How much will this repair cost me?

eyeprod · June 12, 2012, 08:23:54 PM

Played a show on saturday. I smelled burning (vintage 70's) pcb and saw smoke. Then the sound fizzled out. I opened it up and here's what I saw. Not cool, but doesn't look too expensive to fix. That is, if nothing expensive got damaged during this event. I did keep playing and tried turning up the volume as it fizzled out to zero volume (approx. 5 seconds). Another score for the Sunn backup head saving the day.

Any ideas?

I guess I'm mainly wondering if it looks like any really expensive damage was obviously done. I only see a burn-tout section of pcb, so I'm thinking maybe a new cap or two and possibly a tube? I see the wires going to two of the power tubes. I noticed nothing unusual about the tubes during this event. The smoke was all from the pcb, apparently.

The Shocker · June 12, 2012, 09:35:27 PM

In due to curiosity.

VOLVO))) · June 12, 2012, 10:11:41 PM

Depends on what did the cooking, Is this your V4?

eyeprod · June 13, 2012, 12:31:28 AM

yes, the v4.

This place I played at has supposedly damaged some gear in the past, though I have played there many times and never had any issues. Funny thing is, my sunn powered mixer also got cooked that night and I still have not opened that up, but the smell was exactly the same (burnt pcb) and it never died out. I turned it off as soon as I realized it as smoking, but I'm sure it needs looking at.

That's right, two smoking devices on stage in one set. People are still talking about it.

Mr. Foxen · June 13, 2012, 04:31:17 AM

If the place has dodge electrics, risking more than your gear playing there. Something will have burnt up the PCB, probably a resistor, and in turn, something will have pulled too much current through the resistor.

jibberish · June 13, 2012, 04:56:30 PM

yes, somehow you have to see what really happened to cause the burn.

im ignorant, but can you get the pin numbers of the tube socekts and id the tubes. maybe our wizards can piece together just what was between those 2 tubes, depending upon what they are.

from my limited studies, i can start to tell, based on the tube, sort of where things line up, and what to expect between tubes, like the tone stack or volume pot etc

also, we have no clue what burned up on the other side(probably a resistor, but it would be nice to know which one in the schematic). you are only seeing the backside. that component could be a huge lead to the puzzle.

what exact model amp is it. maybe everyone knows already(except for me), but you could pull the schematics.

i think between the schematics and an exact id of the burnt component(IF there is one even), maybe some guesses could start to be made

shorted caps pull huge current since they are supposed to be a total wall to DC when they are working correctly. that's my guess based on no specific info and assuming a component burned up(which i absolutely would not commit to saying at this point since i cannot yet see any evidence of a burnt component just from this pic. i only see a burn-thru from the other side so far).

second guess could be a mechanical short like dust and beer across two hi voltage traces if there is no apparent component involved, <-and im saying this, becasue if you look at the little yellow component codes on the backside of the pcb, you will notice that most are vertical mounted in the picture. only some diodes up higher seem horizontal. i dont really see any traces of yellow horizontal component id'er where that burn is, so ya we do need to know what is going on , on the other side. if those are the power wires for the 2 push pull tubes, well there you go.

jibberish · June 13, 2012, 05:07:40 PM

btw, the general soldering technique used on that pcb assembly looks marginal at best. i would look over all the wires and solder joints too just for shits n grins.. and inspect nearby wires and componenst for damage and possible replacement. insulation turns to ritz crackers when overheated, even if it didnt burn off at accident time, replace all those too.

jibberish · June 13, 2012, 05:11:13 PM

regarding squrrely voltages: undervoltage is deadly to equipment.
It forces bigger currents or unpredictable grey zone functioning with unpredictable results.

VOLVO))) · June 13, 2012, 05:39:15 PM

Right Clicky - View Imagey to enlarge

GREAT RESOURCE! http://www.ampegv4.com/

eyeprod · June 13, 2012, 07:21:23 PM

thanks dudes. I'll be taking it to my tech asap anyway, but just thought maybe it would be obviously bad or not so bad from the pic.

I'll keep ya posted

jibberish · June 14, 2012, 03:09:41 AM

sunno, that IS a great site thx.

ok im just playing nub general sherlock holmes tech here. let us know what the problem actually ended up being. i would love to know if i was even in the ballpark on my guessing.

and here are some observations from the schematic and zero feel for teching these amps.

a) not anywhere near the power amp section. all the power amp resistors are 3 digit. these are 2 digit near the burn..look like 3x or 4x...also.
b) those are smaller tube sockets, which generally isnt the power section either
c) im guessing something involving the V5 in the reverb unit or the main circuit funky midrange.
edit: d) failed coupling cap between V4 and the V5 stages OR that c21? heading to the output jack. (backup guess)
lol, ok now we wait.

