hybridfree/eevblog-posts huggingface dataset:
Switch mode power supply showing double what it should on all rails. - Page 1
Forum section: electronics / repair

author: PoDuck
author_rank: Regular Contributor
timestamp: March 04, 2018, 02:49:56 am
content: I have a switch mode power supply on a TRS-80, and I had some other issues with it, such as the SCR (Q6) blowing for an unknown reason, and a 30V zener (VR1) blowing because apparently this power supply must have a load on it at all times, but now that those issues are sorted, I have another problem, which is that I am getting double what I should be getting for power. The 12 volt rail reads 24 volts, the -12 volt rail reads -24 volts, and the 5 volt rail reads 10 volts. It is pretty much exactly double what it should be. I am thinking that should be a clue, like maybe a shorted resistor in a voltage divider somewhere, but for the life of me, I'm not sure where it would be.The schematic for it is here:at https://ia600901.us.archive.org/14/items/TRS80Model4PServiceManual/TRS80%20Model%204P%20Service%20Manual.pdfThe schematic for the board I'm working on is on PDF page 164, which is page 161 of the manual.When I run this board, there are a couple resistors that get extremely hot, but I'm certain that it is because they are dissapating more power than the circuit was designed for. I only run it for a short time to do tests, then turn it off so it can cool down. I am sure that even this is not good for things.I have checked the test points D and E with the oscilloscope, and all the wave forms look like the pictures say they should, except that I have to use a higher volts per division setting to see it, which is likely because things are running at about twice the voltage they should. The sawtooth from pin 5 of the PWM is around 36Khz, but I don't know what it should be at. I also don't know what duty cycle I'm supposed to be finding. The reference voltage on pin 12 is 4.95 volts, which I am assuming is supposed to be 5 volts and within specs, but I don't know.The odd thing is that I am not detecting DC voltage on pins 1 and 2, but I do detect an AC voltage of between 4.5 and 6.3 volts, depending on when I test them. I am assuming that this is showing as AC because it is a square wave signal, but I don't know.So, it appears that the PWM is probably okay, but likely getting the wrong inputs. I just don't know where to look, and I really don't want to start taking every resistor off the board to test it. Am I even correct in thinking it could be a bad resistor, or am I completely stupid?Anyway, any help would be appreciated.

author: 0xfede
author_rank: Regular Contributor
timestamp: March 04, 2018, 09:17:52 pm
content: Hi PoDuck,this seems to be the common failure of the optocupler (in your case is a 4n35 labeled as U2).Hope this helps.Best,0xfede
Faulty power supply? High output noise. (Matsusada PK-80H) - Page 1
Forum section: electronics / repair

author: TheAmmoniacal
author_rank: Unknown
timestamp: March 04, 2018, 06:58:07 pm
content: I bought a small high-voltage power supply some time ago (320 V DC, 500 mA, 80W) for use in electrophoresis (biology stuff), as I bought it used on eBay I did some simple health checks and cleaning. In measuring the output on the scope I noticed quite a bit of noise and ripple, is it faulty?According to the specifications the ripple is max 20 mVrms and 1 mArms. I don't have a good unit to compare it against, and not sure how much ripple and noise I should expect from a small HV switching supply like this, anyone else know if this is normal?This how I measured it:This is what it looks like in CV mode (19 V), 499 mA. Audible whining noise.This is CC mode (20 V), 500 mA (same scale as the one above)
Fluke 85 - fading display - Page 1
Forum section: electronics / repair

author: newbie666
author_rank: Regular Contributor
timestamp: March 02, 2018, 07:43:24 am
content: My fluke started loosing some segments on the display, is it a known issue? Any ideas if there's a fix doable by oneself?Best regards

author: HecticZA
author_rank: Contributor
timestamp: March 02, 2018, 08:15:09 am
content: Afik this is a known occurrence.Lots of info on YouTube, but this is the first one I saw.https://youtu.be/6RBug_9Y47sSent from my SM-N950F using Tapatalk

author: HecticZA
author_rank: Contributor
timestamp: March 02, 2018, 08:30:21 am
content: Same result, but different approach.Not sure which is the better / correct option.https://youtu.be/ejvfzfGHz0cSent from my SM-N950F using Tapatalk

author: mzacharias
author_rank: Frequent Contributor
timestamp: March 02, 2018, 10:31:06 pm
content: If you plan to clean the circuit board pads which contact the elastomers - be extremely careful in removing the "top shield" with the little clip things that hold it to the board. The little clips break real easy. If this happens, it's not a deal-breaker, but better to be careful.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 03, 2018, 03:47:32 am
content: Quote from: newbie666 on March 02, 2018, 07:43:24 amYes, known issue. Easily fixed. Seehttp://mrmodemhead.com/blog/fluke-8x-faded-lcd/

author: newbie666
author_rank: Regular Contributor
timestamp: March 04, 2018, 06:51:51 pm
content: Thanks a lot for all the replies. I'll attempt a fix next weekend!
Diagram needed - Page 1
Forum section: electronics / repair

author: sidspop
author_rank: Contributor
timestamp: March 03, 2018, 10:29:00 am
content: Connections diagram for a Kenwood KAC-901 car amp. just the connections.There appears to be precisely nothing on the internet to do with how it is connected.Thanks

