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Old 15th Dec 2019, 8:15 pm   #161
G6Tanuki
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Default Re: Repair nightmares.

I re-soldered all my cheap croc-clip leads, and also fitted a short length of red heatshrink on the wire, as a reminder that I'd done a particular lead. That way, if I ever buy any more I'll know which ones need resoldering and which I've already done.
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Old 15th Dec 2019, 10:33 pm   #162
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Default Re: Repair nightmares.

I have spent my working life repairing electronics in hospitals. The repairs aren't the nightmare just where the equipment is. Think of intensive care units, A&E, maternity or baby care units. Dealing with non working kit next to a patient on a ventilator, or an ECG monitor attached to a pre-term baby.
When I retired I was repairing cancer treatment machines. More pressure to keep them working as they treat patients from 08:00 to 20:00 Monday through Friday and occasionally weekends.
If I made a mistake then patients could miss their treatment.

|Malcolm
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Old 16th Dec 2019, 5:53 am   #163
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Default Re: Repair nightmares.

Back in another lifetime, I worked at a Broadcast Maintenance Depot.
This was run by Telecom Australia, who for their sins, looked after the TV & Radio transmitter sites for the Australian Broadcasting Corporation.

Most country sites were unattended, with the local Telephone Techs doing "first-in maintenance".

For more complex stuff, two Techs from the Depot, either jumped into a van , or if it was a long way away, took an airline flight to the site.
We received a complaint from the "first-in" guys that the 'modulation monitor" was reading high, in fact, going off scale on modulation peaks.

We duly grabbed a spare Mod Mon of an older type, checked its calibration & sent it off, only to be told " It's doing it, too!".
In the meantime, the original had arrived at the Depot, been checked, & proven to be "in spec".

The Boss, at that point sent me & another bloke off to investigate.
When we arrived, about 3 hours later, sure enough, there was the meter "pinning" on modulation peaks.

What the hell?
Looking around, our eyes fell upon a BWD Oscilloscope which probably hadn't been used since the site became unmanned---but luckily, it worked!

We hung it off the RF monitor point instead of the "mod monitor", & were confronted by a classic overmodulation scenario, carrier cutting & all.
Swiftly reducing the input fader for the Tx fixed it in the short term.

It turned out that the "local" techs had lined the thing up with tone at +8dbm, instead of +16dBm (the former being a common lineup level in telephony equipment).

When programme, was returned after their lineup, it was 8dBm higher, causing the observed problem.
Interestingly, there was no apparent effect upon sound quality during casual listening.

The original mod monitor was refitted, the audio lineup done correctly, & additions in red pen were made to the lineup instructions emphasising that lineup level was +16dBm.

The fault wasn't all that hard, but the "nightmare" was the fact that a transmitter under our care was probably producing "sprogs" every 531 kHz across the MF band & beyond!
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Old 16th Dec 2019, 9:24 am   #164
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Default Re: Repair nightmares.

If you get involved in design and development, you do a design and get a board laid out. For RF designs, you often lay it out yourself because layout can be much more critical. A prototype board gets made and loaded, then you get to crank it up and try it out.

Getting it going is very similar to a repair job. Hand assembled by someone who can never have done one like it before gives a risk of mis loaded components. Then there is the possibility of design errors which could be at a detail level or even down at the fundamental concept level.

This makes it a repair job from hell. You don't have the knowledge that this board used to work. You don't even know that any board to this design has ever worked. You're looking at the only one. Oh, and there's a definite date in the project plan it's needed to be working by. Someone, somewhere is keeping tabs on how much sales/production money will be lost for every day it is late. No stress, then.

It's a different world to handling repairs that come in from consumers, but the loss of knowing it once worked hacks away some of the foundations of normal fault finding.

I once got it in the neck over a prototype board which seemed completely dead. It turned out that the contract assembler, a large multinational one, had bought fake amplifier chips. Well, they had AD811 written on the right size package. I didn't get any apology afterwards from the manager who'd blown his top. It worked fine with real parts fitted.

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Old 16th Dec 2019, 10:58 am   #165
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Default Re: Repair nightmares.

