hybridfree/eevblog-posts huggingface dataset:
How does this pre-TTL keyboard circuit work? - Page 1
Forum section: electronics / repair

author: rea5245
author_rank: Frequent Contributor
timestamp: December 23, 2023, 04:23:28 pm
content: Hi. I've attached a schematic for a Wang 360 calculator keyboard from the 1960s. I want to decode button presses from it. It uses logic driven by -11V, 0V, and +11V. My knowledge doesn't go very far beyond digital TTL circuits, so my head's spinning trying to understand this.When the micro switches are open, what's the voltage on the KBn lines? I'm guessing 0V. At point A in the schematic, they're tied to a IN754 zener, which is then connected to 0V. Should I assume all the switch columns are similar, and they just didn't bother drawing it?But at point B, micro switches are tied to 0V differently, through a resistor and diode. Why the difference?When a micro switch is closed, the KBn outputs go to the voltage at point C, which looks like it would normally be 0V. So that means the KBn lines are 0V whether the switches are open or closed.I'm wondering if the switch is changing the impedence, and the host device is supposed to have a pull-up to +11V or pull-down to -11V on the KBn lines.Meanwhile an input from KBC can turn on the 2N404 transistor and again pull point C to 0V. It looks like point C is 0V no matter what. I must be missing something. What could the function of KBC be?Then there's the KBD signal. I think it's an output to the host device, and it's the same voltage that will come out the SWn lines when those toggle switches are off. I think it's going to be -11V - unless KBC is active, in which case KBD will go to 0V. But what's the point of having KBD go to the host device? And why drive the toggle switches from point E while all the micro switches are driven from point C?There's a KBE signal. I assume that's an output to the host that indicates how the keyboard's On/Off switch is set. When the switch is off, KBE is 0V. When the switch is on, it's -11V.I'd appreciate any help.Thank you.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 23, 2023, 05:41:59 pm
content: Let's start with you posting the schematic. Attachments can act funny here, so always check after you post.RDL logic came before TTL. That's one possibility.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 23, 2023, 06:03:39 pm
content: This section (attached) looks a bit like what's described here:https://en.wikipedia.org/wiki/Diode_logic#:~:text=An%20active%2Dlow%20OR%20diode,ground%2C%20the%20output%20goes%20low.Besides using such old equipment, I never got into studying it during that era. Hope that link helps.
How hard to replace Tek scope probe cable - Page 1
Forum section: electronics / repair

author: jdutky
author_rank: Regular Contributor
timestamp: October 02, 2020, 02:24:39 am
content: I have a Tek 475 scope with two original probes (P6075A) one of which appears to have a fault in the middle of the cable. I am wondering how difficult it would be to replace the cable, assuming that I can obtain the replacement part (which I have seen for sale on-line for quite reasonable prices). I know that the center conductor is a single hair-thin wire, and that I might need special tools just to properly strip the fine coax, and that's daunting enough, but is there more to the job than just very, very delicate surgery and soldering work?Thanks for any help.

author: tggzzz
author_rank: Super Contributor
timestamp: October 02, 2020, 08:56:06 am
content: Quote from: jdutky on October 02, 2020, 02:24:39 amI suggest you search the TekScopes archives; there is a lot of useful info there.

author: Gyro
author_rank: Super Contributor
timestamp: October 02, 2020, 12:49:22 pm
content: Not hard, it's all documented in the P6075A Manual...https://w140.com/tekwiki/wiki/P6075

author: chris_leyson
author_rank: Super Contributor
timestamp: October 02, 2020, 01:21:02 pm
content: i don't think it's standard 50 75 Ohm coax. Sorry didn't read the ops post, replacement is not too difficult on the older probes.

author: tggzzz
author_rank: Super Contributor
timestamp: October 02, 2020, 01:37:05 pm
content: Quote from: chris_leyson on October 02, 2020, 01:21:02 pmCorrect; it is averylossy cable to minimise (internal) reflections.

author: Gyro
author_rank: Super Contributor
timestamp: October 02, 2020, 03:21:59 pm
content: The OP said he had seen the replacement part for sale on line for quite reasonable prices. So that's hopeful.
How long is Dyson V8 battery life? My Machine broken? - Page 1
Forum section: electronics / repair

author: Annava
author_rank: Newbie
timestamp: December 30, 2022, 08:57:30 am
content: Battery indicator light show green, used for 1 year. Found that there are 2 years battery life in generally.

author: abdulbadii
author_rank: Frequent Contributor
timestamp: December 30, 2022, 11:08:53 am
content: if possible, open it up completely to be able to read each cell's voltageif below 2.7V it's faulty, check BIR, battery internal resistance if greater than 0.7 it's faultyLi-ion damage mostly caused by two- charged full but not being used quickly then- affected by high temperature, readhttps://www.plarad.de/fileadmin/downloads/FAQ_related%20to%20lithium%20ion%20rechargeable%20battery%20care_DA1_en_0216.pdf

author: MunsterAbu
author_rank: Newbie
timestamp: December 30, 2022, 02:37:31 pm
content: Apologies if this is way off base but are you cleaning the filters regularly? I replaced a battery before realising that dirty filters absolutely kill the battery life.

author: YurkshireLad
author_rank: Frequent Contributor
timestamp: December 30, 2022, 03:00:41 pm
content: One of our Dysons powers off if the filter is too dirty. Maybe check the filter.
How multimeter detects that it is in the current measurement mode? - Page 1
Forum section: electronics / repair

author: trenchsoldering
author_rank: Newbie
timestamp: February 22, 2022, 09:53:55 pm
content: Hi,I toasted a little bit my multi-meter Aneng Q1.I wanted to measure voltage, but my gadget was in current measuring mode (10A).I short circuited 3A 48v charger.I didn't notice the issue right away, because it didn't broke completely.It stuck in current mode. It reacts on buttons, but I cannot choose voltage mode, because current/voltage is guided bywhich port has write in.So I have a hope that fix is not hard and I am fix it myself, but I don't have enough information about method for detecting where wire is plugged in.What elements on PCB should I check first in this case?Thanks

author: inse
author_rank: Super Contributor
timestamp: February 22, 2022, 10:16:54 pm
content: Fuse!