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 03, 2018, 10:45:57 am
content: Here you can download the schematic, that should help:https://elektrotanya.com/kenwood_kac-901_amplifier_sch.pdf/download.html

author: Bratster
author_rank: Frequent Contributor
timestamp: March 03, 2018, 10:51:21 am
content: Edit: got ninja'd Here's a link to a PDF of the schematic:https://elektrotanya.com/kenwood_kac-901_amplifier_sch.pdf/download.htmlDidn't see anything for installation in a quick Google search but it may be out there.Sent from my Nexus 6 using Tapatalk

author: sidspop
author_rank: Contributor
timestamp: March 03, 2018, 12:23:31 pm
content: already got that diagram, but it's a very poor scan of a photocopy. when blown up the definition (what there is) dissappears

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 03, 2018, 02:35:18 pm
content: Quote from: sidspop on March 03, 2018, 12:23:31 pmI'm not sure what you have been looking at, but the scan is of very good quality and it is easy to see where the connections are.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 03, 2018, 05:39:11 pm
content: https://www.amp-performance.de/518-Kenwood-KAC-901.htmlfor photosi had one of theses in the past, normally you would connect the din for left an right and the remote power up pins, you have din to rca plug converters too, and in one photo you see the output plug with the power pins ...

author: Bratster
author_rank: Frequent Contributor
timestamp: March 03, 2018, 06:34:12 pm
content: Quote from: sidspop on March 03, 2018, 12:23:31 pmDid you actually download the PDF file from linked webpage?I had no problem zooming in on it and seeing everything just fine.The image on the page however is just low resolutionSent from my Nexus 6 using Tapatalk
What's this component? - Page 1
Forum section: electronics / repair

author: ElektroQuark
author_rank: Unknown
timestamp: March 04, 2018, 10:16:35 am
content: It's from a PHILIPS LED tube power supply.

author: keymaster
author_rank: Regular Contributor
timestamp: March 04, 2018, 01:55:14 pm
content: npn transistor(http://www.crhj.com.cn/uploadfile/z6081blxt8g4963qsoa7.pdf)its in Chinese so google translate (https://translate.google.gr/translate?sl=auto&tl=en&js=y&prev=_t&hl=el&ie=UTF-8&u=http%3A%2F%2Fwww.crhj.com.cn%2Fuploadfile%2Fz6081blxt8g4963qsoa7.pdf&edit-text=&act=url)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 04, 2018, 02:26:06 pm
content: ^ That seems to be the ticket.Similar to an MJE13003, though a bit higher voltage. There's plenty of "Switchmode" style BJTs out there that will drop in.Tim

author: ElektroQuark
author_rank: Unknown
timestamp: March 04, 2018, 08:38:38 pm
content: Curious PHILIPS using a Chinese NPN.Thank you.
MSF Anthorn ("Rugby") radio-controlled clock -all segments lit - Page 1
Forum section: electronics / repair

author: FrankE
author_rank: Regular Contributor
timestamp: March 02, 2018, 05:43:55 pm
content: I've a radio-controlled clock on my bench just nowIt was cheap from Lidl 15 years ago and switches between MSF Anthorn ("Rugby") @60kHz and DCF 77 for CET @ 77kHzIt's displaying all segments on and intermittently going to the normal boot.The IC is sealed. I've ordered some new caps for it, some new ribbon for the DCF/MSF switch + reset tactile switch (buzzed out and not stuck on reset)..I'm not sure if the xtal is working, it's reading 50Hz.which doesn't seem right What would be a typical value for such a xtal?There's a plastic-coated bead-shaped device for the temp, not sure if the unit ever displayed humidityWould such a sensor if for only temperature on such a cheap clock be a thermocouple, or what?

author: Jeroen_Bezemer
author_rank: Contributor
timestamp: March 02, 2018, 05:55:57 pm
content: Quote from: FrankE on March 02, 2018, 05:43:55 pmTemp sensor : Probably pt100 or pt1000Just measure resistance at room temp and you know...Verstuurd vanaf mijn SHIELD Tablet K1 met Tapatalk

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 02, 2018, 07:17:48 pm
content: Quote from: FrankE on March 02, 2018, 05:43:55 pmA typical RTC crystal should be 32KHz. 50Hz sounds like mains is getting in somewhere.

author: Gyro
author_rank: Super Contributor
timestamp: March 02, 2018, 07:18:23 pm
content: Quote from: FrankE on March 02, 2018, 05:43:55 pmMost likely a thermistor.

author: FrankE
author_rank: Regular Contributor
timestamp: March 02, 2018, 08:40:54 pm
content: Many Thanks.I might have bead thermistors and Pt100s kicking about somewhere. Would the IC of these types of thing look for the sensor when booting?I ordered 32.whatever kHz xtals anyhoo as 50 seemed wrong. Perhaps EM coupling from my supercheap Maplin wibbly-wobbly mag lamp.I ordered from RS last night in a hurry to meet the 20:30hrs cutoff for next day. Apparently 20:28hrs was cutting it too fine so it'll be Monday now.Thanks again
Multimeter dial quality question. (Anyone has the Owon B35?) - Page 1
Forum section: electronics / repair

author: zdelarosa00
author_rank: Regular Contributor
timestamp: March 07, 2018, 05:13:30 am
content: My past multimeter died on me because the dial had damaged contacts, I tried to repair the too fragile copper strip and ended up destroying the whole dial.I had a VC99, I am planning on buying the replacement part, although shipped costs almost like a new VC99, but then i would have a new one and a perfectly working one without dial for parts (a waste if you ask me).That multimeter works pearls for me.I want to either find a way to replace (easy buy) or repair those (dial and or contacts), or a reliable multimeter which brand sells the dial part with contacts as a replacement for decent money (not a new multimeter price).Anyone has something to suggest on the issue or comment about the Owon B35 dial quality? (It's on my watchlist for a new multimeter if I can trust this dial issue. The web page looks so far so good. Looms reliable, already asked if they sell the part while I ask here. Website is at least not in mandarin).Enviado desde mi SGH-I317M mediante Tapatalk

