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Post by tijiuanakez on Aug 13, 2012 6:25:52 GMT -5
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Post by tijiuanakez on Aug 13, 2012 8:56:16 GMT -5
Actually scratch the speaker not making any sound part. One of the speaker wires was disconnected. It now works on both channels but it fully of crazy humming and cracking and volume spikes.
Hopefully the cap should fix some or most of it.
Anyone see any problem using the caps I listed?
Thanks.
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Post by newey on Aug 13, 2012 10:32:18 GMT -5
tk- Sumgai is our resident amp guru, he'll be along in a while. I wouldn't venture a guess at your problems . . . I didn't know if you had seen the rather lengthy thread we had, started by cheezor, on his problems with the same amp. Several others jumped in on that thread with similar troubles: guitarnuts2.proboards.com/index.cgi?board=Amps&action=display&thread=2833It sounds like your problem is somewhat different, but in case you hadn't seen it, I though tthat thread might give you some insight. |
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Post by sumgai on Aug 13, 2012 11:20:30 GMT -5
sumgai is our resident amp guru, he'll be along in a while. I will be?  Did I get the memo?  Sure, I'll take that up..... kez, newey's correct, your problem isn't the same as what the other thread addresses. While you don't describe how you determined that a cap is blown, I'll take your word for it, at least for now. Deal is, if it's a power supply cap, then chances are excellent that: a) You've got a bit too much B+ (high voltage) on your tubes, and; b) You've got hum and other kinds of noises present at the speaker. You also probably can't control the volume, if any, of your guitar signal. But hopefully, once you heard all the crapola, you decided it's best to leave it off until everything is fixed.... good idea, 'cause wildly swinging AC on top of the B+ can cause several other component failures, none of them cheap to fix, and not all of them easy to find in the first place. Bad ju-ju, that.  As far as caps go, anything with the same value/rating will work. You can use a higher voltage rating, that's OK, but try to not go too much higher in the microfarads department - that can cause a lower B+, which in turn can affect the tone in a negative manner. Pretty much all brands are alike, so take yer pick. HTH sumgai |
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Post by tijiuanakez on Aug 13, 2012 18:22:46 GMT -5
Thanks for the replys guys. Yes I saw that other thread, actually thats how I found this site. Was going to post there but thought it was different enough for its own. sumgai, the symptoms you describe sound like what I'm hearing so I hope its just C32. (the top has popped out on one side) I took the liberty of ordering a set of EL84 power amp tubes aswell (matched quad sovtek) just incase. Like I said, If I take a line from the effects loop, the preamp sounds ok with no strange noises so I figured must be blown caps or power amp tubes. Let you know how I go!  |
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Post by sumgai on Aug 14, 2012 0:20:26 GMT -5
kez, I've seen caps "pop" like that many times over the years, and still work as they should. However, it's never a bad idea to replace something that looks like it's about to go South, even if it could've lasted for years longer. Sure as you-know-what, Mr. Murphy would bounce up and proclaim "Gotcha!", right as you fired up for that all-important audition for the Big Time.  While yer in there snoopin' around, take a close look at the resistors going to the screen grids..... they sometimes go bump in the night, but usually it's pretty obvious to the eye. (That's pin 9 as you look at the underside of the socket, and the value should be 100Ω at 2 watts.) Sometimes the wattage used was too small, and they overheated.  HTH, and GL! ;D sumgai |
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Post by tijiuanakez on Sept 13, 2012 17:38:50 GMT -5
Ok partial success. I replaced 4 of the 5 opto-isolators at random (because only counted and ordered 4 by accident), the suspect power cap, and the power tubes. Now the overdrive channel is working perfectly bar some gain pot noise, but I can't get the clean channel to work.
Seems likes its stuck on the lead channel. Channel switch isn't working it seems. I tried cleaning the footswitch jack and bridging the footswitch circuit but still stays on overdrive channel. Clean channel controls do nothing.
Reckon it could be that one last opto?
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Post by sumgai on Sept 13, 2012 18:03:27 GMT -5
Reckon it could be that one last opto? Yep. The panel switch and the footswitch both act upon the optoisolator, which then causes the circuit path to switch channels. In this case, I'd bet that the o/i is getting the switching instruction, but is not performing as it should. Of course, it's easy to test that - simply disconnect the o/i, and manually jumper the circuit to see if the amp operates as expected. Do this for each channel, just to be clear that you are getting the desired results. I'll leave out the usual High Voltage warnings, as you seem to have made it this far.... presumably by using all due care and caution. HTH sumgai |
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Post by tijiuanakez on Sept 16, 2012 23:58:34 GMT -5
Any chance you could elaborate a bit more on how that might be done?
I'm not sure I understand what you mean by i/o.
Thanks.
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Post by sumgai on Sept 17, 2012 1:50:42 GMT -5
Any chance you could elaborate a bit more on how that might be done?
I'm not sure I understand what you mean by i/o.
Thanks.That o/i, as it opto isolator. Sorry. I just reviewed the schematic for your amp, and I think that at this point, it's best not to mess around trying to do any jumpering. The way the amp was designed, it isn't supposed to have both channels on at the same time. (Dunno why, but that's what Crate wanted, so there it is.) Jumpering would be fruitless because we'd really just be turning on both channels at the same time. If you can't be sure that the Dirty channel is off, then there's no way to figure out if the Clean channel is even on at all. But not all is lost here!  You said that the Dirty channel works, and continues to work, even when you flick the switch. That tells me that there may be a bad connection to one of the switch transistors (that control the optoisolators), or else a bad transistor itself. That bad connection means that the -10vDC isn't getting to where it's supposed to be, for whatever reason - bad solder joint, broken trace on the board, etc. I'm assuming that you already have the schematic for your amp, but just in case..... I'm looking at this one: www.blueguitar.org/new/schem/misc_amp/crate_vc3112pre.gifNote the jack and associated circuitry (near the chart), and the nearby transistors. See those two Test Ponts, TP 10 and TP 11? Only one of those should be active at a time. Put your meter on them (one at a time (unless you have two meters!)), and take readings. Hint: Don't rely on your memory, even for a few seconds - write down what you measured! Flip the Channel switch, and take readings again. Now, just to be thorough, do the same for the Footswitch jack. (Err, assuming you do have the footswitch.  ) If those two Test Points are behaving correctly, then the problem almost surely lies with your last optoisolator, the one you have yet to replace. If they aren't working as they should, let me know, and I'll give you some more things to test. HTH sumgai |
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Post by tijiuanakez on Sept 20, 2012 18:51:07 GMT -5
Hmm.. after trying to find those test points I did find there actually was a problem with the footswitch jack. Now the channel switch engages and disengages the dirty channel but the clean channel doesn't engage at all.
I guess I'll just order some more opto isolators and swap that one out to be sure.
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Did I get the memo? 
)