author: mikerj
author_rank: Super Contributor
timestamp: February 22, 2022, 10:31:40 pm
content: Multimeters that sense the probes being connected usually have split contacts in the 4mm sockets instead of a single contact. Inserting the probe connector shorts the two contacts together.Presumably your 3A charger was not current limited and has blown the 10A fuse.

author: strawberry
author_rank: Super Contributor
timestamp: February 22, 2022, 11:33:39 pm
content: when lights turn off

author: abdulbadii
author_rank: Frequent Contributor
timestamp: February 23, 2022, 12:36:17 am
content: Obtain MM else, open Aneng MM up at rotary switch to find continuity of V, I after replacing fusecheck others short connections

author: tooki
author_rank: Super Contributor
timestamp: February 26, 2022, 10:38:31 am
content: Quote from: abdulbadii on February 23, 2022, 12:36:17 amThat model doesn’t have a rotary switch.

author: relax
author_rank: Newbie
timestamp: April 21, 2022, 04:41:28 pm
content: I've had the same issue.Check the two N-Channel Mosfets "A6SHB" (SI2306) at Q4 and Q5. I've replaced both and it works again.
How on dual wattage soldering iron - Page 1
Forum section: electronics / repair

author: abdulbadii
author_rank: Frequent Contributor
timestamp: February 20, 2023, 11:25:20 pm
content: How's actually working mechanism of dual wattage soldering iron what's the extra wire, so total 3 wires, connected to the heated iron ?

author: themadhippy
author_rank: Super Contributor
timestamp: February 20, 2023, 11:53:14 pm
content: element 1 ,element 2 ,common for both elements?
How Renew Components Cleaned Tin ??? - Page 1
Forum section: electronics / repair

author: Alx
author_rank: Newbie
timestamp: October 19, 2021, 07:22:25 pm
content: Have you ever noticed electronicRenewcomponents such as ICs and transistors?The Pin IC and transistors tin is completely cleaned.It looks like it has never been soldered before.my question is. How is this done? Is there a specific solvent?

author: ataradov
author_rank: Super Contributor
timestamp: October 19, 2021, 08:04:16 pm
content: Yes, this happens a lot, especially to power transistors. Sometimes you even see legs that are extended and it is not very noticeable without examination.Given that stock ICs are coated, there must be industrial machines for that. In a less industrial environments, I've seen people dip the IC into a solder bath and use air gun to blow away the excess. But this is only viable if labor is virtually free and components are expensive.

author: abdulbadii
author_rank: Frequent Contributor
timestamp: October 19, 2021, 10:41:44 pm
content: On its standalone, (some of) its pins heated to molten the minute tin remnant and immediately wiped/applied with near-strong acid damped clothe and brush with very fine metal brush or sandpaper and immediately cleaned/wiped out with IPA damped clothe
How to (not) access the HV assy. in a TDS694C. - Page 1
Forum section: electronics / repair

author: Jwalling
author_rank: Unknown
timestamp: June 05, 2020, 03:38:47 pm
content: This Tek TDS694C scope was sent to me by a customer for repair of the HV assembly.This is exactly why the label on the rear states "No user serviceable components inside..."There was more, but I didn't take pictures.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 05, 2020, 03:43:04 pm
content: Quickest way of removing one's stash of bank notes from a DSO before sending it for repair.You're lucky if he didn't use the can opener on the CRT...

author: MadTux
author_rank: Frequent Contributor
timestamp: June 06, 2020, 10:26:34 am
content: Well, Tek failed to keep the user out of it...... ;-D

author: eKretz
author_rank: Frequent Contributor
timestamp: June 06, 2020, 04:32:23 pm
content: Oh noes. Tell me that the culprit wasn't the guy who sent it to you at least...

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: June 06, 2020, 08:08:12 pm
content: Quote from: Jwalling on June 05, 2020, 03:38:47 pmEvery engineer on the planet: "Hold my beer".

author: Jwalling
author_rank: Unknown
timestamp: June 07, 2020, 09:17:25 am
content: Quote from: eKretz on June 06, 2020, 04:32:23 pmYes, he was. He did apologize...

author: Jwalling
author_rank: Unknown
timestamp: June 07, 2020, 09:19:42 am
content: Quote from: BreakingOhmsLaw on June 06, 2020, 08:08:12 pmRTFM? Fuck that!

author: charlyd
author_rank: Frequent Contributor
timestamp: December 10, 2020, 12:12:45 pm
content: why in the hellwould somebody do that... maybe he was angryindeed Jay keep them out....

author: eKretz
author_rank: Frequent Contributor
timestamp: December 11, 2020, 05:02:10 am
content: Oh my. That is one determined ham-fist.
How to access internals of Seiki smart speaker - Page 1
Forum section: electronics / repair

author: rbm
author_rank: Regular Contributor
timestamp: September 18, 2022, 09:05:10 pm
content: Friend of mine has an obscure portable smart speaker branded as Seiki. The internal battery has reached end of life and won't hold a charge very long so he wants to replace it if possible. There is no obvious way to get at the internals. The speaker is covered in what looks like a rubber material to make it water resistant and there are no access panels to remove. There's also no information online about this speaker so no parts diagrams or user manual.How is it possible to get access to the battery?