author: FrankE
author_rank: Regular Contributor
timestamp: March 07, 2018, 05:54:53 am
content: In my experience when the traces for the dial are gone, the meter's gone.
Tektronix 496 - Page 1
Forum section: electronics / repair

author: wd5jfr
author_rank: Regular Contributor
timestamp: December 09, 2017, 12:18:32 am
content: Just got one at an area hamfest, was told it worked but didn't have any power or time to check. Was told it displayed 2 meter handhelds with a paper clip for an antenna. Very nice physical shape not beat up, good cry display.Got it home and Cal out -20dBm 100mHz shows about 2.5 grid squares while on my signal generator set for 0.0 dBm it shows about 3.2 grid squares across its 1.8 GHz spectrum on 10dB/div and doesn't increase at 0.0dBm or +10dBm. Response flattens out 3.2 grid square. Wild guess is that the mixers might be OK since it reads the same up tp 1.8 GHz.and the fault is in the front end either attenuator or whatever it uses for an amp. If this is the case are parts or good replacement PCB assemblies available? The free PDFs are not easy to read, so I'll see if I can find an real original paper manual, anyone have one for sale?I haven't opened it up yet, still trying to make sure I'm using it correctlyIs this a common problem? Any tips or suggestions appreciated.Hank WD5JFR

author: wd5jfr
author_rank: Regular Contributor
timestamp: March 01, 2018, 10:42:31 pm
content: Got it opened up and all the voltages are in spec, no connectors loose. What I've noticed is the Digital Storage buttons, View A View B, don't light up when pressed but do flash when I first turn the unit on. I wonder if this might be reason that's more that half deaf. Any suggestions appreciated.ThanksHank WD5JFR

author: tggzzz
author_rank: Super Contributor
timestamp: March 01, 2018, 11:27:33 pm
content: Artek have the manuals; spend $15 and download all four of them. I am a satisfied customer.http://artekmanuals.com/manuals/tektronix-manuals/
Corsair 550D case USB3 front port -part ID?. - Page 1
Forum section: electronics / repair

author: FrankE
author_rank: Regular Contributor
timestamp: March 02, 2018, 06:09:47 pm
content: One of the ports on my Corsair case is not working. Could be the trace, a poor joint or the driver. I think a :- flash drive was hit, so impact damage.I'm not keen on having my PC switched off, and I was going to replace the whole port, preferably one with a backlight.Anyone know a port with similar mounting and dimensions?Thanks
Relay buzzing unless hooked after ESP8266 boots up. - Page 1
Forum section: electronics / repair

author: nardev
author_rank: Unknown
timestamp: February 23, 2018, 05:22:16 pm
content: I believe that it would be proper way to put the whole project description but i hope it might be enough for someone with experience.So, very simple thing.I power up ESP8266, it boots, everything works fine.I hook one of those cheap songle relay module boards (i tried other relays too, same thing) and controlling the relay works perfectly. No issues there.However, if i leave it like that and restart EPS (power down/up), the esp never boots up, and there is silent buzzing from the relay.Probably this might be all you need:Between the ESP IO pin and relay board i have 1K resistor, 2n3904 NPN transistor and it switches 5V relay powered from external 5V.Any clues?

author: nardev
author_rank: Unknown
timestamp: February 23, 2018, 05:25:43 pm
content: Quote from: nardev on February 23, 2018, 05:22:16 pmJust as i wrote this, i realized.. why the hell do i have only 1K therelol.. doesn't buzz any more...

author: ArthurDent
author_rank: Super Contributor
timestamp: February 23, 2018, 05:58:33 pm
content: See you got it working. Maybe you have already seen this but there is good information here for future reference.https://www.forward.com.au/pfod/HomeAutomation/OnOffAddRelay/index.html#single5V

author: nardev
author_rank: Unknown
timestamp: February 28, 2018, 05:58:11 pm
content: THnxp.s. one of the issues was that MCU had pull-up on the pins i used my default.. so.. it even made more confusions..
Samsung 60" plasma power supply STBY issue - BN44-00514A - Page 1
Forum section: electronics / repair

author: avsion
author_rank: Newbie
timestamp: February 27, 2018, 11:32:15 pm
content: Hi Guys,I need your expertise with repairing my TV power supply board, I'm trying to find the issue with the standby circuit, ATM i don't have any 5v STBY and 4.3V PS-ON coming to CN801 i.e nothing on the cold side.i follow the hot side DC voltage from the BR>PFC>Filter Caps>STBY Transformer via ICE3BR2565JF flyback circuit and i'm getting 330V on the hot side of the transformer. i also get 330 volts coming in to one of the ICE3BR2565JF pins.when checking the other pins on the ICE3BR2565JF i don't get any 18v coming in from the ICE3BR2565JF flyback circuit to start the ICE3BR2565JF. So i have a good feeling that the issue is the ICE3BR2565JF but this area was covered in silicon, when removed i found few faulty components such as CX895, DX859 and damaged printed circuit which i soldered wire, also DQ804 is a suspect, see attached images.ICE3BR2565JF can be download from this linkhttps://www.infineon.com/dgdl/Datasheet_ICE3BR2565JF_v20_11Sep08.pdf?folderId=db3a304412b407950112b4182a3d24f8&fileId=db3a30431ce5fb52011cf40f584204eathe problem now is as follows:1. as i don't have the diagram to find out the part numbers so i can't order the DQ804, CX895 and DX8592. I cant follow the damaged printed circuit as there are black marking covering it, so i can't confirm the path to fix.Is there any way to find out the part numbers and the damaged circuit path of the above without the diagram?Till now i have tested and replaced with new ones all the following:1. All the CAPs on the board (except the HV Hot and cold big filter caps)2. DS810 small signal diode BAV703. QS802 & QS804 Switching Fets4. Tested all the main diode, DQ804 was measuring 0.200v when all the others UF4007 was measuring 0.500vFYI i just started a month ago learning basic electronics (very late stage ),SMPS Circuits as a hobby and knowledge, i'M building up my LAB equipment ATM.Thank you for your help.

