How to Troubleshoot Amplifiers Stuck in Protection

[@luispendragon6551]

I was always shy when looking at a block diagram...but man I can see so clear when you speak of It. Thank you Ray of light. Peace man.

[@raygianelli3612]

It's a skill learned over time. I know it seemed like forever before it started to fall into place. Just keep at it, the understanding will come.

[@DaXande135]

My words! I also understand more and more of these block diagrams the more I see someone explaining it bit by bit.

[@robfors]

Ray, another excellent video. Very detailed and conscise. Thank you for your hard work!

[@raygianelli3612]

Thanks Rob! It's not work if it's something you enjoy.

[@robertcollins224]

​@raygianelli3612 I got screwed today. I bought two "open box" Radio Shack MPA-250B PA amplifiers. When I powered them up.. protection mode.. I'd like some guidance. There are NO SCHEMATICS to be found anywhere. This sucks! Merry Christmas to me!! Any help would be AWESOME!

[@cwradio4571]

Absolutely the best video on this subject. I will be recommending this to people when they ask about subject. I could not have done it better.

[@raygianelli3612]

Thanks CW, you've made my day!

[@Douglas_Blake_579]

Well done ... and very easily understood. This issue ... DC Offset and shorted outputs... is a compelling reason to use a "Dim Bulb" current limiter on your test bench. (Basically a 60 watt light bulb in series with the AC power cord) I never fire up an unknown amplifier the first time without one. I actually learned this lesson the hard way ... I had a GSC on my bench, locked into protection, no speaker output... but one of the outputs was shorted across and in a fight with the offset regulator. I watched that amp go right up in flames... and as we know, when you let the magic smoke out, this stuff tends to stop working. A dim bulb tester would have warned me and kept the current to a safe value.

[@raygianelli3612]

Douglas, it seems like I have to learn ALL my lessons the hard way. Oh well, those lessons do stick!

[@Douglas_Blake_579]

@@raygianelli3612 They sure do.

[@jameswaddington7913]

Hope I learned something? You turned on the light! I have been fumbling around with a NAD2200 and you have enlightened me. Now I have a much better understanding. I thank you.

[@raygianelli3612]

James, you made my day! That's just what I'm trying to get across. I'm firmly in the "teach a man to fish" camp. My goal is to share the knowledge taught to me and the experience I've gained in order to give back to the community.

[@markcaruana7233]

Use of multiple examples along with detailed clarification between designer drawing notations is golden. Thanks for and keep up this method of instruction.

[@raygianelli3612]

Thanks Mark, I will keep it up. I appreciate the feedback!

[@ziggfreud9820]

That was awesome. I really appreciate videos such as these. I can understand them and learn a great deal.

[@raygianelli3612]

Appreciate your comments, Zigg. When I see someone say they understand something I've posted I feel that I've accomplished what I set out to do.

[@TJET737]

Most excellent video. One of the best I've seen out there that is easy to understand. thank you for your time in putting this out there.

[@raygianelli3612]

Thanks TJET. That's what I'm shooting for, so it's nice to hear that it was understood!

[@robertcox5228]

Hi Ray excellent video. Went through the steps you mentioned. Relay would not pull in. Scratched head. Found relay coil open. Duh.

[@raygianelli3612]

Good work, Robert! Not a common problem, and therefore can be one of the last things you'd check.

[@texdentist]

Great video! Lots of neat tricks and tips. Thanks for making it and keep 'em coming. 👍

[@raygianelli3612]

Thanks Steven! Doing these videos really forces me to focus and think about this stuff in ways that are, frankly, beneficial to me. I hope it is to others as well.

[@g.fortin3228]

Wow another GREAT one ! Love the story about the voice coil too. I'm inspired to get to testing an amp pretty soon. Practicing on a random old board for desolder / resolder skills first. Thanks again for the insight. Really great stuff!

[@raygianelli3612]

Excellent idea to practice on old boards first. I can assure you my first patients did not fare well!