author: electr_peter
author_rank: Unknown
timestamp: September 18, 2022, 09:43:24 pm
content: I don't know about this specific model, but most wireless speakers are not designed for easy disassembly and battery replacement, as some parts are glued together. Especially "water-proof" ones.However, repair is still possible, as internals are very simple. I would start by carefully removing grills from speakers - there could be some screws under them holding speakers. With speakers removed you have access to PCB.

author: richnormand
author_rank: Unknown
timestamp: September 18, 2022, 10:44:47 pm
content: Any hope of a friendly dentist or vet that could do an xray of suspect area (under control membrane or near speaker grill) for holders or hidden screws?Friend of mine saved my butt several time taking apart small stuff like a computer mouse avoiding undue damage.

author: fzabkar
author_rank: Super Contributor
timestamp: September 19, 2022, 12:01:42 am
content: Is there an FCC ID on the unit? If so, the FCC web site may have internal photos.
How to Adjust the AD834 Circuit - Page 1
Forum section: electronics / repair

author: daisizhou
author_rank: Super Contributor
timestamp: February 03, 2022, 05:44:37 am
content: The circuit schematic is as follows.I use a 500KHZ sine wave signal generator as the signal source.Tested the TP4 TP5 TP6 voltage value according to the DBM value and VRMS value corresponding to the 50 ohm load.TP5 voltage is equal to TP4 voltage amplified by 10 times.TP6 voltage is equal to TP4 voltage amplified by 100 times.Look at the data TP5 TP6 data At the end (where the red circle is drawn) the voltage amplification has entered the cut-off area.How do I adjust it to be correct?If you know please let me know, thanks for your help

author: dzseki
author_rank: Frequent Contributor
timestamp: February 03, 2022, 06:47:49 am
content: Is this circuit your design?A couple of points I see:-Why do you have three opamp stages cascaded on the output, while you you could do that in one shot.-Are you sure the AD834 is treated well? The power supply feed resistors are not equal 160R vs. 10R while due to the differential nature of the IC the quiescent current is roughly the same (the bias current on the output to be exact, which makes most of the quiescent current).-The RC network (100R + 100nF) on the output of the AD834 will make a corner frequency of about 16kHz.-Also the AD834 has "open collector" output, so connecting a cap directly to the output is also not a very good idea.

author: daisizhou
author_rank: Super Contributor
timestamp: February 03, 2022, 07:56:43 am
content: -This circuit is not designed by me, I am debugging this circuit.-Because TP4 (S3), TP5 (S2), TP6 (S1) are connected to the analog switch chip, and finally connected to the AD chip, and then processed by the single-chip microcomputer, the output is cascaded with three operational amplifiers-I didn't change the circuit, I checked the actual picture, the only difference is that the R33 (47K) resistor was removed, and the R29 (47K resistor value was replaced with 22K)Because when I input 2dbm (0.282mv), TP6 has reached 6.006V, and then high, TP6 has not changed.I want to get the correct change

author: dzseki
author_rank: Frequent Contributor
timestamp: February 03, 2022, 08:19:58 am
content: Ok, look at this:AN-212There is your circuit right on figure 3! I'm sure with the help of the circuit description you should be able to figure out what's the problem.

author: daisizhou
author_rank: Super Contributor
timestamp: February 03, 2022, 11:31:18 am
content: Thanks for your reply, I need to translate it to try to understand due to language differences, but it's hard.I tried adding two 200nf capacitors at C50 and C51 and found that the minimum voltage of TP2-TP3 decreased further, the minimum reached 0.17mv, the TP6 test point seemed to improve, but as I further increased the capacitor value at C50 and C51 , the TP2-TP3 voltage difference becomes larger againI don't know which modification is correct
How to avoid damage when trying to reflow this laptop graphics chip - Page 1
Forum section: electronics / repair

author: Kahenraz
author_rank: Contributor
timestamp: September 30, 2020, 07:08:22 am
content: I am trying to revive an IBM ThinkPad T41. The laptop boots but there are lines and pixel snow on the display when powered on. I am confident that the screen itself is fine. From my research, this laptop is known to have an issue with the video card failing due to cracked solder joints.I have already ordered a replacement motherboard so this is just an exercise for experimentation.The GPU uses an older style package that is not modern flip-chip. The memory is also adjacent to the GPU. It was released around 2001 so I don't think it uses ROHS solder.I am planning to reheat the board from below and then apply heat from above with a hot air station after doing my very best to get some no-clean flux under the chip by dripping it in from the side.Given the age of this board, what are temperatures are recommended for reheating and for reflowing the solder? I want to try and avoid damaging the board further.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 30, 2020, 10:20:11 am
content: Normally you would reflow the chip by hot air, but in some cases, like the nvidia video card chips who had theses problems ....The best method i think would be to protect all the surrounding component from excessive heat by a kapton tape, or you coud use some peel off foam, you apply it on all the surrounding parts, let it dry, and you could put a tape over the parts, you need to keep the parts from moving when heating ... the air flow could be strong ... the white connector can melt ??And you remove the video processor chip ... not sure the 2x memory chips will move too ?? and you reball the pga pins on the pcb and reball the video processor ... and put them back together ...You have many videos on youtube

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 30, 2020, 12:40:02 pm
content: hi,I resoldered thousands video chips on a metcal machine, never had a T41/T60 ...just press the video chip with your thumb really hard and start the pcI really doubt it's the video chip this time

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 30, 2020, 12:45:29 pm
content: for reflow look herehttps://www.okinternational.com/File%20Library/Metcal/Resources/White%20Papers/Metcal-Profiling-for-successful-BGACSP-Rework-White-Paper.pdfBUT imho look for lcd cable problems and lcd itselfthe vga output looks ok? if vga chip starts to develop bad soldering, sometimes vga out also becomes problematicdon't forgot, thumb test never failsif you resolder, prepare a good flux alsopersonally, I had best results with 220-240 degrees C on top side (chip side) and 180-200 bottom side, but I had that 26k$ reflowing machine, if you use a 100$ bga reflowing station, it's dead in the woods

author: Kahenraz
author_rank: Contributor
timestamp: October 01, 2020, 10:35:43 am
content: I've always had very little success with kapton tape (the air just blows around and underneath it).What's this about peel off foam?
How to break pump assembly off of motor - Page 1
Forum section: electronics / repair

author: electromateria
author_rank: Regular Contributor
timestamp: July 12, 2021, 05:01:00 am
content: Do I just pry it apart with force? All visible bolts are removed, etc.