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Originally Posted by Radio Wrangler View Post

I didn't get any apology afterwards from the manager who'd blown his top. It worked fine with real parts fitted.

David
The problem is that often folks in management in the electronics industry have a knowledge of electronics that is diaphanous, or easily that thin. So they over simplify problems in their own mind.

I once was discussing some technical issues with management. One fellow remarked, well at least in your line of work, fixing broken equipment, it must be pretty easy. I said, Why would you say that ? The reply: You just follow the wires and see what's wrong.
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Old 16th Dec 2019, 12:42 pm   #166
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Default Re: Repair nightmares.

Not exactly a repair, but I worked in a TV facilities house in the Eighties. In those days an Arriflex film camera was linked to a Nagra tape recorder using a sync lead. A pop programme came in where it was clear the cameraman had forgotten to connect the lead, so that the lipsync was out after a second or two. Worse, it was due for transmission that evening! I spent a fraught afternoon with the editor manually synching the sound to vision, coupled with lots of cutaways to the audience. Finshed just in time for transmission.
I was very pleased with the result, only to be brought in front of the manager who told me in no uncertain terms I should have refused to do anything as it was the production company's fault and could have reflected badly on us if it had gone wrong.
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Old 16th Dec 2019, 1:40 pm   #167
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Default Re: Repair nightmares.

The move from design to production can be frustrating: one piece of kit I was involved in used numerous small diodes - the kind with a pale blue body and coloured bands, looking like tiny shiny resistors.

Design units worked just fine - then the boards were put into production.

Of the first thousand produced, only about 20% worked. Much head-scratching over a weekend, followed by an angry email-exchange with the production-contractor.

To cut a long story short, I found that a bunch of the diodes - fitted in the same place on every defective board - had the printed markings on the body reversed.

The production-contractor then had a heated exchange with his component-supplier!
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Old 16th Dec 2019, 2:01 pm   #168
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Default Re: Repair nightmares.

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In those days an Arriflex film camera was linked to a Nagra tape recorder using a sync lead.
When I first saw the capstan speed control circuit in the Nagra MK2 tape deck I was very impressed. It would also lock to a crystal reference that was an on board option. The genius of it was, the phase detector for the servo was a 4 quadrant multiplier circuit, with crossed collectors, like the MC1496 IC, but made with discrete parts and oddly, it pre-dated the patent for the "Gilbert Cell" even though it was the same circuit (so the patent lawyers either didn't know what they were doing) or were unaware that Nagra was using it. The configuration was invented by a fellow named Jones.

One of the oddball items in my collection of stuff is a new old stock Nagra MK2 tape deck. I only used it once to check it was operational. I have just held onto it as a reminder of the distant days when I once repaired these recorders for a Film company. The lip sync was always a big issue back then.
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Old 16th Dec 2019, 2:11 pm   #169
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Default Re: Repair nightmares.

We had a similar experience at Plessey in the 1970's. It was a radio receiver for use in a guided missile, and the VCO assembly had to be encapsulated in electrical-grade Araldite of closely-controlled dielectric constant to cope with the vibration. As the presence of the Araldite affected the effective inductance of a printed circuit inductance used in the phase-locked loop, testing could only be carried out after encapsulation. The lab prototypes had worked fine, but none of the batch of 20 made by the prototype shop worked, much to the concern of our highly skilled and normally utterly reliable operatives. After removing the Araldite (no easy task) the fault was eventually traced to a zener diode. While the polarity markings of all those in the batch were correct, their zener voltage was not as marked. This was all the more inexcusable as we had gone to the not inconsiderable expense of having all the components 100% screened for compliance with specification in accordance with a stringent Mil Spec.

Re the patent issue, this is not uncommon. After leaving Plessey I became a Patent Examiner with the UK Patent Office, and granted a number of patents relating to circuits that I had used at Plessey but for which details had not been published, mainly because they were used in military equipment. At the time I joined, technical journals used to be circulated to examiners, and the acquisition of relevant text books was encouraged, even though the then-current patent law only required the examiner to search UK published patents. By the time I left in 1989, the emphasis was on efficiency ( ie cutting costs) and the collections of non-patent literature that examiners such as myself had carefully built up were ordered to be disposed of when the Patent Office relocated to Wales, on the ground that there was no space in the new improved office to accommodate them. This was despite the fact that the legislation then in force did (optionally) provide for non-patent literature to be covered by the examiners' searches.

