Hi there,
I'm a long time watcher of Dave's video's and find most of the things he shows and talks about to be informative, for some strange reason I also enjoy mailbag too. I have no reason to doubt his credentials and life experiences, actually I'm a fellow atheist so I like the guy for that reason alone!
I didn't want to join the forum to be a basher and I hope this first post is not taken the wrong way. Dave is very good at what he does in other areas but fault finding has me thinking most of the time "WTF is he doing......" and the latest Soniq TV repair video was the proverbial straw!
I don't want to make this a rant so will just cut to what I taught Electronics Technicians for some 30 odd years as a Workshop Manager and Trainer for Panasonic.
Do not deviate from these important steps -
1/ Confirm the customers description of the fault, also confirm the correct functionality of overall operation
2/ Check visually the outside for anything unusual or signs of damage, physical damage, liquid ingress etc
3/ Open the unit and recheck customers description of the fault, also reconfirm the correct functionality of overall operation
4/ Start a complete visual inspection looking for anything unusual, charring, over heating, damaged components, corrosion, obvious dry joints
Next -
- Always be aware of jumping to conclusions and following garden paths, don't go too deep too quickly. Reassess every now and then, why and what I am doing.
There are a number of branches the next steps could follow depending on the fault but basically in no particular order -
- Check for intermittents, tap test, flexing the PCB either by hand (safety first of course) or an insulated object.
- Alternating between a can of Freeze and a Hair dryer can help to isolate temperature related faults. Also helpful are small gas powered hot air blowers for pin point heating, even the hot tip of a soldering iron can be useful (be careful it is grounded)
- If you need to start tracing a fault then start with Power supply, Oscillators, Resets
- Don't assume ground is contiguous throughout the whole unit. I have seen many a technician fooled by an open circuit/floating ground while testing another PCB from a common ground point. Shift the ground point to the Circuit/PCB you are testing or check the ground continuity.
- Never assume that just because you have voltage you don't have excessive ripple.
- Before replacing a fuse (of any type) ask yourself "why did it fail?" check the resistance of the circuit on the secondary side.
- Carefully unplug, check and reconnect all relevant connectors
- Never change the design of a circuit or 'band-aid" components. You are not the designer and the circuit worked fine before it failed so fix it properly.
Always be aware of your personal safety, and the safety of the customer. Even if you are repairing your Mum's TV you don't want to kill her or burn the house down due to your shoddy repair - know your limitations and seek professional help if needed.
Of course there are things I have forgotten to mention.
My final point is, you can fault find with just a Multimeter. It is the most useful piece of test equipment you will have, try and get yourself an old type Analogue Multimeter too. An oscilloscope is also helpful, it doesn't have to be a storage one as I still use my analogue scope of 20 years. I know Dave uses some of the equipment he has for educational value but honestly you don't need them, they are just "bling" and can confuse rather than clarify a problem.
If you read this Dave, keep up the good work. I do admire what you are doing.
Back in the day,I was,among other things,responsible for the repair,& availability of Picture Monitors at a TV Studio.
This also included some top end Domestic TV sets.
Management decided to outsource the repair of some of the big Sony 27" Domestics,as they thought things were getting on top of us a bit!
We attached a note to the first set saying what we had checked,hoping it would be useful to the Serviceman.
After a couple of weeks we got a call that it was fixed.
When I picked it up,I noticed their job sheet attached to it.
Under "nature of fault",it said "doesn't work"!
So much for:-
"1/ Confirm the customers description of the fault, also confirm the correct functionality of overall operation"Ever"tigers for punishment",we sent another of these sets out to another Service company for a few problems.
We got a call:- "The tube is faulty!"
"OK",we said,& despatched a "regunned" tube to them,with strict instructions to return the old one intact so it could also be "regunned".
We got the tube back with the end knocked off,& the TV with the new tube "fitted",but not in any way converged,or any purity adjustments done.
We spent half a day finishing their job!
Luckily,the regunning place still managed to do the tube OK.
There was little talk about "outsourcing" from then on!
With the "in-house " stuff,when Production folk wanted a certain number of Monitors,you needed to supply them--or else!
There was not any case where you could write off a unit as "beyond economical repair",so we went to fairly extreme lengths to keep them available & meeting Broadcast specs.
Due to time constraints,we quite often had to bend the words if not the spirit of your injunction:-
"- Never change the design of a circuit or 'band-aid" components. You are not the designer and the circuit worked fine before it failed so fix it properly."
With some equipment,it didn't "work fine",so the same fault would recur-----for no other reason than the use of inadequate components in the original design.
Even with good designs,it was often necessary to fit different components because the original ones were unobtainable.
In every case,this led to a reliable & safe repair.