author: avsion
author_rank: Newbie
timestamp: February 27, 2018, 11:33:25 pm
content: More photos attached
Samsung Galaxy Young 2, digitizer not working - Page 1
Forum section: electronics / repair

author: panoss
author_rank: Frequent Contributor
timestamp: February 27, 2018, 04:07:29 pm
content: In a Samsung Galaxy young 2 I replaced the LCD screen + digitizer.The screen works fine, but the digitizer does not work at all.I also tried it with two other used digitizers without any success.So, I did a factory reset (volume up button + power button + home button -> Facory reset->Wipe data etc) but at some point I have to enter some data through the keyboard but the digitizer still does not work.So the factory reset is left unfinished.A photo of the connector of the digitizer to the LCD can be seen in the attachment.Any help is welcome.(the digitizer and the LCD screen isbought from Aliexpress, if this is of any importance)
Tektronix 2445B NVSRAM Image - Page 1
Forum section: electronics / repair

author: ahsuilim
author_rank: Newbie
timestamp: February 27, 2018, 12:17:04 am
content: Hi,This is my first post here. Just bought a used 2445B early model SN:B010xxxx, upon power up I saw test 04 failure 10. Seem like a CAL NVSRAM problem. Are there any NVSRAM image for the 2445B early model available? I know there is NVSRAM image for later model > SN:B050xxxxThanks for your help.
Yorkville 100watt Mixer/Amp - Replaced Transistors, distorted volume. - Page 1
Forum section: electronics / repair

author: jgrilo
author_rank: Newbie
timestamp: February 24, 2018, 08:43:07 pm
content: Hey all, new here and hope for some direction and assistance. Here is the backstory.This amp has a bass/treble pot (50k linear) and the shaft was broken. I wanted to replace for cosmetics, amp functioned just fine.Bought 2 pots from digikey and replaced. They were 50k linear.Fired amp up and it didn't quite sound the same, played with bass/treble and turned amp up and then POP. Blew the 5amp fuse.I replaced the fuse and every time i powered on the fuse pops again. Took it to a buddy and we decided I probably fried the 2 output transistors (MJH11018 and MJH11017). Now when i was testing/playing I never put the transistors back on the metal frame so we assumed they overheated and fried.For added measure we replaced the BC550C transistor as well.Order 2 orig 50k pots from yorkville and replaced them as well.The leads on the BC550C were too long and was shorting out, we figured this out as BD139 was getting really hot. Fixed the leads and now the amp runs and sounds good at low volume. No fuse issues.As soon as we push the amp more than 30% volume the sound is distorted and sounds terrible. No matter what input/channel.The headphone jack works just fine and i can drive the amp loud and the headphones don't sound distorted.However as normal the amp is not right, i don't know what i'm missing and what to do next? We're thinking of replacing BD139 as maybe the heat ruined the chip.Here are the 2 transistors i replaced from DigiKey, slightly different spec but we were told they should be just fine.https://www.digikey.ca/product-detail/en/on-semiconductor/MJH11022G/MJH11022GOS-ND/919545https://www.digikey.ca/product-detail/en/on-semiconductor/MJH11021G/MJH11021GOS-ND/919544I've also attached a schematic.Could we somehow have switched up the NPN PNP transistors? if so would the amp work at all?any tips would be super helpful! thank you!!

author: Armadillo
author_rank: Super Contributor
timestamp: February 24, 2018, 09:00:01 pm
content: Can you show photos TOP and BOTTOM of the pots you have done the soldering.Please tell us what measuring instruments do you have at hand.?

author: Andy Watson
author_rank: Super Contributor
timestamp: February 24, 2018, 09:10:01 pm
content: Quote from: jgrilo on February 24, 2018, 08:43:07 pmUnlikely - I think it would have smoked again if the transistors were swapped.Do you have the facility to measure the voltages at TP1 and TP2? Also, do you have another amplifier to check the loud-speaker?

author: anachrocomputer
author_rank: Regular Contributor
timestamp: February 24, 2018, 11:35:19 pm
content: The fact that the headphone output is OK must be a clue. Can you trace that part of the circuit and see whether the signal to it passes through the parts you've replaced?

