The community repair thread

Danny1969

So here's an easy little job this morning. A little Mackie mixer which customer says only works on one output channel. For fault finding on desks I find it easier to connect an iPod up playing some music and then I start. 



So you can see the signal from both channels is going to the main master bus but there's no output on the right side from the unbalanced jack socket which is what the customer uses. Well I know the fault is in the master bus side of things and experience tells me it's rarely component failure on line level mixers. These things  are basically just a load of opamps which draw a very small current. Nothing gets hot so any failure is almost certainly a bad joint or a bad socket. 

What you generally find though is a bad joint on a mixer often acts like a semiconductor ... there's no signal getting through somewhere until the voltage  exceeds a level and then boom, it's there. This is why I never use continuity testers to test audio leads. They can test fine with a steady DC test voltage but fail with a very low microphone AC voltage. So I wind up the fader level from the iPod and the broken channel cuts in and both sides work. So I know it's bad joint or bad socket. 

So here it is apart, PSU moved out of the way so I can get to and resolder the jack socket. 



Have to say it's very well built and the solder joints look good but I reflow them anyway and then clean the socket with switch cleaner. I find covering a jack plug with cleaner and inserting several times quite effective. 






And it's back up and running and no problems even with very very low levels of signal going into the desk. I made sure all the insert points were cleaned to as if these break contact you lose audio at the channel stage. 


  

Chris.B

It's great to hear of another successful repair, much better than the Mackie ending up in the bin. 

Danny1969

So this was todays big win on my repair bench. Macbook Pro's are very popular with musicians and this is probably the best Macbook Pro ever made. The 15" Retina A1398. Certainly this model is my favorite, it's powerful with a quad i7, the screen is superb and it's got all the ports, unlike the modern crap Touchbar models. These 15" Retina's do suffer from one fault though and this one has been written off by the customer because it needs a replacement motherboard.  I'm 90% certain I know what the fault is though, not because I'm clever but because I've researched it and matched the symptoms to a known flaw with this model. 



So the fault manifests with a loss of video. You might actually think the machine isn't running but there's an easy way to tell. Press the caps lock and if you can turn it on and off and see the light then the machine has posted but you can't see it because there's no LVDS video. So bottom off 



First job is always unplug the battery. Now you make a note of where every screw goes and what kind it is. All the screws are torx, all are different in length and profile so you need to make sure you know where you took each screw from. There's 3 different type screws for each fan for example. Then carefully unplug all the connectors for the KB, palm rest, speakers, fans etc. Then you can take the board out. 



Now the fault is with an IC that controls power to the GPU, a QFN package chip which is a 62882 regulator. It's on the other side of the board which is why I've taken it out. Here it is 



I tried to take a good photo to show what the problem is but my phone camera isn't good enough. Basically the package has 40 pins and the solder joints crack after a while meaning the GPU loses power hence the blank screen. Now this is small QFN chip which is a lot harder to solder than your average opamp but still perfectly do-able if you use a lot of flux and a pointy conical tip. 
So I resoldered it with leaded solder and did a neat job. You have to be 100 % certain you haven't bridged any pins otherwise you will quite likely destroy the GPU. I've cropped this pic and tried to get the chip in focus but needed more light really. However you can see the joints are now looking good. 



So put the board back in and was very pleased to see it now has video 



The fans were running full pelt when it started booting which concerned me but then I remembered I hadn't plugged the palm rest in yet. There is a sensor in the palm rest that reads the battery temperature and if the SMC doesn't get the information it puts both fans into full RPM. Once I plugged the palm rest in all was well. 

So I hope this helps anybody who has a 15" Retina which exhibits this fault. It normally starts misbehaving a bit at first, especially if you move the laptop when hot but eventually gets to the stage this one was at, with no video at all. It's a much easier fault to fix than the GPU issue that affected earlier MBP's. 

Emp_Fab

You said the customer had written it off.....   does that mean you get a free Macbook ?  

Danny1969

Emp_Fab said:

You said the customer had written it off.....   does that mean you get a free Macbook ?  

