This is my third Mega component tester – I keep dropping or breaking them. I find them to be a pretty much indispensable tool. I see there are perspex covers available on eBay, but when I got my latest one I looked around for something to put it in. Cassette case! I cut away part of it with my soldering iron (mmmm, fumes!). The 9 Volt battery was too thick to fit in the case, so I cut away part of the rear, padded the interior with draught strip and taped it all together with clear tape. Four stick-on equipment feet, and – voila! So professional…not! Feels remarkably solid, compared to how fragile and vulnerable it is without a case.
I got this to repair because it was dead as a doornail. I like that expression. It has an inexplicably surreal quality. I tested lots of things, mostly in the power supply area. Almost immediately after the AC line entered the amp it measured 140V, and I couldn’t figure out why – something must have been pulling it down. I tested components on the two power supply boards and the transformer primary and secondaries were fine. A couple of days later I was having another look at it and a penny dropped – I remembered a Yamaha RX-E810 Pianocraft receiver I’d worked on. I tested the 22nF 630V metal film capacitor across the AC line, it measured 4.3nF, I replaced it – and the receiver powered up. Amazing. Go to the head of the class…apparently this is a very common problem with these units, as the internet advises.
I got this to repair because the left channel dropped out when the tone controls were selected – this receiver has a switch to bypass the treble and bass. I (foolishly) took the customer at their word and opened the unit up and started testing things. ALWAYS TRY THINGS OUT FOR YOURSELF! I tested all the components on the tone control and flat amp (that’s the one with the volume control mounted on it) boards and lubricated all pots and switches thoroughly. The thing I usually mess up: I was removing transistors, the pinouts were marked on the top of the PCB, I removed a transistor then realised it was a FET and I hadn’t noted the orientation. G$$%^&mmit! I always do this! But I put it in my trusty (I thought) Mega tester and identified the pinout, matched it with the pinout on the PCB and Bob’s etc. BUT…nothing! No sound from amp…back to drawing board. A couple of days later, I removed the FETs and found that if I tested them, then reversed them in the Mega tester’s ZIF connector – I got the same pinout! I guess there’s a bug or inconsistency in the Mega tester with regard to FETs! I looked up the pinout in my transistor guide (invaluable, and, inexplicably, no longer available), installed them – and – NOTHING! A closer look revealed one of the wires from the power supply to the protection circuit board had broken, so I CHECKED where it went, resoldered it and the mighty beast powered up and sounded AWESOME and NOW I WANT a ’70s silver-faced receiver. For heaven’s sake…NOTE ORIENTATION BEFORE REMOVING COMPONENT! I should have it tattooed…on the inside of my eyelids!
This had a blown fuse in the left channel and one of the flying saucer transistors in the right channel was half-dead. There was signal but it was distorted and leaking from the right channel into the left channel output, strangely. I replaced the 8002-1 and 9002-1 driver transistors with BC639 and BC640. All was working well, the owner collected it but I got a call from him that evening. Apparently it had worked well for about half an hour then started hissing from the left channel, not volume-dependent so I assumed it was in the power amp. He returned it, I replaced the two remaining flying saucers but it didn’t fix the problem. I tested, replaced or substituted all the capacitors and semiconductors in the left channel of the power amp, excluding the power transistors – I could hear the hissing in headphones, so I assumed the faulty component was somewhere before or including the driver stage, as the headphone jack is fed from there. A bit of reading suggested the fault might be on the preamp board, but after the volume control. I replaced the famously noisy transistors in the preamp with two BC549 and two 2SC2240 when I ran out of the former. I had to redo this as I hadn’t paid close enough attention to the orientation of the ones I removed, which were in an unusual package. So, consulting the schematic I managed to get them in and the preamp working. This is a theme which will continue throughout the weekend, dammit. I seem to be getting dumber with age! So I powered up the amp, all good for a few minutes – behold, the noise reappeared but in the right channel this