author: Ray Gianelli
author_rank: Contributor
timestamp: February 25, 2018, 11:52:59 am
content: Did you check the output transistor emitter resistors?
Maybe We Can Figure This Out Together - Page 1
Forum section: electronics / repair

author: OldSchoolAES
author_rank: Newbie
timestamp: February 26, 2018, 05:37:59 pm
content: Hello Everyone!So I'm trying to get an old piece of equipment from 1974ish to 1981ish time frame, the circuit diagram dates it to 1981, to come back to life where I work. It's basically been abandoned for years and was covered in dust when I found it. I happened to find the dust covered manuals with circuit diagrams for this multicomponent machine.What's this machine you ask? It's an old school PHI 545 AES or Auger Electron Spectrum analyzer built in 1974 and there are at least two parts of the thing that aren't working properly.If I upload images of the circuit diagrams and a list of components on the boards in the first component of the system and tell you what it's not doing properly, according to the manual, do you think you might be able to help me figure out what in the world popped on the board? I've been at it for a few weeks now and I've run into at least one component that I've had to replace, an MHQ6002.This is basically a project to keep me busy during my down time at work and is pretty much useless for us as a lab.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: February 26, 2018, 06:02:18 pm
content: Welcome to the forumsIt would be nice to rename your thread to a more specific title. You can edit your initial post and also edit the subject line there. I suggest something like: "PHI 545 Auger Electron Spectrum Analyzer: Help needed." or similar. That way people can already tell if it is a thread for them worth looking at or not.The more information you can share, the more likely it will be you get pointed in the right direction.It definitely helps if you can provide schematics, decent quality photos of the device / PCBs / parts you are working on and a description of what you already measured/did/tried.Kind regards and have a nice time here,Frederik

author: rhb
author_rank: Super Contributor
timestamp: February 26, 2018, 06:56:39 pm
content: Someone started a thread, "Has any tried to build a mass spectrometer" or similar title. One of the first replies was from someone who had built two! A low budget academic instrument and a high budget commercial instrument.Edit the title. You might even get a reply from the designer or a factory technician. It's a pretty amazing group of people.
Repair of 8A pb-battery charger. Unkown part? - Page 1
Forum section: electronics / repair

author: Snake____1
author_rank: Contributor
timestamp: February 25, 2018, 10:12:18 pm
content: Good evening people.I'm at a loss trying to repair a charger. It's based off a switch mode power supply, and output just pulsates. I have checked all diodes, main resistors, optocoupler and more...I get 350v DC on the main side, but on the secondary side it pulsates up to ~3v...I have a TO-220 component on the secondary side I can't identify, hope someone can pitch in here... (See photos) "markings are: T410 BV4715 (Google search renders nothing)

author: 0xfede
author_rank: Regular Contributor
timestamp: February 25, 2018, 10:31:44 pm
content: Hi Snake,it is an AOT410L from Alpha & Omega semiconductor (100V 150A MOSFET)You can find the datasheet here:http://www.aosmd.com/pdfs/datasheet/aot410l.pdfBest,0xfede

author: Inverted18650
author_rank: Frequent Contributor
timestamp: February 25, 2018, 10:33:27 pm
content: http://www.aosmd.com/res/markings/AOT410L.pdf

author: Snake____1
author_rank: Contributor
timestamp: February 25, 2018, 10:45:24 pm
content: Thank you @0xfede!Strange circuitry, seems power goes straight from the SMPS transformer via a relay, to the battery, back through this mosfet and back to the transformer...Almost seems like they are using the mosfet just for the diode...

author: 0xfede
author_rank: Regular Contributor
timestamp: February 25, 2018, 11:00:53 pm
content: You are welcome.I can't say for sure if this is the case but MOSFETs are often used as reverse polarity protection. A good texas instruments application note is here:http://www.ti.com/lit/an/slva139/slva139.pdfBest,0xfede

author: Snake____1
author_rank: Contributor
timestamp: February 25, 2018, 11:56:44 pm
content: Found the faulty component!The OP-AMP on the bottom, the LM324. Changed it and now it's fully functional again
34401A Ohm measurement issues. Solved. - Page 1
Forum section: electronics / repair

author: rolkinas
author_rank: Contributor
timestamp: February 24, 2018, 08:29:04 pm
content: Hello to all!I got my first 34401A. It has impedance measurement issue using front terminals. in lower ranges 2W mode readings are much lower than 4W mode.I checked front/back switch and it is OKThe problem appears to be switch command FXR swithed by front/back switch (telling microcontroller which terminal is activated - front or back) simply connecting U500 pin 25 to gnd (front) or +5V (back).when FXR is tied to gnd - impedance readings are messed up. Conecting FXR to +5V - readings are more or less real. There are measurements in bottom of my post with FXR tied to gnd.Finally I confirmed that only FXR causing measurement failures after soldering 1Ohm resistor past front/back switch and switching FXR by external switch soldered to cut traces.FXR goes directly to uController (U500) passing only 215 Ohm resistor (R512)is seems not much can be done there.Does anyone have experienced such problem?______________________________________________________Measurements results with FXR tied to gnd are folowing:0,001 Ohm 4W mode (leads shorted)0,388 Ohm 2W mode (leads shorted)0,990 Ohm 4W mode0,529 Ohm 2W mode1.092 Ohm checked with Fluke457,472 Ohm 4W mode7,012 Ohm 2W mode7,569 Ohm checked with Fluke45176,46 Ohm 4W mode176,01 Ohm 2W mode167,56 Ohm checked with Fluke451,78584 kOhm 4W mode1,78542 Kohm 2W mode1,7857 kOhm checked with Fluke4517,3600 kOhm 4W mode17,3596 kOhm 2W mode17,359 kOhm checked with Fluke45177,567 kOhm 4W mode177,565 kOhm 2W mode176,56 kOhm checked with Fluke451,56382 MOhm 4W mode1,56375 MOhm 2W mode1,5601 MOhm checked with Fluke45________________________________________________________Any thoughts are welcome.