[@marnav9205]

I enjoy your videos very much Ray. Please keep them coming, thanks.

[@raygianelli3612]

Thanks you, Mar. I'm sure there are many more to come!

[@BillEyles]

Great content Ray as always this will help me as I'm fighting a Fisher 2010 that's stuck in protection

[@raygianelli3612]

Bill, as I said in the video there's only two scenarios; either there's excessive DC on one of the output stages, or the protection circuit itself has failed. Let me know how you make out!

[@TheSoundtec]

Great Video Ray ! I just subscribed and I was very impressed. Im a Tech of 40 years and I came across a Teac A-X55 and Im tearing my hair out. Supply is ok, Protection Circuit is ok, Emitter resistors have mv only. Relay is good and Still the relay will not close on startup. Wish we were neighbours.. Cheers

[@raygianelli3612]

Well come on down here to South Florida. The weather's great this time of year. Summer is another story, though! Shoot me an email. My contact information is available if you click the line below my subscriber and video count. Always happy to help out a fellow tech!

[@smbanandanand4566]

Very useful video and very well explained, thanks (from India) Ray !

[@raygianelli3612]

Thanks for the kind words! Life is getting in the way of working on this stuff. I hope to get back to it soon.

[@briang.7206]

Thx another excellent tutorial.

[@Jerry-vz4ix]

Thank you, this was helpful, I am looking at a ADS R1 (Same as a Braun R1). last two days, that protection circuit has been driving me nuts. Think I just narrowed down what the problem is. (again, thank you!)

[@raygianelli3612]

Thanks Jerry. It's always nice to hear that these videos are helping someone!

[@sirsuse]

Thank you Ray.

[@raygianelli3612]

👍

[@Jerry-vz4ix]

side note, If you replace those STK-50s do you have do any adjustments, I looked that voltage on the base of the protection circuit transistors, they're sitting at (effectively) zero V. So I don't expect any problems once I replace that delay capacitor (it looks suspect). But still, I don't know for sure what you're suppose to do once you replace those STK's.

[@raygianelli3612]

While I'm not familiar with that particular unit, most only have adjustments for the output stages. That should hold for STK or discrete designs.

[@Jerry-vz4ix]

@@raygianelli3612 IDK there's a lot of discussion around those STK series Modules. But the factory that made them was destroyed in an earthquake, Any replacement you get is likely a chineese knock off (and from all reports, not as clean as the orginals. There's a kit, it's heatsink and circuit board (with discrete components) you can mount and it's suppose to work better than the knockoffs. Idk that I will do that See, the unit had multiple problems, power related as well as the protection circuit. I'm hoping I kept the originals that came out of it. (I probably did) And will put them back in once I get it up and running. as far as the circuit protection I looked right at the voltage, and said.. that's not right. I did some math and came up with 7 vs the 2V I was seeing. But It never dawned on me that this was a delay circuit. Once you pointed that out, then it all made sense. Plus, the manual (as scant as it is), is written in German. Not helpful ... lol But again, thank you.

[@raygianelli3612]

@@Jerry-vz4ix Parts availability is going to be an issue for many items going forward. I need to work on my SMD soldering skills... which are pretty much nonexistent at the moment.

[@Jerry-vz4ix]

@@raygianelli3612 yep, were both of that age when eyesight isn't near what it should be. One thing I will tell you indispensable, is one of those video cameras/ microscope. Ya'd think it would be hard soldering while looking at a video monitor, but it's not. Take a little getting use to. But once you do, you'll never go back to the goggles. plus, they aren't as expenive as you'd think I picked one up for.. wanna say it was less than 150 or so. Make sure it's at least 1080p at 60hz The other thing that makes life easier (but is more costly), is hot air.. not a gun, but it is. Really small nozzle, I haven't picked one up yet. So far, just working without it. I did pull out that cap and check it. ESR was 11 ohms, the capacitance was less than half of the stated value. this thing was build back when a lot of bad caps were being sold in the supply chain. They were knock offs coming out of china, half of the problems i've been running into are those caps going bad. Eh, what can ya do. ESR meter and check em all. I guess. Course replacing that cap just revealed other problems. This amp is a basket case. Not worth money in time I have into it. But, Nothing else is on the workbench. It goes on the bench when I have slack time, or off when I have something else to do. Right now, redoing some traces that burned when it failed. So that will take a little time. If it wasn't so cool looking, I'd pull the transformer and throw it away.

