hybridfree/eevblog-posts huggingface dataset:
Strange electrolytic capacitor failure,  - Page 1
Forum section: electronics / repair

author: CaptDon
author_rank: Super Contributor
timestamp: September 04, 2021, 12:59:47 pm
content: Just wanted to share this experience with you troubleshooters. We have a Carver PM-350stereo amplifier used as a monitor amplifier in our band. The left channel started to sounddistorted and while it was on my bench for repair it kept getting more distorted. I foundwhen I placed my finger on top of a TL072 the audio instantly cleared up. Checking forsolder voids and cracks and finding none I replaced the I.C. Seemingly and instant fix!!The unit was powered on and off several times and played for over an hour with no problems.Next morning the very same channel was out again!! Turns out this time, touch the I.C.and no joy, but touch the electrolytic beside the I.C. (470uf@6.3vdc) and presto, amp plays!!Bottom line, the cap was bad but in a strange way. What I found was when the amp wasturned off the capacitor would end up with about -1vdc on it and we know electrolytics hatereverse voltage. Apparently the negative voltage would cause the capacitor to developlow internal resistance when left to rest for 12 hours or more and then the amp wouldn'tplay when powered back up. Physically disturbing the capacitor would temporarily cure it!!!Drove me crazy trying to nail down why the amp was dead each morning and knowingit wasn't thermally related!! I replaced the cap with 470@16vdc to be more tolerant of thereverse voltage during the shutdown/bleedoff phase.

author: David Hess
author_rank: Super Contributor
timestamp: September 04, 2021, 03:44:23 pm
content: How old was the capacitor?That failure seems more like one lead of the capacitor was open inside. When they get old, the seal may leak allowing water in which corrodes the aluminum where it connects to the lead eventually causing an open.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 04, 2021, 04:38:48 pm
content: I just had to fix a high voltage power supply and one of the electrolytics failed in a similar way.The quick test of the cap showed it to be OK.They fail in many different ways.

author: bob91343
author_rank: Super Contributor
timestamp: September 04, 2021, 11:12:10 pm
content: The problem is that an electrolytic capacitor isn't a real capacitor. It's an electrolytic cell that just happens to have substantial capacitance. Devices like this have been causing trouble for decades. They have short shelf life and develop leakage for no obvious reason. Temperature is their enemy as well.Unfortunately there is nothing available to replace it. That's why people who work on old gear look at the capacitors first, and 'recap' has been a watchword. Of all the parts that can fail, it seems that capacitors are the worst. And there are many of them in most devices.
Strange monitor symptom - Page 1
Forum section: electronics / repair

author: james_s
author_rank: Super Contributor
timestamp: April 17, 2021, 06:34:08 am
content: I was brought this monitor to look at, it has an unusual symptom that I've never seen before and I'm curious if anyone has some insight into what's going on. Unfortunately when I uploaded the video to youtube it seems to have substantially reduced the quality but it still shows roughly what is happening. When first powered up or a signal is connected it looks great, no problems at all. Then after anywhere from 10 seconds to a few minutes, a wave of noise scrolls up from the bottom until the entire screen looks fuzzy and flickers, with some noise near the bottom that flashes periodically. Occasionally instead of scrolling all the way up the screen, a band will hover around the bottom varying in height from a few pixels to about half an inch. When it does act up I can unplug the video cable and plug it back in, or cycle the power and it will be fine again for a bit and then the strange effect comes back. Since it affects the onscreen menus too I suspected it was something between the controller and the glass and unrelated to the video input. This was confirmed by hot plugging the LVDS cable to the panel, doing that will restore a perfect picture again and then the problem comes back after a bit.So it seems that the fault is something in the panel itself, perhaps it's having an issue with the clock? I've never seen anything like it and it's kind of bugging me. It's too bad really, it has a great picture when it's working and it's an expensive touchscreen monitor.https://youtu.be/QmXGNh8PCjI
Strange Power Supply issue - Page 1
Forum section: electronics / repair

author: Megawilsound
author_rank: Contributor
timestamp: August 01, 2020, 04:47:38 pm
content: Hi allGot a strange one here.I have the power suply board for a Korg M1 synth, as it failed to power up the other day I removed it to follow Rule Nimber1 (The Shell Test Voltages).So I probe the out puts (5v DC and +12 -12) got zero.then out of curiosity I hoocked up the multimeter with thos little hook on things, conected the mains got zero so I unpluged the mains and the multimeter read voltages that droped quickly to zero.I have never seen this before.Wondering what could cause this, I have recaped the unit with brand new caps so dont think this would be causing it.Anyone else come across this before?Any help in finding the cause would be grate.ThankMegawilsound.