author: dacman
author_rank: Frequent Contributor
timestamp: February 25, 2018, 02:33:37 am
content: Front/Rear zeros are separately adjustable. I use a Fluke p/n: 884X-Short. I also treat the 34401A terminals with a minuscule amount of mineral oil to both clean them and to help preserve the gold plating on the short. (Metal to metal contact = metal shavings.)Try searching for 34401A threads. There are a few threads on the 34401A with resistance problems.

author: rolkinas
author_rank: Contributor
timestamp: February 25, 2018, 05:02:46 pm
content: Hi dacman, many thanks for hint that back and front are separated calibration wise. It seems that my 34401A was poorly calibrated in past. Calibration sticker on all screws were stopping me from thought about poor calibration (: . After proper zero adjust multimeter works as it should.Regards!
ASUS GTX780 Poseidon - "please power down and connect the pcie power cable..." - Page 1
Forum section: electronics / repair

author: Redmanus
author_rank: Newbie
timestamp: February 24, 2018, 09:15:13 pm
content: Hi Tech-Gods, i'm new here and newbie in electronics too.Long story short:Years ago i have purchased a soldering station (Iron+air blower) and began to learn the basics of reballing, and now i can succesfully reball any VGA even GK110-300/425-B1 chips (the one that got smd capacitors between the soldering points), but later it will not be enough because sometimes a dead card is dead because of a shorted component, so i bought a multimeter (that can measure capacitance too) and began to learn how can i measure basic things with it.Now i have a project i need help with, i need help to find a shorted/malfunctioning component on an ASUS GTX780 Poseidon graphics card.The story of this card:- I have bought it as non-working, it have one green and one red led behind each of the PCI-eX power connectors and when i put in the card the RED leds are normally needs to light up, while the GREEN ones are not until i connect the power connectors, so when i plug in the power connectors the RED lights needs to be in off state while the GREEN ones are lit.- So in the beginning the card generally had a malfunction that when i put it in the PC, the RED ones were lit, and the GREEN ones are lighted up too, but with a lower lumen so like half-power, the PC won't saw the card absolutely, only the fans were working, no picture, the PC booted up with the integrated VGA.- I have began to replace the components on the backside of the card, with components with the same value, especially transistors, found out that one of them marked "702" was faulty, because i have measured the pins in resistance mode and acted differently like the other one marked "702"- Now the led backlights are working perfectly, the PC now recognises the card and can get a picture of "Please power down and plug in the PCI-E power connectors..."- I have measured a lot of things, i'm posting the photos what i have already didAny help appreciated! Thank you
Replacement IC? Availability? - Page 1
Forum section: electronics / repair

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: February 24, 2018, 04:23:37 am
content: Does anybody know if there is a US replacement or equivalent for a Shindengen MTD2005 Motor Driver that can be acquired in short time?China is on vacation.The only eBay source in the US is really China. Thanks.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: February 24, 2018, 12:29:23 pm
content: Google.Well, didn't see those guys. I'll pass it along to the user to order.It's in a machine that is costing money in the down mode.The quickest supplier wins.Shindengen, nice IC'sbut a poor history of available parts.
Ideal 61-734 Current probe plastic knob replacement - Page 1
Forum section: electronics / repair

author: rfengg
author_rank: Regular Contributor
timestamp: February 22, 2018, 09:20:17 pm
content: Have a Ideal 61-734 Current probe ; unfortunately the tabs on plastic knob which sits on the switch selector has been broken due to which I cannot get the plastic knob to sit and lock on the selector switch .I have attached pics of the offending parts.Is there anyway I can get hold of a replacement for this plastic knob?Any mods you guys can suggest to get this to sit on the selector switch; I did contact Ideal and since its an old model, they dont have any replacements
MSI AERO GTX 1060 6GB missing rezistors please  Help! - Page 1
Forum section: electronics / repair

author: Jumper
author_rank: Newbie
timestamp: February 22, 2018, 06:24:51 pm
content: Hello everybodyI received MSI AERO GTX 1060 6GB video card with missing resistors from the bottom of the PCB .Anybody can help me with the value of the 4 missing resistors marked in the picture attached?Thank you in advance!

author: KhronX
author_rank: Frequent Contributor
timestamp: February 22, 2018, 06:36:32 pm
content: To make it a bit more clear, you could've maybe used the names of the resistors that are written right on the board there (instead of R1/2/3/4).

author: Jumper
author_rank: Newbie
timestamp: February 22, 2018, 07:20:52 pm
content: Its a litle bit hard to read the name of the resistors because the PCB is scratched in that place (thats why the resistors are missing ). And thats why I chose to mark&name them by myself.But thank you for the remark i will search for a bether quality picture on the internet and i will add later the name of the resitors .
Cleaning up an old Metcal - Goo Gone? - Page 1
Forum section: electronics / repair

author: knotlogic
author_rank: Regular Contributor
timestamp: February 13, 2018, 09:04:56 am
content: I'm thinking of finally getting round to cleaning up my old, second hand, MX-500. It's got the usual sticker residue, as well as gunk on the bottom from the cheap rubber feet. Would Goo Gone be a suitable cleaner for this? I'm concerned about damaging the anodised aluminium surface.I'll probably replace the power switch too. Looks like the previous owners were using the hot tip of the iron to turn it off.

