JVC RX 7012 VSL - 5.1 surround receiver. It needs a pair of output devices on the left and centre channels. Total cost $7.50 from China. I got this unit for the price of shipping from a guy who didn't want it thrown away, but whose eyesight was so bad he couldn't fix stuff any more. Nice deal.
Very proud of this fix. "No user serviceable parts inside." 
Never stopped me!
What's in those ubiquitous wallwart thingies? Not much it seems. Mine had been dropped.
Transformer (240V to about 12V one supposes), bridge rectifier ( 4X 1nN4001 50V power diodes), 16V 1000uF electrolytic capacitor for smoothing.
Not a hard fix. The capacitor was loose on solder so caused mains hum. Resoldered and glued back together with polystyrene cement and G-clamps. Guaranteed for 5 minutes!
Never stopped me!
What's in those ubiquitous wallwart thingies? Not much it seems. Mine had been dropped.
Transformer (240V to about 12V one supposes), bridge rectifier ( 4X 1nN4001 50V power diodes), 16V 1000uF electrolytic capacitor for smoothing.
Not a hard fix. The capacitor was loose on solder so caused mains hum. Resoldered and glued back together with polystyrene cement and G-clamps. Guaranteed for 5 minutes!
Attachments
Schematics are over-estimated
Not necessarily so.
But of course you joke.
Because working "blind" on some equipment is purely foolish.
I designed and built a model railway reversing loop power phase controller.
Prototype worked great.
Sold 10 with no problems.
Sold another one and he couldn't get it to work, it just kept clicking the relay all the time.
So got it back and found the power supply bridge rectifier is creating spikes on the waveform. The a2d converter is seeing these and assumes a short circuit and flips the relay.
So a triple read of the a2d instead and if all three reads are low assume a short circuit and that fixed it.
I recently bought in a new batch of diodes from ebay and it looks like they spike worse than the previous batch.
Prototype worked great.
Sold 10 with no problems.
Sold another one and he couldn't get it to work, it just kept clicking the relay all the time.
So got it back and found the power supply bridge rectifier is creating spikes on the waveform. The a2d converter is seeing these and assumes a short circuit and flips the relay.
So a triple read of the a2d instead and if all three reads are low assume a short circuit and that fixed it.
I recently bought in a new batch of diodes from ebay and it looks like they spike worse than the previous batch.
Good sleuthing Nigel!
Why on earth would you buy off Ebay??? That one repair cost you a lot more than the difference in price for known good parts.
Hey bucks bunny,
Never go into anything without a schematic if you can get one. It saves you lots of time and you can see iffy design choices at a glance. The first thing I do after checking for simple faults is to get a manual or schematic. That way you can do a proper repair and also set the equipment up if there are any adjustments.
Why on earth would you buy off Ebay??? That one repair cost you a lot more than the difference in price for known good parts.
Hey bucks bunny,
Never go into anything without a schematic if you can get one. It saves you lots of time and you can see iffy design choices at a glance. The first thing I do after checking for simple faults is to get a manual or schematic. That way you can do a proper repair and also set the equipment up if there are any adjustments.
"Why on earth would you buy off Ebay??? That one repair cost you a lot more than the difference in price for known good parts."
If I buy low quantities off RS Components they can be quite expensive.
I thought I couldn't go wrong with 1n4004 diodes. Clearly I can.
I manage to debounce the input in software and that fixed the problem.
If I buy low quantities off RS Components they can be quite expensive.
I thought I couldn't go wrong with 1n4004 diodes. Clearly I can.
I manage to debounce the input in software and that fixed the problem.
Hi Nigel,
My hat is off to you!
You actually had to design your circuit to use defective rectifiers! But, you figured it out and did it.
On the other hand, given that the rectifiers do not act in a normal way, I would be afraid of in the field failures. When a part does not act in the expected way, would that not signal the possibility of other defects?