I had to pay £100 for it mate as even a dead one of these is worth £300 or more. I'm actually typing this reply on it, very chuffed indeed as I wanted a dedicated MBP for running Mainstage at gigs. Great laptops 

Danny1969

So from a repairers point of view there's some bad news about the iPhone 12. It looks like common parts repairers like myself have changed for people to keep their phones running cost effectively, is coming to an end. The 3 main parts we tend to have to change are the LCD \ Digi, the battery and the camera. Now for the first time it seems there's firmware in all 3 parts that are paired to the motherboard and even changing the failed part for another genuine Apple part won't help unless we have a means of pairing the part to the motherboard … and that's going to a be specialist piece of Apple kit used in manufacturing and at the Apple store. It's unlikely to be available to buy. 

I'm not sure this is a deliberate ploy to prevent third party repair as things that can't be made to completely precise specifications do need pair coding. Even something like the piezo injectors on a diesel engine have to be coded to the fuel pump as they are all a little different. I'm thinking this is certainly the issue with the new camera but whatever the reason it's the beginning of the end to 10 years of happily repairing iPhones for me and a lot of other repairers. Love or hate Apple or Android phones from a pure repairers point of view iPhones were quick cheap and easy to repair. Sadly it looks like that's no longer the case. 



So if you get the new 12 look after it. Your only repair option could well be the Apple store. 

crunchman

Danny1969 said:

So from a repairers point of view there's some bad news about the iPhone 12. It looks like common parts repairers like myself have changed for people to keep their phones running cost effectively, is coming to an end. The 3 main parts we tend to have to change are the LCD \ Digi, the battery and the camera. Now for the first time it seems there's firmware in all 3 parts that are paired to the motherboard and even changing the failed part for another genuine Apple part won't help unless we have a means of pairing the part to the motherboard … and that's going to a be specialist piece of Apple kit used in manufacturing and at the Apple store. It's unlikely to be available to buy. 

I'm not sure this is a deliberate ploy to prevent third party repair as things that can't be made to completely precise specifications do need pair coding. Even something like the piezo injectors on a diesel engine have to be coded to the fuel pump as they are all a little different. I'm thinking this is certainly the issue with the new camera but whatever the reason it's the beginning of the end to 10 years of happily repairing iPhones for me and a lot of other repairers. Love or hate Apple or Android phones from a pure repairers point of view iPhones were quick cheap and easy to repair. Sadly it looks like that's no longer the case. 



So if you get the new 12 look after it. Your only repair option could well be the Apple store. 

Isn't this going to fall foul of legislation that is coming in to make things repairable?

https://www.theguardian.com/world/2020/mar/11/eu-brings-in-right-to-repair-rules-for-phones-and-tablets

There are campaigns on this in the US as well.  The US isn't as advanced as Europe on this, but it will come.

Danny1969

@crunchman …. no not really. There are many things which need specific code to be put into them … SMC chip on a laptop, firmware in a Line 6 product or a Helix, Kemper, anything with DSP in general. 

boogieman

Is that a new thing on the 12? If so I’m glad I bought an 11 recently. 

Danny1969

boogieman said:

Is that a new thing on the 12? If so I’m glad I bought an 11 recently. 

Yeah up to now you could generally change bits around without any issues other than the home button, which was code paired to the motherboard for fingerprint recognition. With the 12 it seems even changing the battery causes issues. 

On the positive side it gives me the excuse to stop doing phones but It's bad news for the end user who like to get 5 years of service out of their phone, as many iPhone users do. Hopefully Apple will operate a cost effective repair program but you can't help thinking it's good news for their share holders. Can't repair the iPhone cost effectively ?  then you buy a new one which is good for them, bad for the planet. 

Kittyfrisk

This news about the iPhone 12 repairability is really saddening. Not surprising, but not a positive move in my view.
I hear what you say about engine parts coding being a standard thing in the automotive industries, but at least there is the possibility for recoding/programming the parts to restore functionality.
Be interesting to hear the justification from Apple as to why they implemented it.

midiman1962

Danny1969 said:

So little favour for a friend today who brought a 9V adapter for his pedal and surprise it doesn't work as like 99% of these things it's centre pin is wired positive.
So here's a quick hack to change that around while keeping things neat. 

Cut the wire so both positives are long and both negatives are short. Cut a piece of heatshrink and to make things easier make 2 lumps of bluetack.



Slide the heatshrink over one end length of wire first, then position wires on bluetack  .... the fact you cut both positive wires long on each bit of cable now means the polarity will be swapped over when you join them. 