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 12, 2021, 05:16:14 am
content: I'd try a hammer, work both sides.

author: james_s
author_rank: Super Contributor
timestamp: July 12, 2021, 05:40:37 am
content: Tap the volute with a rubber mallet and it should pop off. The impeller will usually be threaded onto the shaft, usually I end up having to break it to get it apart. It's a good idea to source replacement parts before you take it completely apart.

author: electromateria
author_rank: Regular Contributor
timestamp: July 12, 2021, 08:51:58 pm
content: @james_s - yea I had the same issue, had to break it to pop it off. doesn't seem like it's well designed with repair and maintenance in mind. the motor isn't damaged at least

author: james_s
author_rank: Super Contributor
timestamp: July 12, 2021, 08:53:38 pm
content: It would be nice if the shaft was stainless but they usually aren't. I had to turn a stainless sleeve for the shafts on both of the pumps in my hot tub, fortunately the replacement impellers were readily available so it wasn't too hard to rebuild them.
How to chose between iIntel P8255A variations - Page 1
Forum section: electronics / repair

author: gkmaia
author_rank: Frequent Contributor
timestamp: April 10, 2020, 06:32:07 am
content: Hi, i got a piece of gear that needs a new Intel P8255A.The intel datasheet is very vague when it comes to the variations.Most what I find for sale describe P8255A, P8255A-2, P8255A-5 as all the same. I imagine the difference between them may be max frequency?Not sure if that is of any help but my CPU is running at 6Mhz.

author: greenpossum
author_rank: Frequent Contributor
timestamp: April 10, 2020, 07:00:06 am
content: If you look at the datasheet from the Internet that describes the 8255A and 8255A-5 there are minor differences in the requirements for signals. I haven't found a datasheet describing the 8255A-2 yet.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 10, 2020, 12:23:52 pm
content: you have the high performance cmos version 82c55a ?? it's pin compatible with the 8255
How to clean an SMA gage kit - Page 1
Forum section: electronics / repair

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 10, 2023, 07:43:14 pm
content: I recently received a Maury A027A SMA gage kit. Unfortunately, the gage mating surfaces did not have protective caps over them and the foam apparently degraded, leaving residue on the mating surfaces. The foam was replaced when I received it, but the residue is still there. I would expect the foam material is polyurethane, which is a common choice for these sorts of things and degrades over time. However, I can't be sure.Any recommendations as to how to clean this? I've attached an image showing the mating surface of one gage. This is one of the worst ones, but the rest are similar. Normally, I'd use a fine-tip q-tip with some IPA. But, I'm not sure that's small enough and I'm also not sure it will remove residue that's probably gotten into the space between the sliding mechanisms. I've also thought about standing it upright (mating surface down) and soaking the end in some sort of solvent. I could try IPA, though it may not be effective enough. Another option is naphtha, which I believe should be effective on the residue and safe on the metal surfaces. I wouldn't want that to get residue further up into the sliding mechanism. Or, having the naphtha remain in those tight spaces. Are those risks? Thoughts on this solution? Other thoughts?I tried blowing it out with an air compressor, but the substance is too sticky and won't budge.If it's not easy to clean, I can return this for a refund. But, if I mess it up, I'll lose that right. So, I'd prefer not to try anything that is unlikely to work or could cause damage.

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 12, 2023, 04:17:52 am
content: I saw this post, which seems to corroborate my concern about something like naphtha spreading the goo further into the gages:https://www.eevblog.com/forum/projects/hp-probe-boxes-foam-melt-corode-nasty-solution-anyone/msg5141694/#msg5141694.The seller recommended warm, soapy water and a q-tip, but I don't think a q-tip will get in there and if I soak it, I'd be worried about the water getting trapped between the gage cylinders and causing corrosion. In fact, I'd be worried about any sort of liquid getting stuck there.Anyway, I just decided to return it.

author: Swake
author_rank: Frequent Contributor
timestamp: December 12, 2023, 06:59:29 am
content: It is a mechanical device. You can probably dismantle the front part from the dial. These kind of dials are used in mechanical shops with all sorts of attachments.As a 'stick' you can use dry wood. Easy to cut at any dimension. Think toothpick with a thin piece of cloth.Avoid using anything metallic, you will scratch the surfacesAny chemical needs time to act, some are quick some are slower. When you apply IPA give it a minute. Apply more if it dries up and you're not done cleaning. Use a squeeze bottle with fine nozzle with IPA to rinse the residue.Distilled water kan help rinsing and is very cheap so you can apply it in big quantities. Rinse the water with IPA
How to clean edge connectors (old HP silver colored ones) - Page 1
Forum section: electronics / repair

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: September 20, 2023, 06:55:37 pm
content: Hi,I have some older HP cards that have the shiny silver plating on the edge connections . Several show very poor continuity.I've tried cleaning with an eraser and then some De-oxit and they are much better but wondering if a scrub with some soft scrub would help.Any suggestions.Cheers,Corby

author: alligatorblues
author_rank: Regular Contributor
timestamp: September 21, 2023, 01:35:00 am
content: I use 600 grit silicon carbide paper, dry. Just enough to shine 'em up a bit.