author: jmw
author_rank: Frequent Contributor
timestamp: August 01, 2020, 06:09:32 pm
content: Quote from: Megawilsound on August 01, 2020, 04:47:38 pmIf you connected the multimeter in DCV mode to the mains, which supply AC, you should expect to read zero.

author: Megawilsound
author_rank: Contributor
timestamp: August 01, 2020, 06:24:18 pm
content: Hi jmwI used a set of Probe Clips on the DC out puts I did not go near the Mains suply.If that makes sense.Mega

author: tunk
author_rank: Super Contributor
timestamp: August 01, 2020, 07:09:22 pm
content: I don't really have a clue, but I think for some SMPSs there's abootstrap circuit that should start the switching. It could be thatit's only starting to work when the voltage of the input smoothingcapacitor has declined to a lower level after you disconnected power.Again, it's just an uneducated guess.Edit: It may help if you post some photos.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: August 01, 2020, 07:31:15 pm
content: The rectified mains DC is connected directly to the transformer primary windings.On switch off, this DC must fall to zero, which presumably is inducing voltage spikes at the secondary.

author: Megawilsound
author_rank: Contributor
timestamp: August 02, 2020, 03:23:33 pm
content: Hi Allhere is a cuple of photos of the PCB I am in the prossess of repairing.It is the Powere suply for a Korg M1 synth bord version KLM-1269 220/240 AC Volt version.Todate I have removed and tested two components, an NEC transistor NEC C3531 89S and a Diode N9F 5K030, both tested faulty. I have found a new replasment for the C3531 however I am not having any luck in finding a replacment for the DIode. Any advuce on how to locate a replasment would be apreceated.Links to the photoshttps://drive.google.com/file/d/17bdm3b_ZaML5aMnFHbpzsvaCGL9l1bWK/view?usp=sharinghttps://drive.google.com/file/d/1uy2EFK7ZzdnuaNiZdKbsZfZ-ByCNLeBq/view?usp=sharinghttps://drive.google.com/file/d/1ppkeQKq0VPWzctWdNiEIR54iJqjpuXqB/view?usp=sharingThanksMega.
strange Quick 861dw problem - Page 1
Forum section: electronics / repair

author: VeryFastSnail
author_rank: Contributor
timestamp: December 15, 2019, 01:15:03 pm
content: Hello everyone. First of all let me apologize for this question, but I figured out that EE community might help...Long story short: I had this accident with my quick 861dw hot air soldering station, I was powering it down while it was ramping up the air pump , and after next power up it started, but it took 6-7 seconds more, buttons are responsive but I have to hold them longer and the whole air station works slower (maybe half as slow as normally), I mean every function, including powering up, to controlling heat and air speed, buttons matrix and other functions. even beeper that beeps when it boots, beeps for longer. How could I fix this problem? P.S station works as intended, but everything is so slow, its like delay(250) function was placed in loop()... PCB look perfect, no damage or nothing, MCU itself look fine. No caps are shorted around it.MCU atmega16AHave direct access to SPI via connector, but I can't connect to it either 0x0000000 err is dropped or 0xfffffffWhat I have already thought of:Replace MCU (where to get firmware, maybe extract it from current one while it still alive)Maybe there is issue with chip clock? Atmega runs on 16 mhz right? Maybe there is any way that it got slower? maybe 8mhz? that would explain slower performance..Extract firmware somehow from it... There is connection of 7 pins on the board that is connected to MOSI MISO SCK AND RESET, then two pins for +5v and gnd, but I wonder if that chip is locked... if not replace mcu and flash old firmware.I saw zener diode that has very low resistance across it 2ohms, but it's connected to temperature sensor or something so maybe its normal? :?there are external oscillator place, but internal fuses needs to be programmed...Maybe there is external pin of clock that I could sample with my oscilloscopeWhat do you think?
Strange SMD component - Page 1
Forum section: electronics / repair

author: sokot13
author_rank: Newbie
timestamp: August 03, 2024, 10:27:10 pm
content: Hello !I encountered this strange component on a PCB. Its package is cylindrical and it has four terminal forming a "cross". Its label is prefixed by "U" and two of its terminals are grounded. The only marking is a "3".Do you have any idea what it can be?Thanks!

