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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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28th Nov 2019, 7:26 pm | #21 |
Nonode
Join Date: Aug 2010
Location: Resolfen, Wales; and Bristol, England
Posts: 2,588
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Re: Repair nightmares.
Mine’s a 1980’s synthesiser of the musical variety - it was repaired, sent back the customer who subsequently reported that it wasn’t quite right. Back it came and seemed to be okay until I decided that the main PCB needed a clean. As I’ve done many times before, it went into the dishwasher, came out sparkling but refused to work thereafter …
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28th Nov 2019, 8:19 pm | #22 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Repair nightmares.
Always think strange when faced with seemingly-inconsistent 'repair-fails'.
Mid-80s through to the mid-90s I managed 30 or so sites using X.25 networking and PADs used to connect RS232/V24 serial-port terminals [DEC VT220, Lear-Siegler ADM3A, Tektronix 4010/4014] to various academic/research computer-sites. At one site - sometime early-morning - the PAD would lock-up. There was seemingly no obvious pattern, apart from it always being weekdays and early-morning. The first-line guys were perplexed - so they called me in. I had RF-sniffing loggers and - to cut the story short - one of the temporary staff at the site had a partner who was a taxi-driver. After dropping his missus off he'd fire up his radio and call the office for the first-call-of-the-day - precisely while parked under the twin-twisted-pair overhead cable linking the 'shed' back to the main building. |
28th Nov 2019, 8:28 pm | #23 |
Heptode
Join Date: Feb 2010
Location: Duffort, Gers, France
Posts: 714
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Re: Repair nightmares.
Reminds me of the story of the microwave link that dropped out for a few minutes every morning and evening but otherwise worked perfectly. The engineers could find nothing wrong with it. Then they realized that the beam was just brushing a hilltop. Every morning a farmer drove his cows to pasture and they walked through the beam. Every evening he drove them back home again. Raising the dishes a few feet solved the problem.
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Stuart The golden age is always yesterday - Asa Briggs |
28th Nov 2019, 10:02 pm | #24 | |
Nonode
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,814
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Re: Repair nightmares.
Quote:
Regards Lloyd |
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28th Nov 2019, 11:52 pm | #25 |
Nonode
Join Date: Sep 2017
Location: Stockport, Cheshire, UK.
Posts: 2,000
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Re: Repair nightmares.
While not a repair as such, someone in the same lesson as one of my school friends was bench testing a circuit he had just made on a copperboard, & had the good idea to hold it steady in a vice.
When power was applied there was a fireworks display of blown components as the vice short circuited the entire assembly, much to the annoyance of the teacher taking he lesson.
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29th Nov 2019, 1:41 am | #26 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
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Re: Repair nightmares.
When I was an apprentice running a flip top Murphy on its side and the oil filled lopty exploded sending oil everywhare , I cannot remember the orignal fault.
Things were so diffrent then. |
29th Nov 2019, 1:48 am | #27 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
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Re: Repair nightmares.
I have always found laptops to be nightmares.
They are the ultimate rubber job. They bounce like those "super balls" you used to be able to buy in the early 1970s. |
29th Nov 2019, 2:20 am | #28 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
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Re: Repair nightmares.
Post 24 reminds me of a manufacturer's service advice on a popular, worldwide-selling audio amp which had a mostly SMD main board. The glue dots under each and every component had, with age, turned conductive.
Rather than remove the parts, the high impedance areas were modified to pass slightly more current to mask the problem in critical areas. It's lucky I was privy to the service advice otherwise I'd have been stumped on several occasions, as the faults would usually be intermittent.
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Kevin |
29th Nov 2019, 8:01 am | #29 |
Dekatron
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
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Re: Repair nightmares.
I've come across the test lead snafu, I use a homebuilt dummy load with 3 BNC's on each channel, one for a scope, one for a DMM etc, and on several occasions I've had either low OP from an amp or no OP. I chucked several BNC leads before sussing the problem. The resistors sit on one big heatsink, which is a tunnel type with a big fan on one end, this is mains powered and had an earth crimped to the body of the HS, there must have been an earth loop.
I've tried to fix a few Iphone's, getting the minute screws back in afterwards is highly problematic, they also seem to have been crossed with Mexican jumping beans, often leaping several feet off the bench. I've spent many happy hours searching the floor whilst being berated by my daughter "Is my phone done yet". Needless to say the Iphone had less screws in it everytime I put it back together. Talking of screws why do you always have at least two left over after you take something apart no matter how careful you are? A.
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29th Nov 2019, 8:04 am | #30 | |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
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Re: Repair nightmares.
Quote:
In fact, after all the intermittent and frankly diabolical faults I have had to repair in a lifetime, I'm surprised I'm not curled up under a tree in a local public park clutching a brown paper bag with a whisky bottle in it. So you are in good company. |
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29th Nov 2019, 11:00 am | #31 |
Heptode
Join Date: Apr 2016
Location: Cheltenham, Gloucestershire, UK.