[@raygianelli3612]

@@Jerry-vz4ix Yeah, I'm looking into video microscopes, among other things. Hot air station too.

[@roroseppel2077]

Great video, thanks a lot !

[@raygianelli3612]

Thanks Roro. I've had a lot of questions about amps in protection, so I thought this video might help.

[@RectifiedMetals]

Boy do I have one for you. This one, a big AVR, it will not power up unless I disconnect the amplifier modules. I have tested every single transistor, on all 7 channels. I can imagine your look if you saw it, shaking your head, “Not Another Defective.” …. Or the brand has some initials here… 🎃 Great video!

[@raygianelli3612]

Buddy, AVR's are a bear to work on! Even a simple 2 channel receiver with IR remote capability is magnitudes more complex than one without. Add multi channel and surround decoding circuitry and you're in no man's land. I tend not to work on them simply due to the fact that they lose value faster than a new car driven off the lot!

[@RectifiedMetals]

@@raygianelli3612 💩 you’re not kidding about that. I can’t stand them, but every time I work on them it brings my customer closer back to 2 channel. Reversing consumer thinking from the late 90’s marketing damage is slow. Eventually they come around and reinvest into 2 channel once they realize 90% of their tv stuff comes only from one speaker.

[@masoudmontazery907]

Good luck sir

[@Bluelagoonstudios]

You have to see to an amp, like it's modular, can't go wrong, measuring is knowledge. That's how I see it, I'm building an amp myself these days, and they are all modules. So if something's go wrong, you can see right away what is wrong. I hope this build is ready about a month.

[@arnoldrimmer8008]

My SX-850 doesn't have a fly back diode but it is a popular mod for this unit. I was working on system that uses a braking motor. The brake was controlled by a relay. We were concerned the kick back was affecting the PLC. So we installed a fly back diode and it delayed the action of the brake. So the axis would overtravel (not stop in time) and hit the limit switch. Would adding a flyback diode to the speaker protection circuit reduce the effectiveness of the protection circuit?

[@raygianelli3612]

Very interesting, Arnold. The SX-950 doesn't have one either, but by the SX-1050 one was installed. The diode won't adversely affect the protection system, since it is reverse biased until the field around the relay coil collapses, and the diode becomes forward biased, which prevents the buildup of harmful voltage. The flyback diode should not affect the brake in the PLC system, since the relay contacts are what interfaces with the brake. Make sure the diode used has a high reverse breakdown voltage.

[@Trucam2020]

As usual, excellent video. Thanks Ray.

[@raygianelli3612]

Appreciate the kind words, Uri!

[@heriberto3313]

What to do if no speaker is connected and still go protected mode sooner you turn on the amplifier

[@raygianelli3612]

Same procedure. Trouble is either excessive DC at output stage, usually caused by a blown channel, or a trouble with the protection circuit itself. Speaker connection doesn't affect it, because the protection circuit is there to protect your speakers.

[@mr.mrs.witowski29]

Damn, that must've been a searing lead solo you did!

[@raygianelli3612]

I wish it was. I got decent but never what I considered good.

[@heriberto3313]

And thanks

[@garydirkse9900]

If the light is blinking, sounds like a bistable. One blink should be a monostable.

[@internet123ism2]

There's a whole language here I'm not familiar with. I need something more elementary. e.g. "forward bias leaning"...I have no idea.

[@raygianelli3612]

I don't know what "forward bias leaning" is either, but forward bias is the term used to denote when a transistor begins conducting.