author: Kurets
author_rank: Regular Contributor
timestamp: August 03, 2024, 10:33:27 pm
content: U indicates an IC. The footprint and pinout is typical of RF transistors or amplifiers. So very likely it is an IC RF amplifier of some sort, LNA or PA (low power)

author: sokot13
author_rank: Newbie
timestamp: August 03, 2024, 11:00:18 pm
content: Thanks for the tip! This is probably a Mini-Circuits ERA-3SM.

author: fzabkar
author_rank: Super Contributor
timestamp: August 03, 2024, 11:22:01 pm
content: https://www.rcscomponents.kiev.ua/product/era-3_71820.html
Strix connector for kettle? Burned? - Page 1
Forum section: electronics / repair

author: analogo
author_rank: Regular Contributor
timestamp: November 07, 2019, 07:20:42 pm
content: Hi, a short circuit in my the base kettle made the circuit breaker of my apartment go pop. Upon inspection I realized that the base contains just a Strix centre connector. The AC wires are directly connected to its input. No fuses, no nothing.What is weird is that there is some kind of powder at the base of the connector and on the spades, see photo.What could this greenish powder be?Limescale? How did it get there?BTW, do you knowwhere can I buy a new Strix connector for the base?

author: oPossum
author_rank: Super Contributor
timestamp: November 07, 2019, 07:29:48 pm
content: Quote from: analogo on November 07, 2019, 07:20:42 pmOxidized copper.
Stroke sensor on rowing machine not working. - Page 1
Forum section: electronics / repair

author: Dpfenny
author_rank: Newbie
timestamp: February 03, 2022, 11:08:50 pm
content: The sensor attached to the wheel on my rower is not registering strokes. I took the cover off and noticed one of the two “sensors” was loose. They were basically hot glued into place. After adjusting on the loose one for a few minutes I finally got it to register strokes. I rowed for a few minutes and every thing worked fine. I grabbed the hot glue gun and plugged it in. While I waited for it to heat up, I decided to remove some of the excess hot glue that was hanging there. I went to test it again before I applied the hot glue and it would not register the strokes. I am not sure what else to try and am unsure where to even find a replacement part. The manufacturer was of no help. I attached a pic of the sensors in place and another of the sensor that was loose. Part of the plastic is broken off.

author: fzabkar
author_rank: Super Contributor
timestamp: February 04, 2022, 12:13:39 am
content: I can't make much of the photos, but could the sensors be reed switches, and are there magnets on the wheel? The reed switches should click when a magnet is placed in proximity.

author: Dpfenny
author_rank: Newbie
timestamp: February 04, 2022, 06:08:54 am
content: I think these pics might help. The wheel has three contact points. The wires are connected to tje piece I adjusted as well as one right next to it. Thanks for taking a look at it.

author: fzabkar
author_rank: Super Contributor
timestamp: February 04, 2022, 06:16:51 am
content: It should be easy to confirm whether the three "contact points" are magnets. The reed switches can be tested on the resistance range of a multimeter. The resistance would be either 0 or infinite.Here is something similar:https://www.ebay.com.au/itm/254010855539I guess that the reason for two sensors is so that the microcontroller knows which direction the wheel is turning.
Strong 207b speed control - Page 1
Forum section: electronics / repair

author: hit180
author_rank: Newbie
timestamp: November 10, 2024, 09:38:19 pm
content: Hello,I have some issue with Strong 207b nail drill control box, the motor works in a maximum speed and speed controldoes not work. Does anyone see this problem?

author: fzabkar
author_rank: Super Contributor
timestamp: November 10, 2024, 10:16:34 pm
content: Perhaps there is a shorted TRIAC?
Stuck yet again on a SMT part.....help!!! - Page 1
Forum section: electronics / repair

author: rfengg
author_rank: Regular Contributor
timestamp: December 27, 2024, 03:52:01 pm
content: Hi all,Need your help on what the part number of attached pic could be? The marking reads to me as ANW.There is another exact part on the same PCB and it measures as a NPN BJT.....for the life of me, I cannot find a BJT marked as ANW.Most of the BJT SOT23's, I am familiar with, have the right pin as the Emitter, but on the working one, it shows up as the Base.Trust you guys to get me out of this one........