Posts: 872
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Re: Repair nightmares.
Quite frankly, I'm surprised that you remember ANYTHING after an event like that mate!
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29th Nov 2019, 11:10 am | #32 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
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Re: Repair nightmares.
Repairs are relatively easy and straight-forward...
. . . . compared to some customers. Some other customers were wonderful, though. I suspect we saw a similar spectrum of humanity at dad's garage as the radio/TV trade had to deal with. David
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29th Nov 2019, 4:19 pm | #33 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Repair nightmares.
Quote:
which was often either on something utterly unrelated to what our support-contract covered (often on equipment supported by my competitors - or not on any sort of contract at all) or if it _was_ something covered under contract it would be of a nature and complexity several times greater/needing much more time than the original fault-call. One particular taxi/courier company was really bad at this: you'd go to head-office to replace an intermittent base-station microphone - jobsheet-time 30 minutes+travel - then the "While you're here" would be to look at one of their drivers' radios. Of course you'd been listening to the base-station radio and the drivers chatting while you'd been doing the initial job - and knew that the driver in question was at least 20 miles away. |
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29th Nov 2019, 4:54 pm | #34 |
Octode
Join Date: May 2003
Location: Belper Derbyshire
Posts: 1,910
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Re: Repair nightmares.
I had a silly one a few weeks back at work. One of the 3 phase pump motors kept tripping its overload and blowing the black phase fuse that also protected it. After using a current clamp and meggering it (insulation 680K, so not brilliant), it still intermittently blew the black phase fuse I decided that the motor was at fault and changed it over dropping it on my thumb in the process!! After replacing the motor it did not work at all and I found out that the replacement motor that was on our shelf was also faulty (O/C windings) and a third motor was tested ok and fitted.
I came back to it later only to find the fuse had blown again. After a lot of head scratching I discovered that someone in the past had wired up an old engine cooling heater to that phase between the fuse and the 3 phase pump contactor (which was not on any circuit diagram and buried in the bottom of a control cabinet) which had a broken element which was causing the black phase to blow in the first place. This was causing the pump when it started to try and run on 2 phases, stall and then trip its overload. Christopher Capener
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29th Nov 2019, 5:56 pm | #35 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
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Re: Repair nightmares.
Out of interest I did once attempt to repair one of my Daughter's cast off ipods. By the time it was unglued it was apparent that it wasn't designed for repair, so it wasn't and no longer exists.
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29th Nov 2019, 7:34 pm | #36 | |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,706
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Re: Repair nightmares.
Quote:
David |
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29th Nov 2019, 8:11 pm | #37 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Repair nightmares.
Quote:
Instinctively, I swapped the smoothing-electrolytic in the power supply. No difference! A scope on the power-rails showed an acceptable ripple level. I was starting to think about leakage between the windings in the mains-transformer when I noticed the flaking black paint on the glass case of the front-end transistor [OC44]. Yes, it was playing the phototransistor-game and the fluorescent-tube bench-light was wobbulating the local oscillator. A bottle of Tipp-Ex came to the rescue. I'd quoted a price based on half an hour to replace the volume-control; I'd now spent at least 2.5 hours on it. No profit there! |
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29th Nov 2019, 9:53 pm | #38 | ||
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: Repair nightmares.
Quote:
Thermistors and EPROMs score highly. |
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29th Nov 2019, 10:32 pm | #39 |
Banned
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
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Re: Repair nightmares.
My worst has been when toroidal transformers first became available. I had made a "stonkin" guitar amp using 4 KT88's. It worked superbly. About three weeks after I sold it, it returned. SHORT circuit primary winding inside toroid. Air freight new transformer from Sydney. Fit transformer. everything working perfectly. bench test, doing everything I could think of to "blow it up". Nothing worked. Delivered amp back to customer. Four days later I get an ( angry) phone call. Same thing, it doesnt work. I drive 140 kliks out to the farm where the amp is used. Customer leads me to a shed some few hundred yards from the house? Why is the amp out here? "Missus cant stand the noise".
Inside the shed is an ANCIENT Lister/Petter diesel generator. Two black wires lead from the generator to the amp, via an uninsulated power socket. No earth!! No earth on the generator!! I ask the customer to start the generator. It runs well with its 50 years of leaked oil everywhere. BUT its doing about 1300 revs, NOT 1500 revs. I speed the generator up, take amp back and unwind the toroid. It has an insulation arc that has completely cut the wire in two about half way along the primary. Order another toroid. That amp only cost me $1300 to repair. I origionally made $800 profit. Joe |
30th Nov 2019, 12:07 am | #40 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
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Re: Repair nightmares.
My father told me a story about a bag sealing machine in the 1960s when they were very special indeed.
They got it working perfectly in the workshop with the new safety sensor to stop you putting a hand in. Come demo day and the covers went on and the thing tried to seal the reps hand into a plastic bag. They had handled the board too much and the paint was chipped on the OC series transistors. |