My kettle fix lasted 10 minutes, and I had to put my hand in my pocket and buy a new one. £25! This is outrageous. 
More luck with my dodgy old £30 Sony amplifier. Kept losing the right channel. Take off 4 case screws and spray volume control with aerosol switch cleaner. Excellent.
And on a roll with dodgy freebie bike with locked up handlebars. New stem ballraces for £5. Old ones had rusted. All greased and set up to go faster. I always forget to put on handcream before these jobs, so filthy nails for the next week.
More luck with my dodgy old £30 Sony amplifier. Kept losing the right channel. Take off 4 case screws and spray volume control with aerosol switch cleaner. Excellent.
And on a roll with dodgy freebie bike with locked up handlebars. New stem ballraces for £5. Old ones had rusted. All greased and set up to go faster. I always forget to put on handcream before these jobs, so filthy nails for the next week.
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Back when they built things to last...
Edit: Just realized I replied to a rather old post.
I fixed a transistor matcher design.
It wasnt displaying correct Hfe on high gain transistors.
I was calculating the base voltage by looking at other side of base resistor.
Didnt take into account base voltage at transistor can vary as its driven harder.
Seems to be worse for high gain transistors.
Fixed it by adding a differential amplifier across the 1k base resistor to measure base current. I know collector current so simply Ic/Ib = hfe.
It wasnt displaying correct Hfe on high gain transistors.
I was calculating the base voltage by looking at other side of base resistor.
Didnt take into account base voltage at transistor can vary as its driven harder.
Seems to be worse for high gain transistors.
Fixed it by adding a differential amplifier across the 1k base resistor to measure base current. I know collector current so simply Ic/Ib = hfe.
A multimeter I bought when I was still a university student many, many moons ago. The make is TES 2360 SCR. This nice chunky multimeter, besides being quite rugged, can measure:
a) inductance (5 ranges)
b) capacitance (5 ranges)
c) resistance (6 ranges)
d) diode test giving the forward voltage at 1mA
e) TTL probe
f) frequency from 0 to 4MHz
g) temperature both in Celcius and Fahrenheit. The probe consists of a diode fed a constant current. The voltage across the diode depends on the temperature, but with a negative gradient of about -2mV/C
h) Voltage both AC and DC up to 1000V DC and 750V AC
i) Current both AC and DC up to 10A
The malfunction was caused by dry joints: pads seem to be too small and the through hole component wires were trimmed too short. I had to very very patiently remove the previous soldering and resolder many pads. There are two PCBs.
I have yet another multimeter which I bought with the first money I earned waiting for its term to be opened and meticulously repaired. However, this second multimeter has scratches cutting through the entire thickness of the PCB tracks which serve as the contacts for the rotary switch. The scratches are caused by the contact springs, so I have to find another way instead of using the original springs. Admittedly, this will not be easy.
a) inductance (5 ranges)
b) capacitance (5 ranges)
c) resistance (6 ranges)
d) diode test giving the forward voltage at 1mA
e) TTL probe
f) frequency from 0 to 4MHz
g) temperature both in Celcius and Fahrenheit. The probe consists of a diode fed a constant current. The voltage across the diode depends on the temperature, but with a negative gradient of about -2mV/C
h) Voltage both AC and DC up to 1000V DC and 750V AC
i) Current both AC and DC up to 10A
The malfunction was caused by dry joints: pads seem to be too small and the through hole component wires were trimmed too short. I had to very very patiently remove the previous soldering and resolder many pads. There are two PCBs.
I have yet another multimeter which I bought with the first money I earned waiting for its term to be opened and meticulously repaired. However, this second multimeter has scratches cutting through the entire thickness of the PCB tracks which serve as the contacts for the rotary switch. The scratches are caused by the contact springs, so I have to find another way instead of using the original springs. Admittedly, this will not be easy.
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Not so much a repair as a modification.
I changed 50VA VPT12 to 100VA VPT18, swapped 6P36S for 6P45S, and changed some values in the phase splitter.
Happy me.
My camera sure shows the dust in this place... They are building 4 condo towers within 200m of here - it's so dusty all the time!
I changed 50VA VPT12 to 100VA VPT18, swapped 6P36S for 6P45S, and changed some values in the phase splitter.
Happy me.
My camera sure shows the dust in this place... They are building 4 condo towers within 200m of here - it's so dusty all the time!
Attachments
Had to fix one of my own screwups yesterday. Taking apart an original Bose Wave Radio that a friend bought at an estate sale, I didn't discover until too late that the internal AM rod antenna had a piece of foam cushion glued across the top that had become mired to the upper section of the enclosure over time. As I separated the sections, the rod was pulled out of its plastic base, and all 4 coil wires ripped loose from their terminals before I even knew what was happening.