A neat joint is a piece of cake when sat on the bluetack 



Then slide your heatshrink over the joint and then you have a Boss type adapter 9V centre neg with no big joined lump in the cable and no chance of the wires shorting out because their joins are spaced apart. 

very useful - am just about to do this very thing - thanks for sharing

Emp_Fab

Hey @Danny1969 - re your Apple comments, I presume you're familiar with Louis Rossman's channel ?
https://www.youtube.com/user/rossmanngroup

Danny1969

Emp_Fab said:

Hey @Danny1969 - re your Apple comments, I presume you're familiar with Louis Rossman's channel ?
https://www.youtube.com/user/rossmanngroup

Yes mate, I've learnt a lot from him. There's a few things I've seen him struggle with which I would have sussed out much quicker but there's some things he's sussed out that i wouldn't even have thought of. People like myself also get to benefit from his investment in the schematics and board view software for all the Macbook Pro's. 
I've grown to like his typical blunt NY mannerisms too and the way he lets the camera into his whole life from running a repair shop to be ripped off from contractors to buying a house and building an E bike.  

My only criticism of Louis's channel, and some of the similar one's like Ipad rehab is they basically fix the same stuff constantly so it get's a bit boring. I purposely turn down too much of the same kind of work because I want some variety in my work.  Then again I don't have to pay 12K a month for a Manhattan shop lease

Danny1969

Well this is a fun job ... not, this is a TC bass amp, class D  in a let's see how small we can make it format. This has been on my shelf for a while as I said I would fix it in my spare time on the cheap for a friend. I've done a similar one to this before so it's a nightmare job I've been avoiding. Forgot to take a pic before I stripped it down so it's straight into the nudity. This is what the world of bass amplification is steadily moving over to. Underpowered shit little bass amps than go wrong and are a complete nightmare to fix. 

So this doesn't power up, completely dead because the switch mode power supply isn't starting. Looking at this nightmare we can see 3 sections ... the power supply, the audio control panel PCB and the actual class D amp. 



Generally when these designs fail they can fail in 2 ways ... fail open which I think this has or fail short which generally means multiple destruction of components. Generally I wouldn't advise anyone to have a go at these kind of designs. The mains input is directly rectified by the bridge rect so there's 320V DC sat on the primary side of the transformer. But it's a good example to show how modern amps are made. Basically the main input is rectified to DC and then a MOSFET transistor is used to switch the DC to the transformer on and off at a high frequency, typically 60Khz upwards. The high switching frequency means the transformer can be tiny in comparison to one that operates at 50Hz. The actual regulated DC output is achieved by modulating the transistor switching duty cycle which is modulated by the feedback sense circuit, called pulse width modulation. This means very good regulation with moderate heat and almost 100 % efficiency because the transistors are either fully on (saturated) or fully off. 

Everything is so crammed together and the boards have to come out before you can get to the other side of the PCB's. 



So the board in the middle, the power supply is where I'm pinning my hopes as the actual amp PCB looks virtually unfixable without detailed knowledge of what's going on and a schematic. Oh I forgot to mention the boards are populated both sides and the other side is mainly surface mount. 



So I've got 320V DC  on the cap and bridge rect but nothing is switching ... a bit of prodding and I find the switching transistor is open circuit. How this fails is generally open circuit,  which is good because it basically stops things there and then or it can fail short circuit which is bad ... I've had PA amps where it has failed short and taken out the PWM chip and a bunch of other stuff too. Now it's not generally a good idea to replace it and power up without wondering why it failed. 

So transistor out, note the clip that is used to keep it sprung against the heatsink. The transistor actually sits in a mica jacket to insulate it's TO-247 package from the heatsink. Now it's been ordered but in the mean time I need to work out just why it failed. Could be just duty cycle and the fact that it's not that well cooled or could be either winding short in the transformer. These can be quite complex to fault find as they bear no relation to a normal linear transformers ... the secondary can be the same side as the primary due to the way it's wound plus there's generally some aux windings to power things without the main sec side input. It's a £9 N channel MOSFET so I need to be sure I won't blow the new one up.  

I'll come back to this in a few days when I've had a chance to power it back up assuming the transformers good. 