Isn't there another reasonable option for parts in your area? You worked so hard to design and bring a product to market that it would be a shame for substandard rectifiers to take you down. Then, there is still the value of the price difference from RS Components and the junk, compared to the value of your re-work. Added to that, ? future failures? What are we talking on the rectifiers? How many do you buy, 50? 100? What do they cost?
My hat is off to you!
You actually had to design your circuit to use defective rectifiers! But, you figured it out and did it.
On the other hand, given that the rectifiers do not act in a normal way, I would be afraid of in the field failures. When a part does not act in the expected way, would that not signal the possibility of other defects?
Isn't there another reasonable option for parts in your area? You worked so hard to design and bring a product to market that it would be a shame for substandard rectifiers to take you down. Then, there is still the value of the price difference from RS Components and the junk, compared to the value of your re-work. Added to that, ? future failures? What are we talking on the rectifiers? How many do you buy, 50? 100? What do they cost?
BINGO, Chris!
When it comes to things like rectifiers, anything in the PS area, I refuse to compromise.
It's not worth the justification to scrimp on quality.
And yes, service manuals are a blessing and save time.
This will be a long one... Took my Tesla S out early one Saturday 2 miles away to take care of my friends' cats. Got out and got a message "Voltage too low, car shutting down". Of course the car is recently off warranty. I called Tesla to tow it to the service center. They couldn't arrive until late that evening so I did some diagnostics and came to the conclusion that it was either the 12v battery or it's charging circuit. Tow arrived late and he diagnosed it with the same conclusion. He tried to charge the 12v without success. Then he found that there was no way to hook onto the rear of the car (I pulled in head first into the driveway) and was told by Tesla that he needed wheel skates to hook up. Since he didn't have them, he left me with his business card, told me to call tomorrow, and didn't charge me. The next day I hooked up a trickle charger and came back a few hours later. The battery went from 25% to only 50% and was putting out only a few volts. Decided to order a battery, managed to boot it long enough to put it in tow-mode and roll it downhill to the end of the driveway. The next day my friends came home and asked me to roll it off the driveway a few feet to get it out of the way. So I charged it again, got it into tow mode, rolled it the few feet, but then the car died and wouldn't boot so I could put it out of tow mode. We put some bricks to chock the wheels and charged it for a half-hour before it would boot and I could turn off tow-mode. The weather was going to get bad the same day the battery would arrive (5 days later) so I started prepping it the day before. What were Tesla engineers thinking of? To get the old battery out under the hood you needed to:
Unclip and remove the rear apron.
Disengage 2 hoses from the air duct panel.
Unclip and remove the air duct panel.
Unclip and remove the 3 front aprons.
Remove the frunk liner.
Unbolt and remove the frunk (one end of the battery strap is under the frunk).
Unstrap the battery.
I was just putting the last piece into the trunk when the car booted and was up without any warning messages! I decided to drive it home and garage it. Testing showed that the battery was putting out 13.8v and passed all the tests. Huh? My guess was that there was an internal short that I somehow broke free when I unstrapped the battery. I still replaced it.
A week later I got a software update. Later I went out to the car to find that the driver's side headlight was on. Nothing I tried fixed it including a complete shut-down and boot-up. I did a factory reset as a last resort without success but now my homelink icon was missing and the left blinker didn't "click". Frustrated, I made another appt. with Tesla service. An hour later my wife told me that the headlight was now off. Yup, plus the homelink icon was there and the blinker worked. The only remaining problem is that the car thinks it's on the West Coast while sitting in my East Coast garage. Googling seems to indicate that this sometimes happens after a factory reset and will correct itself after driving a bit. This weekend will tell me if that's right.
I'm convinced that my Tesla is possessed and playing games with me.
Unclip and remove the rear apron.
Disengage 2 hoses from the air duct panel.
Unclip and remove the air duct panel.
Unclip and remove the 3 front aprons.
Remove the frunk liner.
Unbolt and remove the frunk (one end of the battery strap is under the frunk).
Unstrap the battery.