author: coppercone2
author_rank: Super Contributor
timestamp: September 21, 2023, 01:40:41 am
content: you can dust it with a rubberized abrasive ultra fine cup wheel

author: edpalmer42
author_rank: Super Contributor
timestamp: September 21, 2023, 02:51:45 am
content: Perhaps one of those Magic Erasers would work. It's actually a very fine abrasive made of Melamine foam.Don't forget to check the socket in case one or more contacts is bent or has lost its spring tension.Ed

author: themadhippy
author_rank: Super Contributor
timestamp: September 21, 2023, 02:56:35 am
content: the ole way was to use a bit of silver paper from your fag packet

author: coppercone2
author_rank: Super Contributor
timestamp: September 21, 2023, 01:12:10 pm
content: Quote from: themadhippy on September 21, 2023, 02:56:35 amelectrochemical polishingsomeone should sell the stuff on a roll with a peel so you can have it around as a shop item
How to connect this relay pin definition - Page 1
Forum section: electronics / repair

author: daisizhou
author_rank: Super Contributor
timestamp: February 06, 2022, 11:55:42 am
content: The schematic diagram of the circuit is as follows.K12 and K13 can be closed or opened individually.On the right is the physical definition diagram.I don't know how to connect the pins for 10DB and 20DB functionality.This is a high voltage decay sampling circuit.If you know how to connect please let me know, thanks for your help

author: ledtester
author_rank: Super Contributor
timestamp: February 06, 2022, 12:34:43 pm
content: Based on this:http://www.learningaboutelectronics.com/Articles/DPDT-relay-wiring-diagramI would say 4/13 is the common pair, 6/11 is the NC pair (connected to COM when unenergized), and 8/9 is the NO pair (disconnected from COM when unenergized).As for the schematic, this is how I guess it works:

author: wn1fju
author_rank: Frequent Contributor
timestamp: February 06, 2022, 12:57:04 pm
content: You should look carefully at any notes accompanying the schematic. Does the schematic show the circuit with the relays energized or un-energized? Depending on that, the pin assignments given above might be reversed (6-8 and 9-11).Also, in some rare cases, the relay coil (1-16) might be polarized, that is to say, the +12V may need to go specifically to one side of the coil.If you are working on an existing piece, try to get the model number of the relay and look for a specification sheet.
How to disable DVD mechanism? (DVD Player) - Page 1
Forum section: electronics / repair

author: dougduck
author_rank: Newbie
timestamp: June 30, 2024, 09:36:46 pm
content: I have a DVD player whose mechanism is damaged, i wanted to deactivate it but when i disconnect the cable ([tr in][tr out][LOAD+][LOAD-]) the device does not stay in standby, it turns on by itself to try to detect the disk.Does anyone know if it's possible to disable it?

author: jzx
author_rank: Regular Contributor
timestamp: July 01, 2024, 05:02:32 pm
content: Perhaps it is triying to close the tray, but disconnecting the cable you have disconnected the switch that detects the position of the tray.What is the original problem with the mechanism?Often the belts have degenerated with time, slip, and the mechanism cannot reach the correct position, so the microcontroller try for long time until it gives up.You can try cleaning the belts, and try to aid the mechanism when it is closing, to see if it reaches the correct position.Another trick, if the belts are too rigid, is to boil them some minutes, sometimes this soften the rubber and the belts grip better, is not a good solution, the good one is to change the belts, but tuis trick can serve you to see if they are the problem.

author: dougduck
author_rank: Newbie
timestamp: July 01, 2024, 11:43:45 pm
content: Quote from: jzx on July 01, 2024, 05:02:32 pmExactly. The device restarts to try to close the tray.I solved the problem by grounding the TR OUT pin.thanks!!
How to disassemble an Amphenol 703-91T-3475-001 plug - Page 1
Forum section: electronics / repair

author: loop123
author_rank: Frequent Contributor
timestamp: March 04, 2024, 02:47:12 am
content: I've been googling for 2 hours how to disassemble this 7-pin Amphenol 703-91T-3475-001 adaptor but couldn't find any video at youtube nor any instructions at the manufacturer site.How to disassemble an intact one? I need to disconnect the -7.2V and +7.2 inside the plug. I don't need the dc, the other end is just cut open ended.I have a separate question. If I don't remove the dc, and the cable (see the cable spec above) wires are connected to live 7.2V DC all the time with the other end open ended. Can it somehow cause interference in the other signals inside the wire? If not, if the DC is sine wave, can it cause interference (form standing wave) with open ended wire (for future reference)? Thanks.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 04, 2024, 03:31:05 am
content: DC is not a sine wave and should not cause interference with the signals. I would suggest using a DVM set to AC volts and checking those two wires at the open end of the cable and see if you can measure any AC volts on them. You should not find any AC voltage, only DC (possibly, if it's being back feed from your device).From the pictures, it looks like you can slide the black jacket (upper left in picture) off of the connector and then slide the outer shell (right of center) off and back onto the cable and then lift the smaller half of the main body (left center in picture) off and then remove the two screws and the clamp and lift out the cable while slipping the connector and pins out (on the far left) of the other half of the shell (top right part). The black outer jacket and the strain relief (black part lower right) and the other shell should remain on the cable.That black outer jacket may be pressed on and may be hard to remove.

