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bitrex <user@example.net>: Aug 11 03:41AM -0400 Problem with my Tekpower PSU:   <https://tekpower.us/downloadable/download/sample/sample_id/1/>   Here's a teardown on YouTube:   <https://youtu.be/Nfe28vGW6Ik>   Problem is it's developed a fault where the current meter always reads 0 when in constant-voltage mode. Everything else seems to work fine and it's putting out the right voltages, current limit works fine, when load current exceeds the set point it current limits OK and shows the correct value. Drop back and the display reads 0, again.   Here's the schematic (PDF), logic board only, unfortunately but the power board seems to be working OK.   <https://www.eevblog.com/forum/testgear/tekpower-tp3005t-variable-linear-dc-power-supply/?action=dlattach;attach=249613>   Overcurrent detection seems to work by voltages IS- and IS+ coming in from the off-board current shunt and sent to pin 19 of the PIC, which I believe is a comparator-interrupt pin, and that seems to work ok, and the voltages out of that op-amp and across the current shunt look OK.   Constant current mode seems to work by using TL082 section "N18BB" as a comparator open-loop, and then the loop is closed around back from the ADJ line that goes off-board to the power regulator board, and the current-set DAC output from the PIC, comparing the two inputs against each other.   Constant-voltage mode works similarly the voltage-set DAC value from the PIC is compared against the voltage at the output and a line is asserted when they match. The output voltage in CV mode looks OK.   It's not clear to me though how what the current actually is, in constant-voltage mode, is sensed by the PIC, as I don't immediately see a pin on it where the current-shunt voltage is being read by the uP, so it's hard for me to know where to look for the problem as nothing obvious is amiss, and continuity on all the connections between the boards to the PCBs seems OK.

bitrex <user@example.net>: Aug 11 03:54AM -0400 On 8/11/2020 3:41 AM, bitrex wrote: > it's hard for me to know where to look for the problem as nothing > obvious is amiss, and continuity on all the connections between the > boards to the PCBs seems OK.   Only other thing I notice is that the logic board ground and the PSU positive output seem to be connected, with the logic board fed by a separate isolated tap on the transformer. And it looks like one of the ADC inputs on the PIC is also connected to the logic board ground, so maybe some kind of differential ADC arrangement but how to diagnose still eludes me.

legg <legg@nospam.magma.ca>: Aug 11 08:36AM -0400 >> it's putting out the right voltages, current limit works fine, when load >> current exceeds the set point it current limits OK and shows the correct >> value. Drop back and the display reads 0, again. <snip>   Have you replaced the OP07?   Could be one output is unable to pull in one direction.   Or N18A . . .   Biasing to V13 doesn't look right, in the schematic, so you may have to deal with some typos there.   RL

bitrex <user@example.net>: Aug 11 12:12PM -0400 On 8/11/2020 8:36 AM, legg wrote:   > Biasing to V13 doesn't look right, in the schematic, so > you may have to deal with some typos there.   > RL   Yeah the diagnostic process is definitely not helped by the sloppy and confusing schematic. Before I jump into op-amp swapping I'm trying to understand how the current-sensing works in CV mode and is read by the processor so maybe I can trace it back, but I'm not very familiar with the PIC. Maybe it's reading the value from the "CCP" pin somehow that "VIS" connects to, pin 19, but the impression I got from the datasheet is those are some kind of comparator inputs for the over-current/over-voltage sensing, not ADCs. Not sure.   Like a lot of gear from China at this price point it's designed to meet a budget, but not badly designed to meet a budget and otherwise neatly constructed, but then often let down by some sketchy soldering on the connectors and through-hole parts. Often can "fix" this stuff by tapping the board to find the intermittent joint or just re-touching all the connectors but my first round of that didn't work, this time.

Jeff Liebermann <jeffl@cruzio.com>: Aug 10 11:32PM -0700 On Mon, 10 Aug 2020 22:33:34 -0700 (PDT), Jeff Urban   >So we got Fox's Mercantile who found offense. Is he a jew ?   List of Jewish last names. I'm on Page 18: <https://www.familyeducation.com/baby-names/browse-origin/surname/jewish?page=18> I couldn't find Jeff #2 last name on the list, so he must not be Jewish.   For what it's worth, I prefer very dry, deadpan, non-emotional humor. I've written some humor, but I don't think you will like it. <https://groups.google.com/forum/#!original/comp.unix.sco.misc/nYX8dJF3_Vo/_dCOorFX78wJ> <http://members.cruzio.com/~jeffl/nooze/nooze.htm> <http://members.cruzio.com/~jeffl/poetry/poetry.htm> No need to reply. I get tired of too much praise and adulation.     -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

