M1.0t died with a pop

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snarffydoggy
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Re: M1.0t died with a pop

Post by snarffydoggy » Mon Nov 10, 2008 1:52 pm

Only Problem is we may have to wait for more parts. I hate when you can't run down to the store and buy what you need. Good Luck
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Re: M1.0t died with a pop

Post by brit01 » Mon Nov 10, 2008 2:11 pm

I hate when you can't run down to the store and buy what you need

I know that feeling all too well.

In my case I have to buy from overseas which just makes it even more fustrating.

I just want a local store on the corner like in the old days.
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Re: M1.0t died with a pop

Post by JBJR » Mon Nov 10, 2008 5:03 pm

Robert R wrote:I'd hoped we would do some voltage measurements before it ran very long. Something is suffering, obviously, in that hot running channel. Was that the channel that blew before?

I assume that when you ran it there were speakers attached.
How was the sound? Normal?

There are thermal shutdown devices, and one may have activated because of the overheating. Have you tried to run it again, after cooldown? Never leave it on long when it is heating up, no matter how good it sounds. At idle (no music) the heat sinks don't get warm so's you'd notice in 15 minutes, if it's running right.

If it's dead, even when cold, something has blown again, and were back to looking for shorted transistors, I suppose. Start with the ones that were blown before, obviously.

Then we have to figure out why they blow. First step in that is to check that the operating voltages are normal, and set the bias current adjustments. You have the right meter to do that, and I can guide you through it - it's not difficult.
Mis-bias can make for hot running, or there may be other stuff going on.

Robert R
Robert, Yes, that is the channel that went before. Good news, I turned it back on and it came on!! Must have shut down because of the heat. But, it did make the pop sound when it shut down.

I did have speakers hooked up to it and the little I heard it did sound normal, but, it was sitting mostly at idle for the 15 minutes. I do notice that it does turn on different than my other 1.0. When I turn that one on the LEDs light from the top and drop down to the bottom ones. On this one when I turn it on only the bottom LEDs light up. Thanks again Robert for the help with this!

John
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Re: M1.0t died with a pop

Post by Robert R » Mon Nov 10, 2008 8:08 pm

I thought the heat was shutting it down; now to figure out why is it getting hot.
We need to do some voltage checks. Find SRV 301, a little adjusting potentiometer near the center-rear of the main board, sort of between the two big filter caps. Unplug everything: the amp, the preamp inputs, and the speakers. Ground the black voltmeter lead, and set the meter (unless it is auto-ranging) to measure in the range of 100 volts, DC. Now find test points TP 5 and TP 6. They are on the right side, about an inch and a half in toward center from the little copper coil (L102). They consist of just jumpers, like so many others you see there, everywhere, except these have a little semi-loop on top for connecting test probes. Hook to TP 5 and plug the amp in and run it, reading the meter.
At TP 5 you should read 100 volts DC, and at TP 6, minus 100v DC. Adjust SRV 301 to get as close as possible to these values; don't fuss to excess, though. It should be pretty close to start with, but it probably hasn't been checked in 20 years. Be aware that the moving metal part that your screwdriver touches, besides being flimsy, is electrically hot; little danger to you, but best to not let the screwdriver blade touch anything, like the back of the chassis. You should have leeway on either side of specified value when adjusting these pots.
If these voltages are somehow in doubt, stop and post your findings. Even if the voltages are perfect, pull the plug. The next test wants a cold start.

Remember, for a few minutes there is some considerable remnant of that 100 volts still charged up in those big caps, so don't get grabby in there.


To adjust the idle currant (bias): If you look at the two heat sinks, you'll notice that each has a little tiny board on it, near the back, with a three-wire lead running to the main board. Those are the overheat sensors that monitor the heat sink.
At the other (board) end of those wires there are little potentiometers, one for each channel, named SVR 101 & SVR 102 that set the bias currents.