After carefully peeling the rod and its dangling leads from the inside of the plastic enclosure, I stared at it for a minute. Not being a radio guy, I knew there was a big coil and a smaller one but that's about it. Luckily I was able to find a schematic online, and after a bit of studying & probing I got it right on the first try! (This is great, because I get ice cream when this happens.)
Sadly the original symptom (very dim display) persists. No bad capacitors in the circuit; the fluorescent module is just shot, replacements are extinct. Oh well.
After carefully peeling the rod and its dangling leads from the inside of the plastic enclosure, I stared at it for a minute. Not being a radio guy, I knew there was a big coil and a smaller one but that's about it.
Luckily I was able to find a schematic online, and after a bit of studying & probing I got it right on the first try! (This is great, because I get ice cream when this happens.)Sadly the original symptom (very dim display) persists. No bad capacitors in the circuit; the fluorescent module is just shot, replacements are extinct. Oh well.
Electrolux vacuum cleaner
Repaired a faulty bagless vacuum cleaner which was not a very old device at all. Started to sound like if there was someone inside welding something during the first couple of seconds. Turned out to be one carbon brush almost completely depleated and crooked. Original spare carbons are non-existant, but the new motor they offer for sure so I went on a hunt to find similar ones and I found some. Cleaning commutator works wonders.
Repaired a faulty bagless vacuum cleaner which was not a very old device at all. Started to sound like if there was someone inside welding something during the first couple of seconds. Turned out to be one carbon brush almost completely depleated and crooked. Original spare carbons are non-existant, but the new motor they offer for sure so I went on a hunt to find similar ones and I found some. Cleaning commutator works wonders.
I am not claiming that my efforts to improve the World are the best.
But no lack of effort.
I could blame my local Council for pathetic effort on Dark Skies. What Idiot installed that awful blue light on the Flats next door?
Anyway, good gardening this afternoon. Looks tidy. My neighbours congratulated me.
You can contact the council and say that the stray light is keeping you awake at night. Extra points if you mention babies being kept awake. They an put a shroud over it to not shine over the boundary. Same with street lights.
I built up a USB interface.
When I plugged it into my pc it had a hissy fit and told me the device had a problem.
Had a look around on the pcb and had accidentally shorted D+ and D- on the USB interface.
Built up another one and that had a problem too.
Turned out I had shorted SMD processor VSS and VDD pins together with solder bridge.
Need a smaller tip soldering iron tip !
When I plugged it into my pc it had a hissy fit and told me the device had a problem.
Had a look around on the pcb and had accidentally shorted D+ and D- on the USB interface.
Built up another one and that had a problem too.
Turned out I had shorted SMD processor VSS and VDD pins together with solder bridge.
Need a smaller tip soldering iron tip !
Replaced a bad screen resistor that opened when the screen became the only anode (the wire to the top cap was poorly soldered) to get the amp going again.
A push pull amp with only push doesn't sound all that great LOL
Now on to replacing the cathode resistors in my monoblocs for surge rated parts.
A push pull amp with only push doesn't sound all that great LOL
Now on to replacing the cathode resistors in my monoblocs for surge rated parts.
Repaired two faulty (but not dead) ATX power supplies for my colegue. One had faulty (bad or very bad) almost every electrolite capacitors and a bad fan. Changed them all and now it works like new.
The second one fortunately had only faulty mains switch. It had lost a contact. Changed it and some tired electrolites to polimer ones.
Now have a third one dead ATX power supply with a short-circuit at the input (it seems to me it is 5VSB MOSFET problem). This one will be harder to repair.
The second one fortunately had only faulty mains switch. It had lost a contact. Changed it and some tired electrolites to polimer ones.
Now have a third one dead ATX power supply with a short-circuit at the input (it seems to me it is 5VSB MOSFET problem). This one will be harder to repair.
I had a hash noise on a tube phono stage I built that was powered from SMPS.
After trying to filter it with chokes and caps etc, I ended up just using an MIC29300-12BT on the output of the 12.6V supply driving the DC DC board to clip off the noise. Because the DC boost is dumb, it effectively amplifies the noise but only with the added gain of the phono could you hear it. No more
After trying to filter it with chokes and caps etc, I ended up just using an MIC29300-12BT on the output of the 12.6V supply driving the DC DC board to clip off the noise. Because the DC boost is dumb, it effectively amplifies the noise but only with the added gain of the phono could you hear it. No more
My last “repair” and I put that in inverted comas, was a NAD D1050 DAC and headphone amp. It runs off a 5V wallwart and the owner had inadvertently plugged 22V into it. Only for a shot time and just a little smoke were the comments. Luckily, the protection circuits had kicked in, the only casualties I could find were an electrolytic and a 3.3V regulator. With these changed the unit came to life, all test points showing the correct signals except the touch panel would not work and I could not select audio. Rather foolishly I thought a firmware upgrade might fix the problem. This loaded but failed to initialise and the unit is now good as dead, Anyone who has an idea how to unbrick these things your thoughts would be much appreciated.