"pfjw@aol.com" <peterwieck33@gmail.com>: Aug 11 05:03AM -0700 "I have dealt with the Fox's Mercantile type before. Born antagonists. This is the type of person who dares not go to certain bars because he might not make it out alive with his mouth. And he knows it and saves up all his energy for social media on the internet. He thinks being more of an asshole makes him right or proves his point. Of course neither is true."   Having met Mr. Angus at his home base of Ranger, TX, I can guarantee you that there is no bar on the planet that would refuse his custom, nor where he would be at any risk whatsoever. He is just as opinionated in person as he is in this venue. You, on the other hand, impress me as being a professional chameleon, with no 'true colors'. Yes, that is an insult.   Peter Wieck Melrose Park, PA

Fox's Mercantile <jdangus@att.net>: Aug 11 10:18AM -0500 > You, on the other hand, impress me as being a professional > chameleon, with no 'true colors'. Yes, that is an insult.   And, as expected reacted exactly as predicted.   First off though, I'd have to value his opinion before he could insult me.       -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com

John-Del <ohger1s@gmail.com>: Aug 11 08:56AM -0700 On Monday, August 10, 2020 at 5:59:14 PM UTC-4, Jeff Liebermann wrote: After > works. We just buy everything in sight. At this time, we own > Hollywood, banking, music industry, garment business, congressional > lobbyists, and have a monopoly on Nobel Prizes.   I don't mind that at all, but I've always been a bit resentful that my Jewish friends not only cut me out of the plan, but categorically deny all of this.   Now that I've got a Jewish daughter-in-law, I'm more aggravated being on the outside looking in. She says it's turnabout because I've never cut her in to the Mafia riches we EyeTalians enjoy.   Touche I guess..

Adrian Caspersz <email@here.invalid>: Aug 11 09:26AM +0100 > Much as a Ducati or a Triumph or a BMW is a special sort of Scooter.   https://en.wikipedia.org/wiki/Contactor   -- Adrian C

Jeff Liebermann <jeffl@cruzio.com>: Aug 10 11:11PM -0700 On Tue, 11 Aug 2020 04:45:31 -0000 (UTC), bob prohaska >So, I can walk into a facility posted "no cellphones or cameras" >carrying a turned-off cellphone with a camera plus bluetooth and >not be found out so long as I don't turn it on? Most surprising!   Yep. Better yet, you can have the phone power turned ON, and put the phone in "airplane mode", and not be found. Airplane mode turns off cellular, Wi-Fi, BlueGoof, and possibly NFC. The idea is to prevent any emissions (transmissions) coming from your phone from affected the airplane navigation and communications equipment and causing problems with overloading the local cell towers. Think about 250+ passengers checking into one cell tower upon landing: <http://kwc.org/mythbusters/2006/04/episode_49_cellphones_on_plane.html>   However, there's a catch. Even if airplane mode is turned on, you can turn Wi-Fi and BlueGoof back on. The only part that must be turned off in airplane mode is cellular. Worse, some apps can turn on Wi-Fi or BT when invoked. For example, I recall a BT walkie talkie app that managed to enable BT on startup while in airplane mode. That was years ago, and was presumably fixed by now.   There are also apps that want internet access and provide a helpful dialog box asking the users if they want to connect. It's easy enough to do that by mistake. Yep, I just tried it. I turned on airplane mode, which correctly disabled cellular, Wi-Fi, and BT. I started Firefox browser, which immediately complained "Server not found" and offered me the choices of "Enable Wi-Fi" or "Try Again". However, when I clicked "Enable Wi-Fi", it spun merrily for about 5 minutes, but didn't turn on the Wi-Fi. So, I have a phone[1] where one function is trying to turn OFF Wi-Fi, while another is trying to keep it turned OFF. Toss a coin? Chrome browser did it right by simply announcing "No Internet" and only offering "Cancel" as a choice. Edge browser also did it right by providing some useful suggestions and offered only "Download when online".   Bottom line is you're probably safe in "airplane mode" but need to be very careful not to be tricked into turning on Wi-Fi or BT, or having some application do it for you.   >Thanks for writing, >bob prohaska   [1] Google Pixel 1 running Android 10.   -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

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