First connect your voltmeter to two test points for the right channel; they are called TP2 and TP4. These are vertical pins that stick up over near Q 130. Put your + lead on tp2 and the minus on tp4. (Yes, this is one time we DON''T ground one lead of the meter). Be careful to not let the probes short to anything else. You are looking to measure just 0.5 mV here (That's one two-thousandths of a volt). Not much, so if your meter is not auto-ranging, you'll probably want the most sensitive scale, but it's best practice to start out on a lot higher scale, for the safety of the meter, then work down. You will be adjusting SVR102.
When all is ready, turn the amp on and read the voltage, roughly. It should be very low. Then dial down to where you can read the voltage accurately. Try adjusting the control a little - it might be a bit rough and jumpy with dirt/oxides, so work it back and forth a few times, that might make it steadier. Little growls from the big transformer are normal when doing this. You should be able to adjust it to either side of 0.5mV. If not, we have other problems still, for sure; shut her down and post results. If you can set her to 0.5 mV, do so at about 2 minutes after turn-on. Now let her run long enough to see if the right heat sink is still heating up excessively. After a few minutes it should be very much like the other channel in temperature. If it is, leave her on for a while longer, to be sure there is still no heat buildup. If none, smile. If the right still heats up, well... we've got another job to do.

Even if all goes well, you still have to cool her down and check the bias setting on the other side, left channel. Same procedure as before. To set up your meter for the other side: TP1 for +; TP3for -. You will be adjusting SVR 101 this time.
First take a break and let the thing cool off for 10 minutes, to pretty dead cold. Then plug in and read the left channel bias value and adjust that to the same, 0.5 mV.
It should be somewhere near correct value to start with.

Now a longer test is called for - don't put the cover back on yet; it's considered bad luck by some, tempting Providence by others. To me, it just makes no sense, until we're sure that everything inside is finished. Run it, and keep an eye on the temperatures of the two channels. Unless you're playing some really unbalanced program material, they should be close in temperature.

Robert R
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Re: M1.0t died with a pop

Post by JBJR » Tue Nov 11, 2008 9:13 am

Ok Robert, off to do some testing and will get back to you with results.

Don't worry, I know all to well about voltages in equipment, the projectors I work on run at 35,000 volts, and you have to stick your hand in there to do some of the setup adjustments [-o< :shock: !

John
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Re: M1.0t died with a pop

Post by JBJR » Tue Nov 11, 2008 10:17 am

Wouldn't you know it, when you need it I can't find my small screw driver, off to rat shack to pick one up!

However, did take some quick readings, 102.253v on SRV 301 and the same neg on TP6. The bias on TP2 and TP4 was at .196. While in there though felt Q128, and Q130 and they were VERY, VERY HOT for that short time! All others felt cool to slightly warm. Do we still have a problem here?

John
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Re: M1.0t died with a pop

Post by Robert R » Tue Nov 11, 2008 12:50 pm

Zappo! 35KV - sounds like my TV repair days. 25 K was normal, but if the regulation was shot, some could rise to 40K, and it would sound like a war inside, all the arcing.

Let's see whether you can get the bias down to normal, then worry about the heating up. At some point we might reach the limits of my poor expertize, and have to call in the guy with the most M-1.0 experience, namely RichP74. Especially since I just got back from my chiropractor and he fixed my terrible lower back that I strained a week ago. My orders are to either lie down or walk, mostly the former, for several days, and I can't work on the computer in bed. No internet in there, and besides I type badly enough sitting, much worse lying.

RR

PS -
A non-metallic tool is best, if they carry such a thing. Used to have them for adjusting powdered iron coil tuning slugs.
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Re: M1.0t died with a pop

Post by RichP714 » Tue Nov 11, 2008 1:11 pm

Robert R wrote:.....he fixed my terrible lower back that I strained a week ago. My orders are to either lie down or walk, mostly the former, for several days, and I can't work on the computer in bed.
Ouch. I pulled my lower back out waterskiing a few years back (with a 'pop') and did the 'old man' walk for about 6 months. Get well guy!

I'm off to a Dr. appt right now, but will get back with bias setting instructions if you don't have them already.

Quick one before I go off. the adjustments are near the end of the three wire ribbon cables on each side of the amp, and the test points are near the center, near the heatsinks of each side. 0.5 millivolts dude, I'm assuming your earlier readings of 0.196 were volts (that's 196 millivolts, way too high)

Also, that 102VDC top rail should be set to 100VDC first with the adjustment in the middle of the amp, behind the transformer and near the back.

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Re: M1.0t died with a pop

Post by Robert R » Tue Nov 11, 2008 2:12 pm

Rich,
Thanks for sympathy and helping out. JBJR already has the voltage and bias setting instructions, but as you say, the one he measured (his very hot-running right channel) is way off. He had to go tool shopping before he can try adjusting - that's where we left off. If he can't bring it around to spec, I don't know how to procede with him, anyhow, except to check the individual rail voltages and a few other places.