author: inse
author_rank: Super Contributor
timestamp: December 27, 2024, 04:02:10 pm
content: Is there silk screen that says it’s a transistor?Could also be a double diode…Edit: I found MAX810 viahttps://www.google.com/search?q=sot23+ANW&ie=UTF-8&oe=UTF-8&hl=de-de&client=safari

author: rfengg
author_rank: Regular Contributor
timestamp: December 27, 2024, 04:04:23 pm
content: Ah, yes.....the silkscreen says its Q12.....other dual diodes are indeed marked with a "D" prefix.

author: shapirus
author_rank: Super Contributor
timestamp: December 27, 2024, 04:10:25 pm
content: It may be a linear voltage regulator. I think it requires a bit of research of the surroundings.

author: inse
author_rank: Super Contributor
timestamp: December 27, 2024, 04:13:26 pm
content: Unlikely, “Q“ is strong evidence for a transistor

author: rfengg
author_rank: Regular Contributor
timestamp: December 27, 2024, 04:20:14 pm
content: Also the other Q's with the same part number, read on a DMM, as a BJT.

author: shapirus
author_rank: Super Contributor
timestamp: December 27, 2024, 04:20:22 pm
content: Quote from: inse on December 27, 2024, 04:13:26 pmah yes. my bad, missed that and/or confused with "U".still, would make sense to investigate the surroundings. might be a generic part, but then at least it has to be determined if it's a fet or bjt.

author: fzabkar
author_rank: Super Contributor
timestamp: December 27, 2024, 08:10:11 pm
content: BSS138P, NXP, 60 V, 360 mA N-channel Trench MOSFET, marking AN*, SOT23:https://www.aliexpress.com/w/wholesale-anw-sot23.htmlhttps://assets.nexperia.com/documents/data-sheet/BSS138P.pdf

author: rfengg
author_rank: Regular Contributor
timestamp: December 27, 2024, 08:42:44 pm
content: @fzabkar .....you could be right....what is confusing the hell out of me is that another exact part on the same PCB, measures as a NPN BJTTime to hot air it off I guess, and put it on a component tester as I was making in-situ measurements.
Studio Monitor Repair Volume goes up and down automatically - Page 1
Forum section: electronics / repair

author: apro
author_rank: Newbie
timestamp: August 13, 2019, 08:37:32 pm
content: I have a MAudio DSM 3 studio where the volume started automatically going up and down since last week. I opened up the system and had a look.All the capacitors look alright. havent tested them yet. Thinking of cleaning the volume pot. Any ideas how I should trouble shoot.Moreover I have seen an youtube video of someone replacing the J13007-2 transitors for a different issue, in the same speakers. Wondering if that makes sense in this situation?Is there a way to test the transistors in circuit, like i can test capacitors using ESR. Many thanks for your help.
Sub for MFE-3002, MFE3002 - Page 1
Forum section: electronics / repair

author: cncjerry
author_rank: Unknown
timestamp: January 11, 2017, 03:41:23 am
content: Last week when I picked up the Fluke 332D I also brought home a Dial A Source 46A. This is another voltage standard having a pretty decent KV divider and two ranges, +/-10 and +/-1.The unit was working well, seemed stable after being left on as recommended, until I noticed the output was sitting at -14 instead of +10. In tracing through the schematic, I isolated the problem to the output/sense amplifier referred to as a CSA. It is meant to be replaced and no discrete schematic is provided. I've since sent a note to the parent company as they still sell a follow-on model.I checked all the diodes, caps and transistors. The +15 was low and I didn't realize until later that there was a bad cap in the power supply. I'm starting to think that might have cause the chain of events that took out the CSA board. The board also has two LM308H op amps which I didn't check and two MOSFETs, MFE3002 type. As near as I can tell they are general purpose low voltage amps/switches. There is clearly a big difference between the two MOSFETS while doing a simple diode and resistance check and consequently, of course, the most unobtainable part is the one that seems to be failing.Looking online I found a place in the UK that claims to have them and I sent them a note.Optimistically, I am posting here to see if anyone knows anything about them and if so, can recommend a common sub? They are listed simply as a 20V N-Channel switch. By the way, they are 4-leggers in a can.For those that like pictures, here's the DAS-46A, MOSFETS and CSA board. I'll be cleaning the board when reassembled. Also, I have the sense and output links open for debugging.Thanks