author: LuisBe
author_rank: Newbie
timestamp: March 05, 2024, 02:17:12 pm
content: Hello and greetings. I have uploaded a video disassembling a connector similar to the one you have, thanks to the indications of a co-worker (thanks Raul D.). I hope it will help you.Greetingshttps://youtube.com/shorts/AFnM7lr0xzc

author: tooki
author_rank: Super Contributor
timestamp: March 05, 2024, 07:46:05 pm
content: LuisBe shows the basic idea in the video, but I suggest using a mounted mating jack (or Amphenol’s special tool) to hold the insert rather than pliers, which can leave marks. The two flat areas on the plastic backshell are for a wrench, which may be necessary if it’s quite tight (or if you don’t have good finger strength).
How to dismantle this dashcam? - Page 1
Forum section: electronics / repair

author: meanie2
author_rank: Contributor
timestamp: September 16, 2021, 01:52:00 pm
content: Hi! Anyone disassemble one before?I'd like to remove the lens properly, manufacturer refuse to teach.There's no screw on the casing...sjcam.com/product/sjdash/More angles of the dashcam:jwtechreviews.com/2017/08/08/sjcam-sjdash-m30-dashcam/Please help. Thanks.

author: xrunner
author_rank: Super Contributor
timestamp: September 16, 2021, 03:13:07 pm
content: Quote from: meanie2 on September 16, 2021, 01:52:00 pmYep, I have lots of items like that. Although I don't have the item you are trying to disassemble, I would bet that it's snapped together. You need a spudger tool -https://en.wikipedia.org/wiki/SpudgerIf you want to risk damage (because you have never taken one apart), you can try pushing and prying the case apart where it looks like there is a seam where two parts snap together. No guarantees of course.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 16, 2021, 11:43:24 pm
content: I don't know but I'd guess adhesive, like a phone.

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 17, 2021, 08:34:09 am
content: those toolkits from ifixit works wonders for dismantling those pamperseven if i had a r&d electronics lab, i buyed one for smartphone battery personal jobs, proves useful for that new era of one-use designed hardwareif you don't like their prices, buy different ones, but that's the ones i use and recommend ( i got his onehttps://www.ifixit.com/Store/Tools/Pro-Tech-Toolkit/IF145-3073 years ago)

author: meanie2
author_rank: Contributor
timestamp: March 13, 2022, 04:19:51 pm
content: There's a bit of 'play' on the 'barrel' surrounding the lens.Trying my luck again to see if anyone knows.

author: kinswad
author_rank: Newbie
timestamp: March 13, 2022, 08:57:29 pm
content: Might not be 'snap together' OR 'glued' but ... sonic welded. In which case, might be a 'dremel' to get it apart?
How to drop 14V AC to 12V AC to supply a 12V AC SELV bathroom extractor fan? - Page 1
Forum section: electronics / repair

author: mp
author_rank: Newbie
timestamp: June 22, 2023, 01:03:27 pm
content: I have a new low voltage 12V AC SELV bathroom extractor fan that somehow needs to be wired to an old 14V AC transformer (measured with a voltmeter). The transformer was designed to be 12V AC but is delivering 14V. The 14V cable end sits in a 100mm wall duct ready to wired to a fan. I have no access to the transformer hidden in the ceiling above the bathroom to be able to replace it.What's the best way to drop the 14V AC to 12V AC, just prior to the fan wiring terminals please?

author: IanB
author_rank: Super Contributor
timestamp: June 22, 2023, 01:17:17 pm
content: Just connect it. It is normal for a "12 V" transformer to measure a slightly higher voltage when not under load. The voltage will drop when the fan is running, and the fan will not care if the voltage is up or down by a volt or two above the nominal value.If you actually measured 12 V on a 12 V transformer you would have to assume the transformer was faulty.

author: Jeroen3
author_rank: Super Contributor
timestamp: June 22, 2023, 01:26:15 pm
content: Connect the fan? The transformer will drop because it's loaded.Transformers usually have higher open circuit voltage, doesn't need to be that exact. Does it?

author: mp
author_rank: Newbie
timestamp: June 22, 2023, 02:02:40 pm
content: Great, thanks both for your help. I just didn't want to risk damaging or reducing the life expectancy of the fan components. So 14V ac no-load voltage is fine, great 😃If you have any hint or tips to add? Maybe something I should had asked but didn't.Thanks.

author: DavidAlfa
author_rank: Super Contributor
timestamp: June 22, 2023, 06:29:10 pm
content: Transformers willl show way higher voltage than nominal when unloaded, measure again but connecting a 100ohm resisto.If mesuring 14V unloaded, the working voltage will be maybe 9-10V, no more!Just connect it, even if it was really 2V more, it wouldn't make any difference.

author: hussamaldean
author_rank: Unknown
timestamp: June 22, 2023, 06:34:08 pm
content: Hi,just connect the fan directly.It won't be an issue.
[SOLVED]How to enter calibration mode - TEXIO (kenwood) PW18-1.8AQ power supply - Page 1
Forum section: electronics / repair

author: daisizhou
author_rank: Super Contributor
timestamp: April 30, 2025, 03:19:34 am
content: Hallo everyoneI have a TEXIO power supply model PW18-1.8AQ.I found that the voltage was a little offset, I tried to calibrate it according to the manual,But the actual host was not as described in the manual.And it is not possible to select the output setting as described in the manual, the output port will output voltage.I don't know how to calibrate it, if anyone could help me it would be greatly appreciated, thanksPWA-series service manual-->https://www.manualslib.com/manual/1194439/Kenwood-Pw-A-Series.html