If you refer back just a couple of posts you can see where we're at, to this point.

I waited for my back to get better on it's own, too long. My super-genius applied-kinesiologist reset everything in about five minutes, for all of 35 bucks. Should have gone right away; instead I was sitting in a chair, typing, for 5-6 painful days. I'd managed to pull two muscles, and then fluid builds up in the new spaces near the spine. I'm to walk a mile several times a day, and lie down the rest of the time, using ice packs, 10 min on, 10 min off until the inflammation and fluid are reduced. A couple of days, perhaps. It's sort of a full time job, so I must minimize computer time; I'm writing on a laptop in bed, in Word , then will drop into forum and send, all standing up. No chairs allowed. Luckily there are the Silver Mk IVs in the bedroom, so things could be a lot worse.

Robert R
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Re: M1.0t died with a pop

Post by TNRabbit » Tue Nov 11, 2008 3:21 pm

Get well soon, Robert.
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Re: M1.0t died with a pop

Post by JBJR » Tue Nov 11, 2008 4:09 pm

Hi guys, back from rat shack with new screw drivers. Robert, exactly those voltages are inside a Marquee crt projector! use your right hand and keep your left in your pocket!

Rich, those readings were from the standard vDC setting. Ok, got the top rail set to 100v. The bias is another story, set the meter to millivolts and the reading I got was 88.34. Turned it all the way down and it stays at 1.99 to 2.22, can't get it to go any lower adjustment is all the way to the stop. But, the heat problem is gone now. The left channel is currently reading 6.82 without adjustment.

John
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Re: M1.0t died with a pop

Post by JBJR » Tue Nov 11, 2008 4:38 pm

Went back to make more adjustments. The left channel is now at .5mV and I left it sit for a little while to make sure it would stay. The right channel did adjust down to .5mV this time, but, slowly started to rise and continued up to around 6mV. I kept adjusting it down, but to no avail it continued to rise and the adjustment was all the way to its lowest stop.


John
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Re: M1.0t died with a pop

Post by RichP714 » Tue Nov 11, 2008 5:22 pm

JBJR wrote:Went back to make more adjustments. The left channel is now at .5mV and I left it sit for a little while to make sure it would stay. The right channel did adjust down to .5mV this time, but, slowly started to rise and continued up to around 6mV. I kept adjusting it down, but to no avail it continued to rise and the adjustment was all the way to its lowest stop.


John
SOunds like something's askew somewhere (both trim posts should be set at about the same position, just a little bit off center, pointing toward the back is generally ballpark), but lets try this first.

First off, with both pots at dead center the idle current should be relatively nothing, so I'm thinking something's up in the bias circuit. Let's find out.

This is another (and IMO better) way to set bias. First warm her up (crank some music for about 20 minutes). Then cut the music and set both channels for 2.5 millivolts instead of 0.5.

What this does:

The idle current adjust is a dead cold adjustment usually......setting it for 0.5 millivolts does two things:
1- there's a tendency for you to accidently set it too high (if you look at this on a scope there's nothing, nothing, THEN an slight rise as you tweak). If you do it by scope that's okay, but via multimeter you're going by the meter's accuracy and the tweak pots sensitivity, VERY hard to get it right.

If you set it at 2.5 millivolts while hot and playing nothing it's easier to adjust and the likelihood of you setting it too high (where it'll creep higher and higher into thermal runaway) is dimished.

So,
try the 2.5 millivolt setting and tell us if they both are set at about the same location on the dial; we'll go from there.

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Re: M1.0t died with a pop

Post by JBJR » Tue Nov 11, 2008 5:34 pm

Ok, I'll give this a try. But, first have to run the girlfriend out to look at lighting for the kitchen and bathroom. Hope this won't take to long, but, you know how that will go #-o [-o< :lol: !!!

John
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Re: M1.0t died with a pop

Post by brit01 » Tue Nov 11, 2008 5:50 pm

Yep. Don't forget about your other half. I had some compensating to do after my 26 page thread with Rich 8-[ 8-[

Looks like you've got yourself another bias problem to fix Rich.

I'll take a back seat this time and watch until my parts come in from your side :D :D :D :D

Good luck with this one.
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