OH! can you tell me what resistor numbers are of those two attached to the burned terminals? i cant see exactly from the pic(if it isnt already gone to the shop) thx for playing along with my game.

eyeprod · June 14, 2012, 07:25:00 PM

I forgot to mention that there's an original schem for my amp glued on the inner chassis lid. It's different than the one posted. I just noticed that it's dated revision F 1/22/74.

The burn is at R46 and R40 at the end the leads to the power tubes. R40 leads to V7 tube. R46 to V6. The other end they share.

jibberish · June 15, 2012, 03:17:26 AM

thx, im glad u did that for me.

i thought those looked like 4's on those resistor numbers, but of course none of that matches sunno's schematic...so i guess game is over...maybe i can find that rev schematic somewhere. or maybe dunwich has the foldout pinup PCB bunny of the month for that hawt schematic right over his bed.

your schematic in the case may have some value if it isnt commonly posted somewhere. i mean value to be scanned and hosted somewhere for the knowledge pool....

eyeprod · June 15, 2012, 12:35:24 PM

Ill try scanning it, but would look around for it online first.

I'm going out of town next week for 10 days so it will have to wait.

everdrone · June 15, 2012, 07:09:17 PM

thats scary dude, sorry to hear it!

those ampeg v4s are killer, I was on the old board and was digging your tone back then too, this reminds me when I was thinking about getting an ampeg v2... issues with these but I bet it served you well till now... they might know on the ampeg v4 forum: http://www.ampegv4.com/forum/viewforum.php?id=1

vintage gear kinda scares me cause all of the sudden the tech is charging you $400 for tubes and $300 for repairs...

I see lots of ampeg v4 issues: http://www.ampegv4.com/forum/search.php?search_id=1029118525

forumites there say Most amp repairmen don't know ampegs. They know fenders and marshalls, and these are really a whole different animal.

http://www.ampegv4.com/forum/viewtopic.php?id=1530

my marshall jcm900 scares me too tho

eyeprod · June 15, 2012, 08:09:44 PM

ha, yeah I hear ya. My tech guy knows fenders really well, and he's actually told me what you said about repairmen, near verbatim. He's solid though, so I think he'll be able to fix this. And he'll straight up tell me if he doesn't want to do it, which would be worse case scenario.

Thanks again for the good vibes, all.

everdrone · June 15, 2012, 08:27:30 PM

cool brutha, good luck

very cool amp, great to hear you using it, hopefully it is something small. I just bought this for $350 when it was on sale, I wanna protect my amp, does not protect against everything but furman can do some good with their power conditioners: http://www.musiciansfriend.com/accessories/furman-p-1800-pf-power-conditioner

eyeprod · June 15, 2012, 08:34:00 PM

I was thinking the same thing when my stuff burnt......power conditioner

jibberish · June 18, 2012, 05:45:52 AM

i wonder since most amps have to linearly step up voltage lets say 4x, would a slight overvoltage cause trouble? every 10% overvoltage would be roughly another 40v DC to the tubes and coupling caps.

the good thing is, the giant inductance of a power transformer is an awesome low pass filter that absolutely will not let a power spike through. so surge/spike protection(IMO) is a useless precaution, but power conditioning to keep steady state levels within tolerance could be useful.

too bad so much solid state stuff now is made 80-250VAC 50-60hZ for USA and euro use. that stuff is immune to any power crap, especially when you make an additional clamping circuit to shunt massive overvoltage to somewhere else, cant even blow it up then.

i still think undervoltage is the nasty circuit killer. as voltages drop, things tend to pull more current to maintain power

i really really cant wait to find out what happened. like a little kid heh.

[now i gotta get busy on blinky skull eyeballs heh, wtf, why not....]

Mr. Foxen · June 18, 2012, 07:25:33 PM

Power conditioners won't do much for you, and in some circumstances can make things for amps worse (there's buncha stuff from proper amp designers on talkbass) uninterruptable power supply is the actual thing you need to stop under voltage and those are expensive. 'Power conditioner' tends to be glorified power strip maybe with an RCD.

Basically, a correctly functioning amp sorts its own power out, it has power filtering and rectification and a transformer, adding more of those things won't help. If you amp isn't working, it needs fixing, not new things added.