time. I pressed on the huge, telephone-part-looking connector from the main board to the preamp, and the noise went away! I resolved to remove the connector and solder the wires direct to the preamp board. I undid the connector, drew a diagram of the layout and started removing the wires. After a while I started to realise that I hadn’t been exact enough about the layout or orientation of the connector, and hadn’t taken pictures. Sooo…a couple of hours later I managed (with the help of the schematic) to get it all connected properly. And fortunately didn’t cook any other components in the process. What’s the lesson here? NOTE ORIENTATION BEFORE REMOVING COMPONENT! TAKE PLENTY OF PICTURES! The thing that tripped me up was, there were two possible ways for the socket to fit into the PCB and I hadn’t carefully noted which way it had been installed. There were two pins which had been cut off, even though there were wires soldered to the tags for these pins. I had soldered these wires to the corresponding holes in the PCB, but on the second-to-last attempt there was still no signal coming through. I realised these wires were just shorting the 12V preamp supply voltage to ground, so I lifted them and all was well. I sometimes wonder if I just do things carelessly to make more interesting problems for myself. The way I ended up doing the job, I gained a much closer understanding of how the circuit works and got practice at reading a schematic. I suppose the only concern is, if I’m trying to make money doing this, unproductive time is best avoided. I’ve seen a few internet postings about noise in one channel of the AU-555A, but nobody has mentioned the possibility that the connector is one of the culprits. I’d tried using contact cleaner on the pins and refreshing the solder joints, but the hissing continued. Best to remove it completely, I think.
So I buy broken iPhones, fix and sell them. I recently purchased a white 5S which was supposedly working fine except for a broken screen, NZ$71. The housing was dented quite badly near the sleep/wake button (to use the correct Apple terminology) and the touch ID didn’t work. I took the logic board out of the housing and tried straightening the housing, but despite being careful fractured the plastic link between the main housing and the top end. I always manage to do this! Actually I’d rather replace the housing than attempt to straighten it when it’s quite bent, sorry Louis Rossman. I hunted through my used housings and chose the best one, a vivid gold colour, transferred the components, reinstalled the OS – actually updated to iOS 11, d’oh! – and put it on Trademe. I noticed that it would be dead by morning, then it wouldn’t charge, so I bought a new battery and it charged fine. Meanwhile I sold it, and then noticed it was still running down completely after 4 hours. I told the guy all this when he came to collect it, he left it with me and I put my SIM in to test the phone out. I didn’t think the problem was symptomatic of U2 disease. It would charge properly, or so it seemed, but it kept going flat after 4 hours use, and it would last all night on standby but be at 5% by morning. I bought a black 5S with a broken screen, and rather than order a new screen I put the logic board into the gold housing, and the same thing happened. The phone would run completely flat after 4 hours of moderate use. I did all the turning off people recommend on the internet – background app refresh etc. – but no joy. The buyer passed on the trade after I gave him an update, and tonight I tried putting the black 5S logic board back in its original black housing. I was just reading something which talked about poor cellular reception contributing to battery drain, and my workshop is in an absolute black spot, so I’m wondering if that has anything to do with it. But I’m noticing the black 5S has been sitting on 72% for the last half hour and wondering if the housing can contribute to battery drain. I changed the charging flex in the gold housing because I’d read that a short in that can cause battery drain. I wonder if something like a burr on the interior of the housing or something like that can cause a short. I made sure all the connector foam pads were present (they weren’t) because somebody said that contributed to battery drain. So I’ve turned the place upside down trying to fix this. I guess there could be some component on the logic board causing drain, but the same thing happening with two different logic boards? The housing is the only thing in common – different boards, batteries and charging flexes. Or maybe it’s iOS11…watch this space!