author: KhronX
author_rank: Frequent Contributor
timestamp: January 12, 2017, 09:59:10 am
content: Some quick googling revealed this:http://www.ersinelektronik.com/class/INNOVAEditor/assets/Datasheets/MFE3002.pdfSeems like they are indeed some pretty standard-ish low-voltage MOSFETs.Regarding the TO-72 package, this document has several pinout variants:https://www.centralsemi.com/PDFs/case/TO-72PD.pdfPin 4 always seems to be connected to the case, apparently - that should be easy enough to check, though

author: r6502
author_rank: Regular Contributor
timestamp: April 11, 2021, 01:45:48 pm
content: Hello cncjerry,I also own a DAS, but a different model. Mine is the DSA 56a, and has also a CSA build in, that is currently nor working. It could also be addressed to the MOSFETs but I'm not sure. Dit you get your model back working?I took a look on your CAS that looks similar to mine, so I think, GR puts the same CSA in different models.I have also drawn a schematic of the CSA. You can find it here:https://www.eevblog.com/forum/metrology/general-resistance-das56a/25/Guido
Substitute for OPA2170 - Page 1
Forum section: electronics / repair

author: jerryk
author_rank: Regular Contributor
timestamp: December 01, 2022, 08:19:38 pm
content: I am trying to find an acceptable substitute for theOPA2170 dual opamp in a SOIC 8 package. The OPA2170 is not available or is at a price that is ridiculous as in over $10.00 US. I looked on mouser and have come up with theTLV2170IDRas a possibility.The opamps are used the attached circuit. I'm not familiar enough with the specs to know for sure and appreciate any suggestions.Jerry

author: fzabkar
author_rank: Super Contributor
timestamp: December 01, 2022, 08:34:45 pm
content: It seems that your proposed substitute is a good fit. My concern is that both devices are rated for 36V operation, which is just marginally higher than the supply voltage of your circuit. Not much head room ...All the op-amps are configured as voltage followers. AFAICT, the most important requirement would be a high input impedance so as not to load the current in the string of resistors (~3mA).One concern in both cases would be the V8 voltage. Both op-amps are only guaranteed for linear operation when the inputs are below Vcc - 2V. That's at the limit of the circuit.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 01, 2022, 08:36:12 pm
content: The TLV2170 is the low cost version of the OPA2170 - essentially the same chip, but lower grade/less tested.The circuit used the OPs as buffers for some reasonable low impedance signals. The effort with fine trim suggest that precision may matter, but the trimmers could also compensate for offsets. For most of them an OPA2202 should be OK, for the 2 at the extremes the common mode range may be an issue, need to check.The OPA2202 is much better precision, but slightly higher input bias and higher supply current.If const is an issue and the trimmers would be used to compensate offsets, I would consider MC33172/MC34172 - the highest votlage may not work though, at least a close call to be checked.
Bump: Substitute line filter for HP54201A - Page 1
Forum section: electronics / repair

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: December 20, 2023, 01:14:42 pm
content: Any suggestions for a suitable replacement line filter?Trying to find a replacement line filter suitable for an HP54201A oscilloscope. Was getting it ready for disposal - figured it might be a useful first scope for someone starting out. It's been in storage for over a year. Booted up and self-calibrated OK but after about 15 minutes it blew lots of magic smoke. However, it continued working till I cut power and is seemingly still functional. Turned out the Schaffner line filter has let go. Easy clean-up and no evident harm to PCB. Perhaps I should have brought it up to operating voltage more slowly with a variac?Can't find any spec sheet or details for the fitted FS 2150-6-07 apart from schematic and specs on the housing (photo attached) or anything in the FS series. Can anyone suggest a suitable replacement? I had a look at the current Schaffner range but couldn't confidently work out the right substitute. Perhaps an FN9233 series would suit (https://www.schaffner.com/product/fn9233)?

