Where Did The Current Flow Part 2 : Basic 400 BiAmp Active Speaker Repair
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- Опубликовано: 29 сен 2024
- A Customer brought me a Basic 400 Bi-Amp from an Active Speaker. It is faulty but I need to find out which component is causing the problem. Something is drawing more current than it should. How can we find out what it is?
Follow this repair:
Part 1
• How To Diagnose IC Fau...
Part 2
• Is The IC Faulty Or Is...
Part 3
• How To Measure Current...
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Thank you
Richard
I only ever had a expoxy'd down chip once. So my sample size is limited. But my idea was to thread a string of dental floss under the legs from the side. Then I pulled it back and forth and worked it through the resin glue like a string saw. It was a bit fiddly to get in but after that, it went really well. No damage to chip or board. If that hadn't worked, I would've tried acetone. But I read that it might also dissolve solder mask and silkscreen, so I tried the dental floss first. And it worked.
This was my idea also, because I have used dental floss in other situations to cut glue without damaging the surface beneath. Maybe it would be easier too cut the legs off flush with the body off the component, and unsolder/remove them before cutting the glue with the floss. If the glue is too hard for the floss, you could try a guitar string also... But easier to damage the board with that. Dental floss can cut surprisingly well 😅
Oh oh , Richard.
Your desolder temperatur and time was to high, long.
Delaminated areas and bubbles on the pcb😭.
Didn't have you leaded solder?.
Because, good repair video👍👍👍
I added leaded solder to the pins then used hot air, you do know that I know how to desolder stuff without frying the PCB. The problem with these sort of PCBs is that every component (even the smd resistors and caps) is glued to the board with what looks like 2-part epoxy resin of a type which is very hard and heat resistant. So using hot air the PCB tends to give up before the glue does. It takes maybe a couple of minutes direct heat to get the glue to give it up and when it does the chip tends to ping off the board like a tiddlywink. For sure this sort of repair needs a different technique to unsolder components which is one reason I wanted to highlight this here to hear other ideas. Have you yourself come across these type of boards before? Maybe heating until the solder melts then getting something thin and sharp down under the chip may work but I haven't tried it. Sometimes the components are glued down with a reddish coloured dot of something and they are not so bad to unsolder but this type of glue 00:22:58 is a real pain in the butt.
Hi Richard 🤗.
I know your problem😨. The first is to use leaded solder. The second is to work with a larger hot air nozzle. The third is not to use SMD tweezers but rather stronger ones (possibly needle nose pliers). These glued SMD components are really torture. You do a great job👍👍👍👍, but your long, thin blank measuring tips scare me.😳😳😳🤣🤣🤣
@@LearnElectronicsRepair,, ohh i forgott. To reduce the delaminating and bubble's you must preheating the pcb. E.g. 1-2. Hours at 50-80C° in the Ofen. The humidity in the pcb is the problem.
@@Lightrunner. Thanks for the suggestions, I can try using the preheate and hot air together. Melting the solder is not the problem here, it's getting the component off the board.
@@LearnElectronicsRepair no no , not together. First the humidity must out of the pcb(preheater 1-2 hours at 50-80C°). After that a cool down is recomended. Then you can work normaly with your hot air cautios👍👍👍🤗🤗🤗
On that ST chip that didn't have the dot marking pin 1 - pin 1 is actually marked with a slope on one side of the chip. If you look from the side you will see that the plastic isn't symmetrical
Yep. Some IC's are marked with a 45 degree chamfer down one side. It's shown on the data sheet for that chip.
