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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: Re: The astronomical (relitvely) cost of repairs posted by ThomDP on April 21, 2007 at 12:23:59:
Dennis,No, I am quite sure Sparky is dead on. Bitter? doesn't sound like it to me. The shop where I was working regularly (notice the "was", it's been so slow the last 2 months there's almost no point in even going except once a week to see IF there's something to work on). Most places have a "diagnostic fee" or a "minimum service fee" that adds up to a half hour's labor cost, or around $30-40.
Does it take a half hour to find out what's wrong with something so it can be repaired? Only when you are REALLY lucky. In fact, it may be worth going and buying a lottery ticket the day it happens, because you're definitely on a roll!
For instance, if someone brings me a power amp that's "blowing fuses", do I stick a fuse back in there and throw the switch? That would be CRAZY. Step one, get continuity meter and check to see if in fact all or some of the fuses are blown (sometimes none of them are). If you find a blown fuse, step two is to figure out what that fuse protects. Main fuse? could be lots of things. Just one channel? make sure all the fuses for that channel are removed, power it up, and see if the other channel is good. Usually, you are keeping your fingers crossed that it is, because you can measure everything on the bad side, and compare it with the good side. But, before you declare a channel good, you have to take the meter and check to see if there is DC on the output. If there's a significant amount, and there are not huge coupling caps past the output transistors (assuming it's not tube), then both channels are effectively out. Step three? Completely disconnect, which at least means desolder, and sometimes remove totally, ALL the output transistors, on each bad channel. Draw diagram showing where each transistor came from, so you don't put one back in the wrong place. The "big amps" can have more than 6 pairs per side, 24 total or more. Step four? power the amp up, see if the fuses hold, check for signal and/or DC on the bases/gates of the output transistors. Signal good and no DC? you got lucky. Step five, check every output transistor for shorts/open junctions, HOPING that they are not MOSFETS, checking them reverse polarity also to make sure none are "leaking". Find a shorted or open transistor, but just one or two on each side? (by the way, suppose the amp came in at 9AM, wonder what time it is now?) Now, you could just replace the bad transistors, but you know that the others on that rail are probably stressed badly now, and it's better to change them all, because sending home a "ticking time bomb" is not going to be good if another one fails two days, or even two weeks or months later. Oh yes, before we call the owner with a repair estimate, we better check all the emitter resistors (assuming it has them) to make sure they are in spec, because a shorting transistor can cook one of those pretty quick. It would stink to put the whole amp back together, just to watch it go up in smoke again when you get to the testing phase.
next, you make a parts list to totall up what all is needed, hoping that the output transistors are cheap. $5.00 each (wholesale even) or more isn't uncommon, and if in fact it is safer to repalce say, all 24 in our ficticious amp, not counting emitter resistors, that's $120.00 just for parts! It just took you say, 3 hours (yeah right!, more like 4) to diagnose the problem, and you know replacing bad parts, reassembly, cleaning, and testing will take another 3 and a half hours (this isn't counting "burn in time" when we let it play to make sure everything's ok when it really gets warm). Hmmm, let me see, at $60 an hour labor, that comes to $450 labor, plus $120 parts, wow, we're up to $570! Now, you know the amp, even though it's nice, is only worth $200 at most, and so does the customer. Can you call with a $570 repair estimate? Duh, no way. Ok, blow off the almost 4 hours you already spent on it, where does that leave us? $330. Ok, that's not gonna work, Hmmm. Ok, charge for just 2 hours labor. Even though that's STILL $240, you call with the estimate.
Here's the part that really sucks . . . if the owner says "ok", you're going to work a total of 7 or more hours, but only get paid for two of them. Wait, you don't own the shop? Well, then you're not going to get all of that even. IF the owner says, "no", well, you just spent almost 4 hours on something that you are not going to get all of the $30 diagnostic fee for. Oh WAIT, the owner wants to come pick it up, and take it someplace else for a "second opinion". OK, better put it all back together, just like it was when it came in, which means resoldering, and cleaning up after yourself, and making sure you've really done it right so the next tech doesn't say, "Oh, those other guys TRASHED this thing". So, for seven hours, you just made $20!
Of course, you'll just say that I'm "bitter", and making stuff up. Well, bitter I don't know about, but yes, the above is a conglomerate of things that may happen, and it often does happen that way, so if you want to call it "made up" go ahead.
If you want to hear a REAL one, and I'll keep it short, I promise. Last week, at one of the places I do some work for, I get an Aragon power amp that was "blowing the main fuse". I go through all the steps above, but all the fuses are good. I guess the owner put a new main fuse in, it was a high-amperage ceramic one, not very common. So, start from the power supply out, because it was all easy to disconnect, power up to see if fuse holds, which it does, since I "got lucky" and all the outputs are socketed, I take them out, notice a small scorch mark on one, test each channel at a time, all's well. Test all the output transistors (only 8 total in this one), they're all ok. Huh? this doesn't make sense, maybe they just crossed speaker wires. Put it back together to test, remembered the scorch marked transistor (big TO3). Right where it belonged, there was a shielded signal wire with a melted spot through the insulation. YAY! I found it. Collector to ground? fuse go boom! Unsolder signal wire, which was a PITA because it went all the way through a thick double-sided board. Double-heatshrink the bare spot, put that amp back together, cable tie the signal wire out of harm's way, put the cover back on and clean the amp (can't send it home as dirty as it came in). Amp plays great, let it play for about an hour, keeps getting better as it heats up. Cool, all done!
Owner of shop asks, "How much for the repair you think?"
"What time is it? dang, took me three hours, but no way we can charge that, how about and hour and a half?"
"That may be pushing the limit for that kind of repair".
"Yeah, you're right, so $80 total".
Next day:
Owner of shop:
"Oh, there's a problem with the Aragon amp"
"Oh no, what?"
"The owner's brother brought in the wrong amp, he was supposed to bring the Accurus amp, which is blowing fuses, not the Aragon".
IF you're with me this far, hope you all have a nice evening!
BT
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- Re: The astronomical (relitvely) cost of repairs - BrassTeacher 17:42:39 04/21/07 (0)
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