author: Haenk
author_rank: Super Contributor
timestamp: December 20, 2023, 03:07:57 pm
content: You did nothing wrong, even ramping up the voltage would have blown it up.Post mortem fun: 5 bucks on "blown RIFA cap inside"

author: Stray Electron
author_rank: Super Contributor
timestamp: December 20, 2023, 07:14:49 pm
content: FYI another thread on the same model scopehttps://www.eevblog.com/forum/chat/hp-54201a-digitizing-scope-worth-buying/My first DSO was a HP 54501A. I still have it, it still works and I still use it on occasion. Great scopes IMO.
Subwoofer Amp gone very quiet - Page 1
Forum section: electronics / repair

author: 7AudioBB
author_rank: Contributor
timestamp: April 03, 2025, 07:03:09 pm
content: I've got aQ Acoustics 3070sactive sub and it suddenly got really quiet. I checked the power supply and it has +27, 0, -27 DC volts on it's output so that seems fine. The amp board has the LED on and the level and LF cut-off knobs work but they probably adjust the input only. It seems like the two 4 ohm speakers are powered only by the line input as they are really quiet with no visible cone movement, although the sound is not distorted.I checked the conventional larger electrolytic caps, they measured fine in circuit and reflowed the legs of the switches, but that didn't help. It's got aTDA8920CTHamp chip which gets too hot to the touch even after seconds with no input which is strange fore a high efficiency class D amp. If anyone got experience with this kind of problem I'd like to get some suggestions how to diagnose the chip or what else to look at, what could be the cause.

author: 7AudioBB
author_rank: Contributor
timestamp: April 03, 2025, 07:22:09 pm
content: It looks like one of the medium caps (C101) is already a replacement. The board is quite dirty as well which might be flux residue.

author: u666sa
author_rank: Frequent Contributor
timestamp: April 03, 2025, 07:53:38 pm
content: What you do is inject a sine wave on the input and follow it with oscilloscope.

author: MathWizard
author_rank: Super Contributor
timestamp: April 06, 2025, 06:14:36 pm
content: Or even with a good DMM on AC, the output of the op-amp sections could be a few volts AC with the volume cranked. Even touching your finger to the input should couple some mains AC noise like 60Hz or whatever. If you had nothing else, you can make an audio frequency 2 BJT oscillator too, with a few resistors and a cap or 2. Or 555 timer circuit, etc. And of course these days everyone has an MP3 player or something.IDK about that TDA8920CTH without it's heatsink on, but yeah getting too hot to touch sounds like it's cooked, but IDK, maybe they just run hot ? It says the idle current is around 75mA rail to rail, and so if it's running off the +/-27V, thats about 4W, so yeah that could could get pretty hot, wow a cigarette cherry is around that level.I'd want to know the current draw, of the various rails, if I suspected a dead chip. Normally if it was really short, it would pull down the voltage rails, but depending on the short, and the PSU, you might not notice. I have a nice bench PSU with current limiting, so I'd hook up to the rails and see directly how much juice it they were using. Depending on the repair, I might power only certain sections of a PCB, even if it meant cutting traces or removing resistors or links, etc. Or remove an IC to see if the problem clears.
Subwoofer amplifier no signal out of input board - Page 1
Forum section: electronics / repair

author: Fried Chicken
author_rank: Regular Contributor
timestamp: March 21, 2024, 05:14:31 pm
content: I have an Allison AL10 which is a fantastic subwoofer, mated to terrible electronics. Unfortunately the terrible electronics are now rearing their terrible head and the thing isn't working right.I already replaced every capacitor on the board, and then I started poking around with the oscilloscope. The signal seems to die somewhere on the input board, the amplifier side seems to work.I hate to do this, but I've made a thread on anaudio forumdescribing what I've done/looked at so far.I can't find the schematics anywhere.I'm currently suspicious of the Zener diodes, but if they've failed, idk how to replace them w/o schematics or part #'s. I can't test them if they've failed, and I can't decipher any numbers on them either.Maybe the best option is to buy a different higher quality plate amplifier.I tried to attach images in a neatly organized fashion but wasn't able to. Images of the input board, amplifier board, vertical section of the amplifier board, and a # from the PCB attached

author: Audiorepair
author_rank: Frequent Contributor
timestamp: March 21, 2024, 06:33:59 pm
content: Look at all the small black transistors (Q1, Q2 etc) to see if any are JFETs.These are usually marked J*** and are often used as the muting transistor(s).You might get lucky and find one, and it is faulty, so the pre-amp is permanently muted.For some reason these mute Jfets seem to fail more often than most other components.

author: Fried Chicken
author_rank: Regular Contributor
timestamp: March 21, 2024, 08:18:38 pm
content: I'll give it a look. There is a bypass option on the input for auto standby, which I would expect would bypass any muting circuitry

author: Audiorepair
author_rank: Frequent Contributor
timestamp: March 21, 2024, 09:53:44 pm
content: Mute Fets have a habit of failing short, thus permanently shorting whatever signal they are meant to mute.There is no way to bypass that.You can just cut them off the board to get the thing working.