I was just putting the last piece into the trunk when the car booted and was up without any warning messages! I decided to drive it home and garage it. Testing showed that the battery was putting out 13.8v and passed all the tests. Huh? My guess was that there was an internal short that I somehow broke free when I unstrapped the battery. I still replaced it.
A week later I got a software update. Later I went out to the car to find that the driver's side headlight was on. Nothing I tried fixed it including a complete shut-down and boot-up. I did a factory reset as a last resort without success but now my homelink icon was missing and the left blinker didn't "click". Frustrated, I made another appt. with Tesla service. An hour later my wife told me that the headlight was now off. Yup, plus the homelink icon was there and the blinker worked. The only remaining problem is that the car thinks it's on the West Coast while sitting in my East Coast garage. Googling seems to indicate that this sometimes happens after a factory reset and will correct itself after driving a bit. This weekend will tell me if that's right.
I'm convinced that my Tesla is possessed and playing games with me.
I was just lucky/unlucky it didnt show up on the first 10 units.
The software fix works fine so why throw away rectifiers that work ?
They aren't blowing up, just have a little switching noise.
I havent had a return for a blown diode.
In retrospect I should have known of switching spikes having designed lots of amplifiers.
Not so much problems with low voltage but on valve circuits I found i had to use high speed diodes or got 100Hz switching spikes.
The model railway circuit is running at 10KHz so is more susceptible to diode spikes.
The main problem on my part was lazy testing.
I just tested it on DC and of course had no problems.
It really needed a DCC controller to test it properly which I didnt have at the time.
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Do not worry about my way to repair stuff. After decades of practicing I can say that reading schematics often is the 2nd choice. But a visual inspection is my first way to go. Electronics from the nineties often can be traced by eyesight, specially power supplies can be checked by eyesight faster than by reading their schematics. Bad contacts can be found often by simple checks. All in all - I do not negate the usefulness of schematics per se - and of course I am familiar with reading them- but there have been many examples where reading schematics would have been just a waste of time.
I have seen most things with repairs.
I build a lot of new stuff so missed solder joints or even missing components !
Occasional wrong resistor when I havent read parts list properly.
I bought in a faulty Maplin 50 watt amp to repair.
It sort of worked but was distorted.
So did usual visual inspection and it looked fine.
So as it wasnt a huge pcb I checked every resistor, diode and transistor and they all checked ok.
So powered it up again and kept going back to same transistor where voltages seemed strange. I diode checked it again 2bsure and it was fine.
Then it suddenly clicked the diode check was wrong way around for an npn transistor.
It had no number on it as it had rubbed off with age.
Bought the right transistor from ebay as it was obsolete and the amp started working.
Looks like some kind soul before me had tried a repair and made it worse with wrong transistor which was a pnp.
I guess the moral of the story is never assume a component is the right one.
I build a lot of new stuff so missed solder joints or even missing components !
Occasional wrong resistor when I havent read parts list properly.
I bought in a faulty Maplin 50 watt amp to repair.
It sort of worked but was distorted.
So did usual visual inspection and it looked fine.
So as it wasnt a huge pcb I checked every resistor, diode and transistor and they all checked ok.
So powered it up again and kept going back to same transistor where voltages seemed strange. I diode checked it again 2bsure and it was fine.
Then it suddenly clicked the diode check was wrong way around for an npn transistor.
It had no number on it as it had rubbed off with age.
Bought the right transistor from ebay as it was obsolete and the amp started working.
Looks like some kind soul before me had tried a repair and made it worse with wrong transistor which was a pnp.
I guess the moral of the story is never assume a component is the right one.
I'm convinced that my Tesla is possessed and playing games with me.
70K for that thing?
Sounds more like you are possessed.
After reading all the disasters concerning those... vehicles, I wouln't pay a cent for one.
And yet, my 1996 Lincoln MK VIII is still a lovely (and reliable) ride.
Hi Nigel,
Yes, many times previous repairs caused the wrong parts to be installed.