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Old 16th Dec 2019, 2:27 pm   #170
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Default Re: Repair nightmares.

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oddly, it pre-dated the patent for the "Gilbert Cell"
The double-balanced multiplier/modulator/phase detector made from a tree of transistors with the collectors cross-coupled pre-dates the Gilbert Cell.

The Gilbert cell was a step further in using current mode signals and the I/V characteristics of diodes to make a fully linear four quadrant multiplier. He went on to develop it into log processors etc.

Full linearity of all three ports isn't usually needed in a mixer/phase detector/modulator, so the plain transistor tree (jones et al) is fine. The snag is that the plain tree seems to have acquired the Gilbert name in popular usage. But it isn't the Gilbert Cell, it's what the Gilbert Cell was developed from, so of course it came before.

There hasn't been any patents shenanigans, but we have some erroneous nomenclature now so deeply rooted that I'm not sure we'll ever get rid of it.

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Old 16th Dec 2019, 2:49 pm   #171
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Default Re: Repair nightmares.

Another 'gotcha' I came across was on a large 19-inch rack of data-acquisition gear in a Government research facility. All the data-acquisition modules had to be precisely synced to each-other so right in the centre of the rack was a trigger-pulse-generator/driver, from which thin coax cables - all of the same length, terminated with LEMO connectors - radiated.

One acquisition-module was sent back for service several times, each time 'no fault found'. On deeper investigation on-site we found that one of the trigger-distribution coaxes was about 18 inches shorter than all the rest. The shorter one showed signs of being 'bodged'. Turns out that one of the scientists had trapped a coax in between the rack-chassis and a data-acquisition module as he inserted the module. To cover up his negligence he'd had one of the techs cut the damaged bit off and fit a new LEMO.

That simple error put a major project back by about a month, costing the taxpayer a surprisingly-large amount.
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Old 16th Dec 2019, 3:35 pm   #172
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Default Re: Repair nightmares.

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Originally Posted by Welsh Anorak View Post
I was very pleased with the result, only to be brought in front of the manager who told me in no uncertain terms I should have refused to do anything as it was the production company's fault and could have reflected badly on us if it had gone wrong.
The number of times I've been on the carpet for going the extra mile...no good deed goes unpunished!
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Old 16th Dec 2019, 5:18 pm   #173
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Default Re: Repair nightmares.

As for dodgy components, Behringer had problems with faulty diodes in their NU6000 amplifiers, amplifiers were failing for no apparent reason and it turned out that certain diodes were failing for no apparent reason. Turns out they got sent a faulty batch of diodes from IR and had to recall the amps to have the diodes replaced.
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Old 16th Dec 2019, 5:33 pm   #174
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Default Re: Repair nightmares.

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Quote:
Originally Posted by Welsh Anorak View Post
I was very pleased with the result, only to be brought in front of the manager who told me in no uncertain terms I should have refused to do anything as it was the production company's fault and could have reflected badly on us if it had gone wrong.
The number of times I've been on the carpet for going the extra mile...no good deed goes unpunished!
In a similar vein I remember Chas Miller telling me how many years ago he had repaired a TV belonging to a local toff who lived in a big old manor house with a long drive. On returning the TV, said toff asked how much the repair was and Chas told him (it was a fair, reasonable price). At this the toff said, "Oh well, you couldn't have done a very good job otherwise you would have charged more than that". Chas was obviously trying to be fair and honourable and got chastised for it!
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Old 16th Dec 2019, 5:56 pm   #175
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Default Re: Repair nightmares.

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Chas Miller telling me how many years ago he had repaired a TV belonging to a local toff who lived in a big old manor house with a long drive. On returning the TV, said toff asked how much the repair was and Chas told him (it was a fair, reasonable price). At this the toff said, "Oh well, you couldn't have done a very good job otherwise you would have charged more than that". Chas was obviously trying to be fair and honourable and got chastised for it!
There's always a difference between the cost of something and the price you charge for it.