author: Fried Chicken
author_rank: Regular Contributor
timestamp: March 21, 2024, 11:11:08 pm
content: When I checked the signal I didn't see anything. What sort of signal should I see?I can of course just pull the fets and test them
Successful repair of Samsung Washing Machine front panel buttons - Page 1
Forum section: electronics / repair

author: Chalcogenide
author_rank: Regular Contributor
timestamp: August 14, 2025, 09:07:38 am
content: Just a quick story of a successful and cheap repair of a Samsung washing machine model WF71F5E2W2W, but more specifically of the "front panel board" marked DC92-01237 on a sticker and DC41-00204B on the PCB. The PCB itself is likely used in a bunch of Samsung Washing Machines as it has a myriad of assembly variants and option diodes so maybe this will help somebody else. Attached is a picture of the board markings and the two switches that are the culprits of the failure.SYMPTOMS:The button to start and pause the wash cycle had become super-unreliable, sometimes requiring a good minute or two of wiggling before it registered a button press.SOLUTION:Replace said button (a tactile switch on the PCB) as contact cleaner failed to improve the situation.PROBLEM:No schematic available (obviously) and no source (that I could find) of replacement tactile switches for the specific board.SOLUTION - HUNTING:I started hunting around with the photo of the switch and the measurements, as no manufacturer marking was discernible on the switch itself.Eventually I found a suitable replacement on LCSC - part Khon TSX08131-130B334BA-L1000https://www.lcsc.com/product-detail/C42435386.htmlwhich also happens to be wonderfully cheap.The new part is not an exact match, as the original switch had a shorter "body" and longer "stem" compared to the replacement, but the overall height is the same and the lead spacing is the same, so they fit and operate just fine. Replacement is very easy as they are through hole parts with two leads.I hope this quick post will be helpful for anyone attempting a similar repair.
Successfull "repair" of a Owon SDS7102 - or is there still a problem? - Page 1
Forum section: electronics / repair

author: mifritscher
author_rank: Newbie
timestamp: January 07, 2022, 08:47:48 am
content: My Owon SDS 7102 was completely dead when switching on yesterday - both on AC and with the integrated battery. After a short investigation, I found that the battery didn't delivery any voltage, and the device uses only the two outmost pins of the battery pack. I could charge the battery externally - the beginning voltage of a bit over 6 volts confirmed that the battery was empty. After charging it with 6 Ah (the designed capacity was 8 Ah, and I played safe here) I but it back into the device - and it worked again! Both via only battery and with battery+AC. In the later case the led is orange (normal for charging), and the fan is a very tiny bit louder, so also the AC part seems to be fine.Or should I suspect a further problem?
suggestions for connecting to pogo pins - Page 1
Forum section: electronics / repair

author: retiredfeline
author_rank: Frequent Contributor
timestamp: January 11, 2021, 05:30:39 am
content: I have a working keepsake from a Toshiba cassette walkman I owned back in the early 80s. It's a cassette that contains a FM tuner, turning the walkman into a radio. As you can see from the photo of the back, it has pogo pins that mate with a connector under the cassette compartment and the walkman can be switched to power the tuner and take the audio signal from there. You can see I labelled the pin functions before the walkman was recycled.I would like to connect this "cassette" to a power supply and my entertainment amplifier as a retro accessory. I would also need to connect an antenna wire; this was provided by the headphones in the original.Q: Any suggestions how I could connect to the pogo pins securely without much ugliness at the front? Sorry I don't have a 3D printer to make a cradle for the "cassette". In fact I hope to put it on a fold-out acrylic easel.

author: Nusa
author_rank: Super Contributor
timestamp: January 11, 2021, 06:36:48 am
content: Take some proto-board with plated-through holes, cut to size to match the side of the cassette. Drill/file out some registration notches to match the plastic protrusions next to the pogo pins. Determine which plated-through holes match up to the pins and attach wires to the protoboard for each signal. Cover with some electrical tape and clip it on with spring clips of some sort. And of course bundle your wires into a harness and connect them to your amplifier/antenna. Plenty of ways to improve on that, but quick and dirty should work.That lock switch looks interesting. If you figure out how that works, you might be able to rig something to engage that instead of using a clip.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: January 11, 2021, 06:53:45 am
content: Thanks. The lock switch simply held the cassette in place in the walkman compartment. It slid out a metal tab.
SUGON 3005D 30V 5A DC Power Supply faulty - Page 1
Forum section: electronics / repair