author: Zucca
author_rank: Unknown
timestamp: February 13, 2018, 09:22:16 am
content: white pencil rubber:and maybe some tiny drops of WD-40.Quote from: knotlogic on February 13, 2018, 09:04:56 amLazy idiot.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 13, 2018, 04:24:55 pm
content: Goo gone hasn't been a problem for me on aluminum, it just leaves that residue that takes a couple passes with a damp cloth to remove. Apply to the cloth instead of directly to the residue to prevent issues with it getting elsewhere and that should be fine.

author: Samogon
author_rank: Frequent Contributor
timestamp: February 13, 2018, 06:55:07 pm
content: Naphta

author: gearshredder
author_rank: Contributor
timestamp: February 22, 2018, 12:24:41 pm
content: I just used isopropanol on mine. I had a bulb go out on each of the ps2e-01 that I've bought so you have to remove the sticker. Maybe similar adhesive?
Kenwood CS-5130 scope trace intesity issue  - Page 1
Forum section: electronics / repair

author: Autronic
author_rank: Contributor
timestamp: February 19, 2018, 11:42:28 pm
content: Hi,Recently purchased a Kenwood CS-5130 sope that has a trace intensity issue. At cold power-up the trace intensity is very high. As the unit warms up the trace intensity will decrease, and the intensity knob needs to be turned to maintain a visible trace. Warm trace intesity is OK, but there is very little rotation left on the knob to increase the intensity.Otherwise the scope functions fine, and has some excellent features.A service manual, or any other assistance resolving this issue would be appreciated.Regards, Chris

author: tautech
author_rank: Super Contributor
timestamp: February 20, 2018, 01:18:49 pm
content: User manual:http://www.cieri.net/Documenti/Kenwood/Test%20Instruments%20-%20User%20Manuals/CS-5135%20-%2040%20MHz%20Dual%20Trace%20Oscilloscope%20(Eng).pdfAs far as I can tell CS-5135 service manual will dohttps://elektrotanya.com/kenwood_trio_cs-5135_40mhz_oscilloscope.pdf/download.html12.7 Mb 18 pagesWait for 'processing' to change to 'get manual'

author: Autronic
author_rank: Contributor
timestamp: February 22, 2018, 11:21:08 am
content: Thanks for the reply, I will look at those links.
SOLVED Datasheet or function for 74ACT124 - Page 1
Forum section: electronics / repair

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: February 21, 2018, 11:08:17 pm
content: SOLVEDDoes anyone have a datasheet or family functional diagram for a 74ACT124?Looked in the usual places, but it can't be found. Googlewants to convert it to a 125 or 241 because I must be an idiot (or so Google thinks). Thanks

author: edpalmer42
author_rank: Super Contributor
timestamp: February 21, 2018, 11:36:45 pm
content: Are you sure it exists?Not all 74x chips exist in all families. I found the 74LS124 (replaced by the improved 74LS629) and the 74S124. They're dual VCOs in the 20 - 80 MHz range depending on the family.Ed

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: February 22, 2018, 03:32:41 am
content: Positive. I'm holding about a dozen or so in my hands right now.

author: amyk
author_rank: Super Contributor
timestamp: February 22, 2018, 03:44:33 am
content: Pictures please.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: February 22, 2018, 03:48:19 am
content: The flip phone is charging right now, but I will take a picture of the lot of them for ID tomorrow.
Ballantine 3028A switch shaft.. or whatever is it called needed - Page 1
Forum section: electronics / repair

author: Ordinaryman1971
author_rank: Frequent Contributor
timestamp: February 21, 2018, 08:17:11 pm
content: Hello, wanted to ask if anybody out there has a Ballantine 3028A that you around that I can get a switch shaft or whatever this part is called from.And if you are asking, it's not like I don't have another meter, I just hate for this thing to be broken and useless because of this little part.I've tried to glue it together but it just doesn't work, I need a replacement.I've included some pictures, take a look please and maybe you just have a switch like this or maybe you know where to get it.

author: sanman
author_rank: Contributor
timestamp: February 21, 2018, 10:36:09 pm
content: If you can't find a suitable replacement I wonder if one could be 3D printed? Maybe check some of the 3D parts sites?

author: Nusa
author_rank: Super Contributor
timestamp: February 22, 2018, 12:43:30 am
content: There are several 3028B parts meters on EBay, which ironically are more expensive than a working 3028A that's selling for $39.99 shipped.I have a 3D printer, but if it were my problem, I think I might try to reproduce it by cutting/shaving down a bit of aluminum stock to the major dimensions and then do the detail work with a dremal and other hobby knives/tools. Thats if the conductivity of aluminum isn't an issue. If it is, then plastic stock and a lot more hand-tool work to avoid melting things.

author: Ordinaryman1971
author_rank: Frequent Contributor
timestamp: February 22, 2018, 12:52:55 am
content: I believe this is a stock switch that was probably used in several applications of the time..... I'm pretty sure somebody will look at it and will know where to find it.Well, I'm looking for this one person, lol. Basically the switch doesn't have to come from another Ballantine meter, it could be coming from... anything of this era.Or maybe somebody has an old stock of those sitting in long forgotten parts box...
VOLTCRAFT DG 20MHZ - Page 1
Forum section: electronics / repair

author: lionelkjh
author_rank: Frequent Contributor
timestamp: February 21, 2018, 06:21:10 pm
content: Good evening everyone! I am looking for the technical documentation (schema) of the VOLTCRAFT DG 20MHZ graphic multimeter (see photo). Can someone help me ?? Thanks for your help!
75W wine (peltier) cooler PSU noise - Page 1
Forum section: electronics / repair