However, I do not use Ebay for repair parts - ever, unless it is an obsolete IC and I have been burned there too. What I do is figure out a current replacement part which I often have, or I order one from a real supplier. Seen too many fake parts, even op amps! For some chips, I turn down the repair as "parts unavailable". Just try to get good uPC1225H for example. I have four lots of these ICs with good markings that are junk.
Hi bucks bunny,
Oh, I can be just as arrogant.
Been doing this for over 45 years and in the 70's there were just house numbered parts no schematics were unavailable often times. Yes, I can often pick out the fault without one, and still have to do that. But. The only way you can ever be sure the equipment is really repaired properly is to have the service information to be sure there isn't a modification or design error. Then, there is setting the equipment up properly.
I am pretty darned good at what I do, and that also means I know I don't know what the designer was thinking every time. I owe it to my client to do a responsible job every time. On a wall-wart, things are so easy you don't need a diagram. With anything more complicated, like an amplifier (for example, most are pretty simple), you should always check. I can't think of any excuse to assume you know more than everyone else and "wing it". The technicians I know personally who are like that each think they are brilliant. They also do not do good work. But damned if they don't believe they are the best technicians out there!
-Chris
Yes, many times previous repairs caused the wrong parts to be installed.
However, I do not use Ebay for repair parts - ever, unless it is an obsolete IC and I have been burned there too. What I do is figure out a current replacement part which I often have, or I order one from a real supplier. Seen too many fake parts, even op amps! For some chips, I turn down the repair as "parts unavailable". Just try to get good uPC1225H for example. I have four lots of these ICs with good markings that are junk.
Hi bucks bunny,
Oh, I can be just as arrogant.
Been doing this for over 45 years and in the 70's there were just house numbered parts no schematics were unavailable often times. Yes, I can often pick out the fault without one, and still have to do that. But. The only way you can ever be sure the equipment is really repaired properly is to have the service information to be sure there isn't a modification or design error. Then, there is setting the equipment up properly.
I am pretty darned good at what I do, and that also means I know I don't know what the designer was thinking every time. I owe it to my client to do a responsible job every time. On a wall-wart, things are so easy you don't need a diagram. With anything more complicated, like an amplifier (for example, most are pretty simple), you should always check. I can't think of any excuse to assume you know more than everyone else and "wing it". The technicians I know personally who are like that each think they are brilliant. They also do not do good work. But damned if they don't believe they are the best technicians out there!
-Chris
Chris, a long ways back, at the repair ship that I worked at, a guy came in looking for a job.
The owner, a kindly old guy, let the guy in to "have a look around".
I was busy servicing a big old Sylvania 23" color set on my bench.
You might know, the ones with the Philips chassis, early/mid 80s.
The guy wandered over, and watched me for a minute, but I continued on with my troubleshooting, my head was deep in what I was doing, and I don't deal with interruptions very well, particularly when they're odd problems.
The guy spoke up, and started babbling on about something, related to his expertise in doing tv repairs - apparently trying to impress me.
I could immediately tell he didn't know crap about servicing tv sets.
So I turned to him and simply said "when you actually learn how to work in a repair shop, maybe then you'll get hired."
The look on his face was priceless.
He never came back, in fact, years later, I heard that after scamming people out of money for his gambling addiction by screwing up peoples tvs and computers, someone beat the crap out of him.
The owner, a kindly old guy, let the guy in to "have a look around".
I was busy servicing a big old Sylvania 23" color set on my bench.
You might know, the ones with the Philips chassis, early/mid 80s.
The guy wandered over, and watched me for a minute, but I continued on with my troubleshooting, my head was deep in what I was doing, and I don't deal with interruptions very well, particularly when they're odd problems.
The guy spoke up, and started babbling on about something, related to his expertise in doing tv repairs - apparently trying to impress me.
I could immediately tell he didn't know crap about servicing tv sets.
So I turned to him and simply said "when you actually learn how to work in a repair shop, maybe then you'll get hired."
The look on his face was priceless.
He never came back, in fact, years later, I heard that after scamming people out of money for his gambling addiction by screwing up peoples tvs and computers, someone beat the crap out of him.
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