Wow... To me I learned a lot from this video, The discussion as you probed around was great,... And the one tool which I'm glad to see you get out,... that was the scope with the signal generator... And I wanted for many years to do some circuit tracing using a signal generator. And you demonstrated some aspects of using that tool to trace down a problem, I hope in the future when opportunities arise we can inject a signal and see the capabilities and some reasons why that can help diagnose an issue without actually injecting voltage. I just want to gain some experience and knowledge in using such a technique versus probing around for a voltage. As far as the glue issue... Holy crap!... What a difficult problem, I think first off you won't know if the chip is glue down until you try to remove it... I'm wondering about things like drops of acetone or some kind of chemical that removes or affects glue, without harming the circuit board. One thing to get a feel for when removing these types of ICs is when it just doesn't come off the board like it should... A person should suspect it being glued in place. Maybe we can kick around a few ideas of why the manufacturer did that... It's at least something to share information about, I have some ideas why they do that... But to make the part during the removal process for replacement potentially damage the board kind of pushes me in the direction of the old saying... No serviceable parts inside 🙂 again when appropriate toss some ideas out there for discussion. I once worked for a company in the secret ingredients to make the circuit work the way it did... We would erase the identification of the part, it was a way of protecting the circuit design. again great video, showed the decision-making process when deciding to remove components and weighing the good in the bad. Can't wait to see what develops when we take the next steps.
Hi Rich, try a tiny drop of acetone, works for me most of the time. It needs to sit for a while. Also, paint stripper or thinners definitely removes conformal coating.
Det also suggested Acetone I will have to get some
@@LearnElectronicsRepairwife’s nail polish remover 😊
Agree. I use acetone. Let it sit and soften the glue. Be careful though, acetone doesn't take any prisoners so only get it on the parts you are trying to remove.
I enjoy watching your videos and I am learning so much practical stuff. I would love to have a brilliant suggestion to help with the glued components but without knowing the type of glue I can offer nowt but “Thanks for sharing so much of your experience and knowledge”
It's very hard, like 2 part epoxy resin.
@30:38 Is your meter reading 0.639 MegOhms? That's a 100k resistor you are checking there, not 1 Meg. So it looks like it's reading high, not low.
For the 2 legged components, you might try the twist off approach, which is often recommended (e.g. on Bose wave radio repairs where all the SMD caps need to be replaced). Amazingly, that way the pcb seems to get less damage than from the heat during desoldering
Hi Richard, I have previously used solder wick on one side to slight lift the legs, and then slipped a sharp blade to slice the glue. Thinners or even petrol is also an option if you let it soak for a while. If you have a thin blade, prelifting may not be necessary, depending on the ICs stand-off from the board ?
Maybe the tester doesn't work on 393s because they have an open drain output, so they need a pull up resistor to function properly
I suspect that, from a commercial sense, this repair is already beyond the point as to be viable in terms of cost to a cusomer and is continuing as it's interesting from a learning and content view?
How do you make that call for customers on less interesting repairs?
Yes and no. So this customer offered me a lot of work to come after I fixed the HK Lucas Subwoofer that someone else had looked at and couldn't fix (the one with the open circuit 33K resistor). So I'm trying to impress him a bit. Also I do use these jobs to make educational videos on various aspects of repair work so I sometimes go a more roundabout way to the destination than I might.
To me using "Lacquer Thinner" and/or "Acetone" and then wait 10 minutes and repeat, then wait another 10 minutes and then and only then !!! attempt to un-solder and remove the IC works every time. But I'm yet to also try the paint stripper method but fear that in the process the whole green protective layer will go too. Perhaps, the "Acetone" method is best after all.
Freeze spray to see if opp amps come back to life? I hate that glue under smd. Probably soak in alcohol b4 removal. Would like to know. If you are expecting the glue then get a pick under the chip and pry once you are sure the solder is ready.
Im following this amp repair like a series of Eastenders, Will it survive?? who knows but its very entertaining , Great work explaining as you go through it.
What IS THE POINT from the manufacturer's perspective to glue smd components to the PCB? What am I missing here? I don't get it 🤔
Ruggedness against mechanical forces when the equipment is being thrown around (as stage equipment often is)
@@Chief_Engineer SMD soldered components falling off?!? You'd have to throw the whole thing out of a 10 story building before they moved 🤣🤣🤣
@@chillidogkev don‘t forget they are only held in place by the solder pads.