author: nuno
author_rank: Frequent Contributor
timestamp: February 19, 2018, 05:57:26 pm
content: After replacing a bad (high ESR) rectified mains cap on a thermoelectric cooler, it seems to be working but emits this loud noise in attach.Can't pin point the exact source of it. Can't see any sparking or burned spots. What do you think it is? The first "clank" noise it's me unplugging the mains power plug, all others it's the PSU.Thanks

author: nuno
author_rank: Frequent Contributor
timestamp: February 21, 2018, 04:49:39 pm
content: Using the highly sophisticated earing aid tool in attachI pinpointed the noise to a "power" transformer (it's a switching PSU). It seems good, so moving on to check the driving circuit. Meanwhile I found the schematics, the job just became easier
Makita charger flyback controller identification - Page 1
Forum section: electronics / repair

author: nightmechanic
author_rank: Contributor
timestamp: February 04, 2018, 04:13:55 pm
content: Hi All,I have a Makita DC10WD charger (US version) that I opened up to figure out how to convert it to 230V (actually doesn't need any work except the mains plug )During the "reverse engineering" i tried to do I encountered a device with "funny" (custom?) marking - according to its connections it seems to be the flyback controller, its in a SOT23-6 (or similar) package and as you can see marked with a (rather unique according to my experience and web search) 72-63-22 marking.from measurement it is a 65kHz device.out of curiosity - does anyone have any idea what part this actually is?Thanks!

author: xavier60
author_rank: Super Contributor
timestamp: February 04, 2018, 11:17:56 pm
content: No, but Richtek is one possibility. Pin 3 can have different functions between different part number ICs.http://www.richtek.com/assets/product_file/R7735/R7735-04.pdf

author: stj
author_rank: Super Contributor
timestamp: February 05, 2018, 03:48:50 pm
content: check the datasheet for an sp6853that's what is in the Ryobi chargers.

author: duak
author_rank: Super Contributor
timestamp: February 05, 2018, 07:31:40 pm
content: Nothing to do with input voltage but I repaired one like this one from a cabinet shop that had been dropped while charging. The step down transformer broke loose from the PCB and severed one of the secondary wires. This popped the switching FET. I was able to re-attach the wire, replace the FET and make it go again. I can't recall exactly what I did to hold the transformer down but it was probably epoxy and some sort of tie wrap or plastic gee gaw.Cheers,

author: Inverted18650
author_rank: Frequent Contributor
timestamp: February 19, 2018, 12:24:03 am
content: I’ve repaired a pallet of OnePlus Charger from Ryobi and they all had the Top256EN controller.

author: stj
author_rank: Super Contributor
timestamp: February 19, 2018, 08:42:31 am
content: must be newer, if seen inside 4 different charger types and not seen that - so that's the 5th variant!do the idiots still use a pair of schottky diodes in parallel on the output??

author: nightmechanic
author_rank: Contributor
timestamp: February 21, 2018, 08:18:24 am
content: Quote from: stj on February 19, 2018, 08:42:31 amI didn't look at the output (I was mainly interested in the input circuit and whether it needed changes to support 230V operation ).I will check next time I open it up...

author: stj
author_rank: Super Contributor
timestamp: February 21, 2018, 09:22:51 am
content: well that's the common failure point on that variant,i have fixed 12 now - always the same cause.2x 5A diodes in parallel, one fails and dumps the full load on the second causing it to short-out.then it blows the output fet and probably the zener across the fet.my fix is to fit a single 25A+ schottky diode in a TO220 package with a small heatsink on it inplace of the original diodes.
Uni-T UT139C - freezes after turning on - Page 1
Forum section: electronics / repair

author: Aborus
author_rank: Newbie
timestamp: February 16, 2018, 08:41:14 am
content: HiI need help with my UT139C. After 1,5 years it suddenly stopped work. Normally it beeps two times after turning on and then it's ready to use. But now it freezes after first beep. The buttons are kind of working, i can turn on backlight, and the symbols on lcd changes.When i turn on meter in calibration mode and then go to normal mode it can measure but only in DC.To clear things up i made a video illustrating problem:https://youtu.be/FATLlHZkn5EDo you have any idea if this can be repaired? Maybe reprogramming eeprom? Or do i stuck with paperweight?Any help would be appreciated

author: stj
author_rank: Super Contributor
timestamp: February 19, 2018, 08:32:29 am
content: try cleaning all the switch contacts.

author: daedalux
author_rank: Contributor
timestamp: February 21, 2018, 02:22:45 pm
content: Try disassembling it completely to the bare lcd, switch contacts, all clean, check fuses, broken solder joints and put new batteries on it.I have had this model for four years without issues.It's important if it failed after being dropped to the ground, overvoltage, overcurrent, or even high electromagnetic field as it has no contact voltage detection.

author: Aborus
author_rank: Newbie
timestamp: February 23, 2018, 04:30:08 pm
content: I cleaned all the contacts, fuses are ok, solder joints look fine too, i couldn't find any broken or bad joints. I tried changing batteries.It hasn't been dropped, overcurrented or sustained any damage. I used it only in low voltage applications. It was working fine, then sit for a month in desk, then i took it out and tried to turn it on and it wasn't working.

author: lordvader88
author_rank: Frequent Contributor
timestamp: February 23, 2018, 05:09:48 pm
content: Do u have another meter or oscilloscope to start poking around ?I have a FS9922-DMM4 based VC99, and it freezes and does weird things because the selector knob/contacts are doing something wrong and making extra contacts or not enough sometimes. I doubt I've done anything to damage it's chip, only working at breadboard stuff with 1-2A @12V if it all went bad.