 

Danny1969

Done a whole bunch of PC and laptop jobs this morning but this fault on an HP desktop is interesting as it's something you don't see very often so people don't suspect the culprit. The fault reported by the customer is the PC is running  very slow despite having an SSD boot drive and enough ram. The customer has run tests on the drive and on the hardware and everything comes up fine except the machine is dog slow. 
So I switch it on and Win 10 starts it's little circle loading thing and straight away I notice  it's turning very slowly and in packets ... as in a little packet of data then freezes then another little packet of data etc. until it's finally loaded. So it's a drive fault or SATA bus fault as at this point no drivers or software for the OS would be taking effect. Restarting in safe mode gives the same result. 
So if you ever get this scenario before you start taking out the drive to test it change the SATA cable. The SATA bus is basically 2 differential pairs running transmit and receive. If the differential side goes down it can still function and Windows won't report any errors BUT data transfer will be a fraction of the speed it should be. So one 89 pence cable later it's fixed 



  

Danny1969

So Beats wireless headphones ... apparently these are expensive. This pair only only has audio coming out the right side, left side is dead says customer. 



So these are Bluetooth re-chargable headphones but they do have a 3.5mm socket to plug in a cable, so first thing I do is plug in an aux cable to my ipod and audio comes out of both cans so I know it's not a driver gone. then I try bluetooth and sure enough the left side doesn't work when using the bluetooth internal amp. So time to get them apart. I quite enjoy this part, working out how it comes apart without damaging anything. 



So this side we have the battery and the micro USB socket which feeds a lipo charge control circuit. I was expecting the headphone amp to be in this side as well but it isn't. That means it's not the wire passing through the headband that's broke as the headphone amp is the same side as the non working speaker so the headband wire only passes audio through to the right speaker which is working. I'm quite pleased about this as it means the whole headband doesn't have to come apart. 

So left side apart. 



So this is well most of the action is. Here he have a bluetooth receiver with combined amp and volume control. The aux socket has a switch on it so inserting an aux cable kills the BT side of things and routs the aux cable directly to the drivers ..  so first of all I check that's not the issue. That's fine. So I rig up a stereo socket with some fly wires so I can connect some headphones directly to the bluetooth amp module and find the outputs. 

So here's the socket which I've got another pair of cans connected to. First I solder on ground then prod to find my left and right. 



So I find the left and right outputs on the bluetooth PCB and the left output isn't connected to the pad that's got the left output. the build quality and soldering is so shit the vibration alone in the can has pinged the wire off. 

So not a difficult fix and all done now but have to say these things are complete crap. Why or how they can charge £130 for a crap pair of cans with a £10 bluetooth amp in it that's been soldered so badly it breaks all by it's self is beyond me. 

So if you have a faulty pair, do they work both sides with an aux cable ? if they do then drivers are good and your probably find a wire has come away due to vibration, poor soldering and poor design. 

chillidoggy

Still struggling with how to post photos, but I’ve got my late father-in-law’s 1960’s Kenwood Chef in bits at the moment. It’s a weighty beast, built when things were meant to last, and it could well be made from depleted uranium.

Incredibly, pretty much all the parts required are still available through specialist sites, and as I’ve found the problem (a split nylon gear), there’s even an upgrade kit which substitutes it for a steel one, and with two other bevelled gears included to make it quieter in operation.

The online parts and repair manual is 29 pages long, all of it in English, and is comprehensive enough for anyone to completely strip and rebuild the machine, including repairing the electric motor. Deep joy for a tinkerer like me.

Best of all, I now know that the Kenwood company was started by a bloke called Ken Wood. I see what you did there, Ken.

boogieman

chillidoggy said:

Still struggling with how to post photos, but I’ve got my late father-in-law’s 1960’s Kenwood Chef in bits at the moment. It’s a weighty beast, built when things were meant to last, and it could well be made from depleted uranium.

Incredibly, pretty much all the parts required are still available through specialist sites, and as I’ve found the problem (a split nylon gear), there’s even an upgrade kit which substitutes it for a steel one, and with two other bevelled gears included to make it quieter in operation.

The online parts and repair manual is 29 pages long, all of it in English, and is comprehensive enough for anyone to completely strip and rebuild the machine, including repairing the electric motor. Deep joy for a tinkerer like me.

Best of all, I now know that the Kenwood company was started by a bloke called Ken Wood. I see what you did there, Ken.

I bet Googling “specialist sites selling nylon gear” gets some interesting results. 

Danny1969

Ken Wood .... I never knew that, just told the wife but she knew, apparently we have one in the cupboard