Cost is generally easy to determine; but as the above example shows, the price you should charge is intrinsically linked to the customer's expectations and preparedness/ability-to-pay - which can include such factors as "The big match is on in an hour - can you get it fixed by then?" and "this is the last of these in-service - we can't possibly replace it, we really hope you can fix it!!".

Desperation loosens the purse-strings!
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Old 16th Dec 2019, 6:06 pm   #176
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Default Re: Repair nightmares.

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As for dodgy components, Behringer had problems with faulty diodes in their NU6000 amplifiers, amplifiers were failing for no apparent reason and it turned out that certain diodes were failing for no apparent reason. Turns out they got sent a faulty batch of diodes from IR and had to recall the amps to have the diodes replaced.
My first boss told me of a similar issue. He was teaching in the Army School of Electronics (I think) and they had some students buid up circuits including electrolytic capacitors. Even though they had been warned to check and double check polarity, there was 'the sound of amps' and then a bang / shower of foil. After the third one did this he was beginning to think the students were winding him up and doing it deliberately but it turned out RS had delivered a batch of caps with the sleeve the wrong way round, spotted because with axials it's easy to see which lead is connected to the can.
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Old 16th Dec 2019, 6:09 pm   #177
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Default Re: Repair nightmares.

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Chas Miller telling me how many years ago he had repaired a TV belonging to a local toff who lived in a big old manor house with a long drive. On returning the TV, said toff asked how much the repair was and Chas told him (it was a fair, reasonable price). At this the toff said, "Oh well, you couldn't have done a very good job otherwise you would have charged more than that". Chas was obviously trying to be fair and honourable and got chastised for it!
There's always a difference between the cost of something and the price you charge for it.

Cost is generally easy to determine; but as the above example shows, the price you should charge is intrinsically linked to the customer's expectations and preparedness/ability-to-pay - which can include such factors as "The big match is on in an hour - can you get it fixed by then?" and "this is the last of these in-service - we can't possibly replace it, we really hope you can fix it!!".

Desperation loosens the purse-strings!
So true, but even then it can fall apart. What about if Chas had upped the price a bit to meet the expectations of the toff, then a few weeks later in a conversation at the local shoot, a beater tells him that Chas fixed his tele for a substantially lower price? Charging 'different prices' opens a massive can of worms. I provide a guitar setups service and I have standard prices and I stick to them. You just never know how information is going to get passed around. But I take your point and in the cases you mention 'varying' the price may well work.
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Old 16th Dec 2019, 7:16 pm   #178
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Default Re: Repair nightmares.

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I have spent my working life repairing electronics in hospitals. The repairs aren't the nightmare just where the equipment is. Think of intensive care units, A&E, maternity or baby care units. Dealing with non working kit next to a patient on a ventilator, or an ECG monitor attached to a pre-term baby.
When I retired I was repairing cancer treatment machines. More pressure to keep them working as they treat patients from 08:00 to 20:00 Monday through Friday and occasionally weekends.
If I made a mistake then patients could miss their treatment.

|Malcolm
Really surprised nobody else has commented on this post, or am I?..
Hats off to you Malcolm , makes all the other posts appear so unimportant.

Regards poppydog
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Old 16th Dec 2019, 8:22 pm   #179
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Default Re: Repair nightmares.

While I'm always happy to celebrate those keeping healthcare infrastructure alive, surely equal recognition should be given to those of us who supported the UK nuclear-infrastructure and helped keep the electricity on and our defences functioning 24x7x365?
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Old 16th Dec 2019, 8:39 pm   #180
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While I'm always happy to celebrate those keeping healthcare infrastructure alive, surely equal recognition should be given to those of us who supported the UK nuclear-infrastructure and helped keep the electricity on and our defences functioning 24x7x365?
Malcolms post touched a nerve as my granddaughter has just been born several weeks premature. I apologise if you feel offended by my post.
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