So a couple of weeks have gone by, I put the original logic board into a new aftermarket housing and used the phone with a SIM installed for a couple of days. I’d get about 3 1/2 hours use before the battery was flat. I realised on Sunday that the housing wasn’t the only part I hadn’t changed, so swapped the front camera/proximity sensor/ambient light sensor/ear speaker flex, the ear speaker and the metal screen shield – and, lo and behold, the phone now lasts all night on standby, a solid 8-9 hours of use on a charge – amazing! It’s been sitting on around 94% for the last 4 hours, Wifi on, background app refresh off and no mail account installed. Which is not a lot of drain, but in the past the charge would have gone down like a cartoon cigarette. Amazing. It may now be saleable. I realise this isn’t on the same order of phone fault diagnosis as “short on VCC main” or “replace Tristar” but the proof of the pudding, as they say, is in the eating…I thought it was Tristar for a while, but it has none of the symptoms of Tristar fault, as far as I can make out – no fake charging, it will charge from a drained battery etc.
I’d bought this years ago, purchased a new housing from eBay and installed it then set the phone aside until recently. I sold it on Trademe THEN did some testing to make sure it was OK! It wouldn’t recognise SIM cards. The SIM tray had no missing contacts, so I removed the antenna cover at the base of the phone, noticed the cable wasn’t plugged in properly, there was a component next to the cable which had come loose at one end, and remembered I’d replaced one of the three connector ‘prongs’ on the motherboard with a piece of wire which REALLY wasn’t doing its job. I resoldered the component (microsoldering always stresses me out!), removed my wire connector and scavenged a replacement ‘prong’ from another phone board and soldered it in place. Phone back together, it now connects to the network but the microphone seems faulty – I’m almost inaudible in a call. One of the things I’ve had ZERO success with to date is replacing Nokia microphones. So it was with understandable trepidation that I removed the motherboard, set it up in a phone repair vise and got out the rework gun. I set it at 375 degrees and applied heat to the underside of the board just below the mic. It lifted off after a few seconds. I put fresh leaded solder on the board traces, added Amtech flux then positioned the new mic in place. Set the gun at 350 degrees, applied heat to the underside of the board once more. The mic was moving around a bit so I turned the air speed down and helped it stay in place with tweezers. After a few seconds I could see it settle as the solder melted. I turned off the gun, let the board cool down then cleaned it with isopropyl alcohol and toothbrush. I reassembled the phone, and, amazingly enough, the microphone worked! I called my flatmate Holly who had been putting up with test calls earlier, and she reported it sounded much clearer and louder! A win – and my first successful replacement of a Nokia microphone. Yay!
Friend Martin brought me his Pro-ject Debut (I’m not sure which iteration) because the platter had begun rotating counter-clockwise. We plugged it in and it spun clockwise, then I turned it off and on again and it spun anti-clockwise. Troubling! The only other turntable I’ve encountered this with was a Dual 505. The phase shift cap goes bad over time and this causes the reverse rotation. I didn’t think this would apply as it’s a recently produced turntable, but I had a look at what I assume is the phase shifter cap. It was marked 8.2uF, measured 12uF. ESR and voltage loss seemed OK. I replaced it, wondering if that would have any effect. But it didn’t – still rotating counter-clockwise. There’s a diagram on the motor explaining something – it took me a while to figure out what. There are four wires to the 16V AC motor: yellow; white; red; blue. The diagram depicts the two motor coils as resistors, and shows how the AC is connected to them: the yellow and white are ‘common’, the red and blue are ‘active’. In order to change rotation direction, the ‘active’ wire from the on/off switch can be connected to either the blue wire or the red wire. There’s also a 2.7nF ceramic cap, which I assume is for on/off switch spark suppression and is connected across the switch. Initially I’d just swapped the red and blue wires, this caused the rotation direction to change but created vibration (not good!). I swapped the wires back, then worked out what the diagram was driving at. I attached the ‘active’ AC wire to the blue wire’s lug and the motor began rotating clockwise. Strange that it had been wired the other way and had rotated clockwise until just recently. Problem solved…
Here’s the motor with wiring diagram…disturbing it took me so long to work out what it meant!