04-07-2015, 07:32 PM
Some wise words there. In summary, you have to be pragmatic. Which is easy with experience, but can be confusing at first. Especially if you have a nice new shiny DMM that is giving you figures like 2.9381V DC - we as humans like that sort of thing, even though it might be really quite a way off from reality (there is a massive difference between precision and accuracy).
Most well-designed circuits are very forgiving - from the ground up they would be designed to work well with the expected spread of component tolerances (and then some), plus the expected spread of supply voltage (and then some), plus the expected reception conditions. No experienced designer would sign off mass-production of anything that is super-critical or in any way fussy - that's commercial suicide. At the very least, detailed R&D would be needed to quantify the effects of the expected variations so that an informed decision can be made (and warning made in the service documentation). Far better and more economical to just design the circuit differently in most cases. Fortunately, negative feedback is extremely helpful in many situations like this
With most repair jobs, the voltage in question usually adopts one of two conditions: either "about right", or "miles off". The meter used shouldn't really be a big deal here, but of course, loading effects might be a concern in high-impedance areas.
When investigating more specialist equipment, or when doing circuit design, then yes, more detailed results are often needed. But by the time you're doing this sort of work, you'll have a much clearer idea in your own mind about what is going on, and will be able to account for any limitations in your gear (which, by this stage, you'll know intimately). But at this stage, try not to be put off by the "Volt Nuts" with their 7-digit multimeters (I have one, but rarely use it, and never for radio repair). A basic Uni-T or similar will do just fine. Rather than an analogue meter, I'd prefer to get an old-school analogue oscilloscope to supplement the DMM. My AVO 8s are sadly languishing in the attic - I feel rather guilty about that, but that's how it is...
Most well-designed circuits are very forgiving - from the ground up they would be designed to work well with the expected spread of component tolerances (and then some), plus the expected spread of supply voltage (and then some), plus the expected reception conditions. No experienced designer would sign off mass-production of anything that is super-critical or in any way fussy - that's commercial suicide. At the very least, detailed R&D would be needed to quantify the effects of the expected variations so that an informed decision can be made (and warning made in the service documentation). Far better and more economical to just design the circuit differently in most cases. Fortunately, negative feedback is extremely helpful in many situations like this
With most repair jobs, the voltage in question usually adopts one of two conditions: either "about right", or "miles off". The meter used shouldn't really be a big deal here, but of course, loading effects might be a concern in high-impedance areas.
When investigating more specialist equipment, or when doing circuit design, then yes, more detailed results are often needed. But by the time you're doing this sort of work, you'll have a much clearer idea in your own mind about what is going on, and will be able to account for any limitations in your gear (which, by this stage, you'll know intimately). But at this stage, try not to be put off by the "Volt Nuts" with their 7-digit multimeters (I have one, but rarely use it, and never for radio repair). A basic Uni-T or similar will do just fine. Rather than an analogue meter, I'd prefer to get an old-school analogue oscilloscope to supplement the DMM. My AVO 8s are sadly languishing in the attic - I feel rather guilty about that, but that's how it is...
