- TDA1085 - 1 Update
- Vintage equipment voltage measurement - 4 Updates
- Help for iPhone batteries on continuous charge? - 1 Update
| ggherold@gmail.com: Aug 20 07:57AM -0700 On Sunday, August 19, 2018 at 3:26:52 PM UTC-4, Baron wrote: > -- > Best Regards: > Baron. Octoparts? https://octopart.com/search?q=TDA1085C&start=0 George H. |
| Rob <nomail@example.com>: Aug 20 07:41AM >> that used by the people who wrote the service manual? > if too high add parallell resistance. > if too low select a higer voltage range. In the old analog meters, there basically was only a current meter, often 50uA full scale, and when measuring voltage a suitable series resistor is switched in to make it draw 50uA at the full scale reading. So a 10V range would have a total resistance of 10V/50uA = 200k (which would be the resistance of the meter itself plus the series R). At 10V measured voltage there is 50uA through the 200k resistance. When looking at this, any range will have a resistance of 1V/50uA per volt of range, hence "20K per volt". The 100V range will be 2M. This is no longer true for a modern DVM. They usually have a 10M series resistor on the input with selectable resistors to ground to make a voltage divider that outputs the desired voltage for the ADC. So, depending on the range you select, the input resistance will be 10M plus a small value that will get smaller when you select a higher range. Therefore there is no fixed "K per volt" input resistance anymore, and selecting a higher range will not result in a higher resistance. However, as already can be seen, the "20K per volt" is not really telling the input resistance to be used in the measurement. It depends on the selected range, and available ranges vary between meters. One may have ranges of 10-30-100 and another maybe 10-50-200. When you need to measure a 24V testpoint, on one meter it may be on the 30V range (and thus 600k resistance) and on another meter it would be the 50V range (and thus 1M resistance). It is expected that the person doing the measurement understands how this could affect the result, if it does at all. (when measuring a supply voltage, there should not be a noticable difference. when measuring in a high-impedance signal circuit, there could be) |
| Tom Gardner <spamjunk@blueyonder.co.uk>: Aug 20 09:27AM +0100 On 20/08/18 00:44, Jeff Liebermann wrote: > he does take a few measurements like the power supply voltages. > All this works very nicely as long as engineers don't try to act like > technicians and technicians don't try to act like engineers. There is, of course, one domain where that engineer/technician distinction is almost completely meaningless: software, particularly "enterprise" software. Worse, they are proud of it, and actively seek to merge all development phases. The end result is that many sticky fingers poke at the various parts of the system, and eventually nobody knows a system's specification or what it actually does. Provided it doesn't fail the tests, it is defined as working. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Aug 20 06:14AM -0700 OK - Let me start off with the statement, paraphrased from A.A. Milne: When you are a Bear of Very Little Brain, and you Think of Things, you find sometimes that a Thing which seemed very Thingish inside you is quite different when it gets out into the open and has other people looking at it. I have been repairing and restoring vintage equipment, as a hobby, for over 40 years now. For over 25 years of that time, I have used a Fluke auto-ranging DMM, and never a VTVM or similar vintage equivalent, although I have used same for comparative purposes. Discovering the following: a) Yes, I have gotten different voltage readings 'from the book'. b) Many (but not all) of which are explained by higher wall-plate voltages. c) The differences not explained by wall-plate voltages are usually consistent. d) Meaning that I can account for, and adjust to these differences without having to introduce outboard solutions. Peter Wieck Melrose Park, PA |
| John-Del <ohger1s@gmail.com>: Aug 20 07:21AM -0700 > d) Meaning that I can account for, and adjust to these differences without having to introduce outboard solutions. > Peter Wieck > Melrose Park, PA Just to add (and not referring directly to any measurements you may have made) that many discrepancies in measurements are the result of not following the service manual specifics regarding test conditions. A properly prepared SM will include the conditions of measurement - such as line voltage, warm up time, impedance of the meter, whether or not a signal is applied, setting of customer controls and service adjustments and placement of switches or functions selected. There are others I'm sure. |
| Mike Coon <gravity@mjcoon.plus.com>: Aug 20 09:14AM +0100 In article <e3a84aec-c1d0-40eb-8e1b-ae4702ec9a1c@googlegroups.com>, bruce2bowser@gmail.com says... > As many apps as possible should all be off when charging, too. That way, the phone is using less energy while charging. Please explain why that would make any difference... Mike. |
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