!
post #4 of 15
Hey, no problem with the new thread & trying to get more input.
The CTH is a complex little beast but some have been able to narrow down the sand replaced for a burning episode (search CTH threads for burn, smoke ?). The couple times I tried replacing a couple/few TO92s in a CTH rail splitter or buffer it didn't work, the couple/few new parts smoked. So I went more or less a shotgun approach to sand replacement the time I had the problem. Search for posts by me & the text shotgun will find related info.
Edited by cfcubed - 1/15/14 at 6:18pm
post #5 of 15
Thread Starter 
what do you mean by sand rereplacement?
post #6 of 15
Sand=transistor(s)
post #7 of 15
Thread Starter 
Ah I see. Well I do have spare trnasistors for this build so I think this weekend I will replace them all.
post #8 of 15

Yes, sorry, as Nikongod said I used the slang "sand" to refer to semiconductors (as in sand->quartz->silicon dioxide->semiconductors).  So I meant for it to mean transistors (TO92s in CTH) and devices made up of transistors (its opamps & CRDs).  Note the CRDs are uncommon & expensive & don't think they've ever been the source of these problems.

 

So the shotgun approach for smoke in CTH's output buffer would entail checking the resistors & replacing the TO92s + opamp in this schematic:

http://cavalliaudio.com/diy/cth/main.php?page=schematics/opschematic

Limiting to problem channel may work.

Notes:

*  this is not the smartest path to repair - a smarter one would involve understanding the schematics & operation then taking measurements to determine the fault.  BUT taking measurements on CompactTH while powered up is very risky WRT shorting.

*  the events you say caused the problem are serious & may have taken out other CTH circuits (e.g. others off SCHEMATICS link here: http://cavalliaudio.com/diy/cth/main.php?page=overview )

post #9 of 15
Thread Starter 
Yeah I know it's not the smartest way to do it, but I am not advanced enough to figure out what might cause the resistor to smoke by reading a schematic. I already swapped most every to92, was good fun pulling them all out smily_headphones1.gif. Just didn't have five of them, including the rail splitter (ic2s), also ordered another ich and icp just in case. Hoping its not one of the opamps. Guessing it's not very likely that it's caused by a resistor/cap/diode.

I would also do some measurements, bit since turning it on causes r16r to burn up... And I don't know what effects I would see if I took r16 out either. So just went for ye old replace parts until it works, anything to get it back up, have such nice tubes for it, a shame to just let it sit broken, gathering dust.
post #10 of 15
Quote:
Originally Posted by arteom View Post
Yeah I know it's not the smartest way to do it, but I am not advanced enough to figure out what might cause the resistor to smoke by reading a schematic.

Me neither apparently as the time or two I tried it didn't work so I went shotgun to fix it.  And I helped design the thing:)

 

Again the CTH is quite complex, accomplishing a lot in its small, through-hole space.  And there is of course interdependency between some of its sub circuits that can make repairs like this difficult.

post #11 of 15
Thread Starter 
Quote:
Originally Posted by cfcubed View Post

Me neither apparently as the time or two I tried it didn't work so I went shotgun to fix it.  And I helped design the thing:)



Again the CTH is quite complex, accomplishing a lot in its small, through-hole space.  And there is of course interdependency between some of its sub circuits that can make repairs like this difficult.

Dang, I guess that speaks for its complexity. Well hopefully the parts I ordered come in early this week. I will replace the few transistors left, the icp and ich, will let you know how it goes.
post #12 of 15
Thread Starter 

It lives!! :veryevil:

 

Last night the last of the to92's came in, five pieces. I popped them in, cleaned the board top and bottom with isopropyl using a toothbrush. Powered her up, no smoke! Popped in a tube, led went green in good time. Cased her up, tested with some dispensable zune in ears, there was sound :cool:. I left it running for a bit, still no smoke. Tried my ath-esw9's, much better. There was some glare in the upper midrange, at this point it was past midnight so I plugged the zune in ears back in and left it playing overnight for burn in. Checked it this morning very briefly before I had to head off to work, sounded much better. 

 

Thanks for the help/encouragement cfcubed and nikongod. Honestly was dreading pulling out all the to92 and cleaning out old solder, but as anyone who has heard this beauty of an amp knows, it was well worth it. I think I am going to get a tkd volume pot for this guy. Aalso re-do the case, currently I have the power and heater switches on the front, want to moved those to the back of the case.

post #13 of 15

Victory!

post #14 of 15
Thread Starter 

Hey guys, new problem. While I was rewiring the amp I seem to have damaged the through hole IG (input ground), the bottom ring came off. I did try to connect the IG wire going to the pot to the top. But I am getting a buzzing noise, the noise does go away if I touch the G pins of the voluem pot. I am trying to wire in a TKD CP601 pot, I have followed the wiring diagram of it posted on parts connexion here http://www.partsconnexion.com/controls_pot_tkd.html (I have IG connected to both ground pins, and each pin going out to ground of output rca). Any tips on alternative wiring for IG? I looked on cavalli site, hoping to see where the IG goes, but it does go anywhere it seems..  

post #15 of 15
IG = SG = ground plane on CTH boards. Tie to SG if easy otherwise a ground plane contact near IG.
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