I am wondering if it is a type of "conformal coating" thing they used under components, and maybe a bit of acetone will remove / loosen? or even 99% alchohol?
I've been faced with damage situations on a recent clock counter board repair for a PC case. it's particularly a defective LED component that needs to be swapped with a new unit.
Yeah, I feel your pain! sometimes jobs start going from bad to worse....cheers.
I enjoy the information you share with us , thank you very much. God bless you 🙏🏻.
MG Chemicals 8310A may work
Sir you are kinda god to someone like that just started learning electronics
As a newbie with micro soldering I would have preferred that you had started with signal tracing to find the issue in-situ to avoid any variables that might be caused with mass chip removal. In retrospect you may have wish you did :).
I haven't experienced chips being glued down so rigidly so I would have tried lifting the pins then trying different solvents. In fact, since you have dead chips with glue stuck on them perhaps they could be used to determine a working solvent provided the heat didn't alter the glue (thinking baked on enamel). IP, acetone, and naptha being my first candidates. I imagine some soaking would be needed and I would affix some tissue or cotton around the chip to hold the solvent if part is still on the pcb.
After the third 105 resistor I was suspecting a meter issue, too, and can't imagine how so many were killed. Are resistors in that value range less susceptible to damage due to low dissipation or more so due to a 'thinner' internal path?
Still a great video (as with most) as you've been teaching me so much. Cheers!
The 1M resistor issue is a strange one, I've not come across that before. They are all glued down too! The method of reverse engineering and then signal tracing (I have no schematics for this) or remove the six IC and test/eliminate them first was one of those decisions you face while fault finding. I think I made a good case in the video for the direction I decided to take. Doesn't mean it was the best one in retrospect though 😉
Have you tried using flux & hot air repeatedly & wiping with a micro fibre cloth to remove the coating, then adding some chipquik
This isn't a coating on top of the component, it's very hard glue underneath it
Odd that every component is glued! I pesume since this is a powerful speaker it produces a lot of vibration that could crack solder joints and the glue prevents this.
The SMD components are glued on due to the production process of the board. It's a mixed THT and SMD board and has probably been wave soldered. So when moving the underside of the PCB through the molten solder bath all the SMD components on the underside need to be glued on to not fall off.
@softminer OK, thanks for the info.
,,, snip the 8 legs of those surface mount op amps to ensure you don't lose pads - remove glued body with knife blade. So you do just replace to avoid damage.
No, snipping the 8 legs of an IC is definitely NOT! a proper solution. What is you just want to test the IC and then put it back if tests ok simply because you don't have another one to replace with ? Destructive displacement of any component ever anywhere anytime is never a good idea. Acetone does wonders in this case providing you are patient enough for a few minutes. Good luck.
@@ovi_4 might not be the proper solution - I think it is what you might wish you had done in hindsight, specially if you already had these new low cost parts to use.
For glued on components using hot air, once the solder has melted I twist them off to avoid burning the board. I usually do this under the microscope so I can easily see when all joints have melted to avoid tearing tracks.
Edit: The bigger the component, the more difficult this becomes from the extra glue.
I also use low melt on the pins to keep them freely moving as I twist the component to break the adhesive
That sounds like it could work. Ican clearly see the solder has melted (I added some unleaded before using hot air) but the component just does not want to come off the board
I love your videos
Enjoyed lots 😁
So master what happens if two opossit currents meets in a conductor, they cancel out and produce heat,I am curious
I'm not totally sure what you mean there because I can't understand how you can have opposite currents in a conductor. Current flows between two points depending on the potential difference and that can only be in one direction at any given time
@@LearnElectronicsRepair master excuse my naivenes, but I thought i saw somewhere on RUclips a physics professor that said that kirkofs current law, and had different polarity currents on a node that was cancelling each other and it was zero at the end , maybe i didn't understand it well 😞