author: zhangwei638
author_rank: Newbie
timestamp: May 28, 2025, 12:59:43 pm
content: output select只是使能输出通道，这个选了校准通道后自动使能了（亮灯），缺少的一步是要按 STATUS key，显示OFAdj，这个时候就可以通过旋钮调调压了（调整到电压100%量程）调好电压后，按MAIN OUTPUT key，电源输出电压调整旋钮修正到你要的电压值按Memory Key保存，机器自动关闭MAIN OUTPUT输出再按STATUS key，显示OFAji，调节10%电压范围按MAIN OUTPUT key，再次输出电压调整旋钮修正10%电压范围按Memory Key保存，机器自动关闭MAIN OUTPUT输出机器自动退出该通道校准模式

author: daisizhou
author_rank: Super Contributor
timestamp: May 28, 2025, 01:20:54 pm
content: Thank you, I'll give it a try谢谢，我试试，若遇到困难在向你请教，感谢

author: daisizhou
author_rank: Super Contributor
timestamp: May 29, 2025, 08:12:48 am
content: Quote from: zhangwei638 on May 28, 2025, 12:59:43 pm奇怪，我按按 STATUS key后并不会显示OFAdj,并且就算显示的话也应该是显示OFAJ的吧？Strange, when I press the Status key, it doesn't display OFAdj, and even if it does, it should still display OFAJ, right?

author: zhangwei638
author_rank: Newbie
timestamp: May 30, 2025, 10:00:04 am
content: 我是校验完后凭记忆记录 ，所以有的细节有点模糊，大体流程没问题举例选择通道1的电压校验模式，显示Adst U--1按Memory后，显示---- ----按Status，显示OFAJ 0.00开始校验全量程，按Memory保存开始校验10%量程，按Memory保存机器自动退出该通道校验模式，显示Adst U--1，此时你可以选其他通道进行校验

author: daisizhou
author_rank: Super Contributor
timestamp: May 31, 2025, 04:07:52 am
content: Quote from: zhangwei638 on May 30, 2025, 10:00:04 amThanks, all calibrations need to be completed once, including voltage and current calibration感谢，需要全部校准一次才能完成，包括电压和电流的校准
How to find keyboard cable + - ends - Page 1
Forum section: electronics / repair

author: hummerjanne
author_rank: Regular Contributor
timestamp: October 27, 2023, 08:38:41 pm
content: How to find keyboard cable + - ends My question is yes, the cable is broken and how can I find the + - ends?

author: Swake
author_rank: Frequent Contributor
timestamp: October 28, 2023, 02:49:22 pm
content: You'll have to give more details about what keyboard it is and how it is connected

author: ebastler
author_rank: Super Contributor
timestamp: October 28, 2023, 03:03:40 pm
content: Assuming it is a USB connection, which is by far the most popular today -- did you try Google or Wikipedia?https://en.wikipedia.org/wiki/USB_hardwareIf by + and - you mean the +5V supply voltage and GND, they are on pins 1 and 4 (the two outermost pins in a USB A connector). If you mean the data lines, D+ and D-, they are on pins 3 and 2 inbetween.

author: hummerjanne
author_rank: Regular Contributor
timestamp: October 29, 2023, 09:07:18 am
content: I solved the problem but I saw that no part was working on the keyboard motherboard except the IC silicon so I replaced it, I used the LED to find the +- cable and found it this way. The problem was with the keyboard motherboard, not the cable. Almost most of the parts did not work. I removed the SMD parts and replaced them with high value resistors and capacitors.

author: ebastler
author_rank: Super Contributor
timestamp: October 29, 2023, 09:53:16 am
content: You mean, all the passive components (resistors and capacitors) on the keyboard's PCB were bad, but the active IC was OK? That is very unlikely. Maybe there was just a single bad component or a bad solder joint somewhere?In any case, glad you got it back into working order!

author: hummerjanne
author_rank: Regular Contributor
timestamp: October 29, 2023, 03:17:50 pm
content: Yes, the resistor was not working. It connects to LEDs. Luckily I solved the problem, but one thing I noticed was that it wasn't giving any value. The resistance was showing 0 and the multimeter was beeping. The capacitor was not giving any value.
How to find out what LED part is used in LG TV - Page 1
Forum section: electronics / repair

author: AndreyS
author_rank: Regular Contributor
timestamp: December 25, 2021, 04:24:23 pm
content: Hi there,I've got LG 39LN5300 with some of backlight LEDs burnt out.The text on the strip says: LG Innotek POLA2.0 39" B Type Rev 0.0 2012.11.14The text on the strip says:LG Innotek POLA2.0 39" A Type Rev 0.0 2012.11.14The LED SMD dimension are 2835 or 3528, the voltage is 3V, since nominal_LED+/#of_LEDs 133V/36=3.69V. The current is 0.37A, thus 0.37*3.69= 1.36 W. Thus LEDs power should be about 2W.But what color temperature are LEDs? I couldn't find any information on that.Of cause you could've said to buy LED strips and just replace them, but original strips are not to be found, and chinese of questionable quality - I don't want them. I what to order good q LEDs from mouser.

author: strawberry
author_rank: Super Contributor
timestamp: December 26, 2021, 02:51:18 am
content: can get LED in same case from mouser digikey. I think TV LEDs officially no one sellsonce got chinese LEDs for ''original LG TV'' melted during hot air soldering(probably PVC...) so bought (~0.5EUR) Osram natural white... but turned out yellowish but still worksI bet its more closer to 1.5W (LED die is kept about 100C)sometimes polarity is reversed(read technical drawings carefully)

author: AndreyS
author_rank: Regular Contributor
timestamp: December 26, 2021, 08:38:05 am
content: unfortunately, this is the highest power white LED I could find on mouser:https://eu.mouser.com/ProductDetail/Cree-LED/JE2835AWT-00-0000-000A0UF957E?qs=chTDxNqvsylKm3K1zKH%2F%2FQ%3D%3Dit's 240mAnot enough

author: ealex
author_rank: Frequent Contributor
timestamp: December 29, 2021, 06:13:03 am
content: helloi don't think you can replace the leds:https://youtu.be/lM8AyRw9A38?t=251andhttps://ae01.alicdn.com/kf/H133522a9289143ee926b0d1f6bc18b8co/8-PCS-set-LED-Backlight-strip-For-LG-39-inch-TV-39LN5300-39LN5400-HC390DUN-VCFP1-21XX.jpgthey're more like a bare die + phosphorus coating on the pcb strips, + the lenses stuck over themyou can find the led strips on ebay (filter by location) or even local shops.

author: flolic
author_rank: Frequent Contributor
timestamp: December 29, 2021, 08:22:53 am
content: Don't waste your time replacing LEDs on the original strips, just buy replacements strips, but make sure that they are on the aluminium based PCB.Original PCB is phenolic with terrible thermal conductivity and that's the reason of LED failures. Also you will have almost impossible mission putting lenses back in the exact right position, and failure to do that will result with bright rings on the picture.Don't ask me how I know all that...Replacement LED strips can have slightly different color temperature than original, but that can be compensated in TVs service menu.
How to find replacement Li-Ion battery: M-Audio Microtrack II - Page 1
Forum section: electronics / repair

author: stefan_o
author_rank: Regular Contributor
timestamp: March 03, 2025, 01:20:13 am
content: Hello,I've got a M-Audio Microtrack II with a (almost) dead battery. It's 3.7V li-ion flat battery with dimensions of 4.5mm x 50mm x 58mm that is quite easy to replace, but anything even slightly thicker will not fit. I assumed finding a replacement is quite easy, but so far it's a nightmare: I couldn't find a single store where I can search for li-ion batteries by size. Nowhere I had the nice parametric search of Mouser/DigiKey. I can find hundreds of li-ion batteries at Amazon, but finding one that fits seems impossible.Does anyone know of a store where I can find a battery with those maximum dimensions (that will ship to the EU)?Best regardsStefan

author: Chalcogenide
author_rank: Regular Contributor
timestamp: March 03, 2025, 09:29:31 am
content: You should be able to find them on Aliexpress.Generally for "pouch" style batteries, the sizing is code as XXYYZZ, where XX is the thickness in tenth of mm, YY is the width in mm, and YY the height in mm. So you might want to look for a 405055 (that I can find relatively easily on Aliexpress).Beware that shipping may take a ridiculous amount of time, as batteries often need to be shipped via ground/sea.

author: stefan_o
author_rank: Regular Contributor
timestamp: March 03, 2025, 11:19:51 am
content: Thank you very much! I will order one of those, even if it takes 10 weeks to deliver. I realized the numbering scheme, but I couldn't find anything on 455058, I tried adjusting the numbers a little but I didn't find a combination that gave me any result
How to fix loose BNC connectors on Philips PM 3055 scope - Page 1
Forum section: electronics / repair

author: Kevin H
author_rank: Contributor
timestamp: September 29, 2023, 06:44:21 am
content: I have a Philips PM 3055 scope which works fine, but the three BNC connectors on the front panel are really loose. There is no obvious way of getting the front panel off. Does anyone have any ideas, or experience with this scope?

author: C-47
author_rank: Regular Contributor
timestamp: September 29, 2023, 09:17:26 am
content: That Philips scope is very much a push together plastic housing, take care when pushing tabs to get it released as the plastic hardens with age and easily breaks. I had mine apart some years ago and the specifics are a bit hazy, but the attached photo is the rear of the front panel and it looks like the 2 screws hold that on and I suspect the BNC connectors are behind that and they should be held on with a nuts. The open area is where the internal battery would go, which I presume your unit doesn't have. Alan.
How to fix switching noise (acoustic noise) from power supplies?  - Page 1
Forum section: electronics / repair

author: Odd
author_rank: Regular Contributor
timestamp: February 17, 2020, 09:11:32 pm
content: I just received two ViewSonic displays I bought, and while they otherwise perform as expected, there is a rattling noise from some inductors, I can imagine, inside.In a very quiet environment, like my office, this drives me crazy, I could easily return them, but it would be cool to fix.Frequency may be below 5khz, in terms of db it is not very loud.So, how does one proceed on quieting a noisy switch-mode PSU? - Does it work to locate the correct coil(s) and ...epoxy them?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 17, 2020, 09:38:03 pm
content: Standby or active?If standby, it's probably pulsing infrequently to maintain voltage. The pitch can vary with mains supply voltage and will vary with load. Not much you can do here: the noise is likely due to magnetostriction in the core. That is, the core itself is straining due to applied magnetic field. The core is quite stiff, so it's not like you can keep it from straining by putting rubbery goop on it. About all you can do is add padding to absorb the sound (which may however still involve rubbery goop, say to dampen the PCB). Be careful with padding, so as not to block airways.If active, it may still be the above, if not on the main supply(ies) then on an aux supply or something perhaps. Otherwise, it may be poor compensation, which may suggest aging electrolytics, or poor component choice in the first place.Heh, also, if it has powered speakers internal or attached, those could be squealing, for similar or different reasons.Tim

author: David Hess
author_rank: Super Contributor
timestamp: February 18, 2020, 05:33:58 am
content: Quote from: T3sl4co1l on February 17, 2020, 09:38:03 pmJust to elaborate on this, high ESR from worn out capacitors can cause false triggering and noisy operation of the switching controller resulting in audible subharmonic oscillation. This is good because many of there other causes would require redesign.

author: Odd
author_rank: Regular Contributor
timestamp: February 18, 2020, 08:58:59 am
content: the noise is when active.The pitch changes with overall brightness, I suspect it is not the main PSU, but CFL supply.I plan to return the displays and get some other brand/series.