author: jaaa1976
author_rank: Contributor
timestamp: November 13, 2021, 01:08:07 pm
content: Hi..please help me repair SUGON 3005D 30V 5A DC Power Supply .It give output 53 volts always now..i found damaged resistor in picture..if i desolder wire where resistor was it give same 52.5 volts and show 5AMP on front power supply.It looks similar board in new KORAD 3005D. Which part can you suggest replace first? i already use R100 resistor and not help..same voltage 53 volts.Thanks

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 13, 2021, 02:34:39 pm
content: randomly replacing parts is not the way to go. since you have the full unregulated DC voltage on the output, my guess is that the series transistor got fried; the burned resistor is just a by-problemmy guess too is that it is a Korad-like PSU, so you should find quite a bunch of references here in the forum.for the very first I'd check the transistors

author: jaaa1976
author_rank: Contributor
timestamp: November 13, 2021, 02:49:25 pm
content: Quote from: HB9EVI on November 13, 2021, 02:34:39 pmHi..do you mean d1047 transistors in picture ? i will buy and replace then..thanks

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 13, 2021, 02:55:35 pm
content: well my glass ball is actually in service, so you'll have to measure. you're not going to replace parts just by a gut feeling but by measured facts

author: jaaa1976
author_rank: Contributor
timestamp: November 13, 2021, 09:29:37 pm
content: Quote from: HB9EVI on November 13, 2021, 02:55:35 pmOK..psu working now ..d1047 transistor was shorted .. I have home d718a transistor from audio receiver ..replaced and all good now.. will replace later with d1047 transistor when i will receive by post...thank you for help.
Sun Blizzard A/C Machine QTech II - troubleshooting board and cpu - Page 1
Forum section: electronics / repair

author: DK87
author_rank: Newbie
timestamp: May 02, 2019, 02:43:26 pm
content: Hi there,a few days ago I obtained an A/C servicing machine for cars/trucks.It's in rather nice condition, but has one major issue: the LCD isn't showing anything. (see attachment)So I began to remove the board along with the lcd to test it on the bench.I took an visual inspection and I found an corroded ic (but seems to work just fine...I had probed it later)Then I probed the connections comming out of the board to the LCD and there is no valid signal comming out of it:frameground, ground, backlight positive and backlight ground are workingpin 6 (Read Select :->5V 140Khz square wave signal.... seems to be okay?pin 11 (DATABUS 0) -> 3V 70 Khz sqare wave signal hmm...All other lines are DEADSo I think the problem is not the LCD.I digged further and tried to get a connection to the LPC2148, but nothing works.I probed UART0 Pins of cpu ->no valid signalI probed UART1 Pins of cpu ->no valid signalI tried usb-connection: error, windows says the device doesn't work.Even if I pull the RESET pin low, and pin 0.14, so that the cpu will start the bootloader..no connectionsI checked power supplies: 12V ok, 5V ok, 3.3 V ok.I suspect the cpu hangs, has corrupted user software or is just faulty.So, can you help me further?Do I have missed something?Btw I noticed:There are HCT573 octale D-Type latches.On a few latches the LE (LatchEnable) pin is on the 5V rail. Why?I thought especially the latches which are connected to the lcd take the LE signal to send the databits simultaneouslyto to the lcd?Unfortunately, I have no service manual or anything about that machine.I contacted the manufacturer SUN aka Snap-On but still no answer.Detailed and annotated pictures of the pcb are on my onedrive accout:https://1drv.ms/f/s!AjDFITipILdAyUSNivWeN7ldm3ejThank you!

author: Turhabi
author_rank: Newbie
timestamp: August 12, 2022, 07:06:23 am
content: Hallo mein Freund ich habe gleiche Fehler wie bei die mit meinem klimagerät kannst du mir helfen hast du repariert was war den fehler bitte um Rückmeldung?Liebe Grüße

author: ebastler
author_rank: Super Contributor
timestamp: August 13, 2022, 03:43:03 pm
content: DK87, the original poster, has last been seen on this forum in 2019. (You can click his user name in the post above to see that.) So it is unlikely that he will respond. Also, please note that this forum uses English language.
Sunkko 737G spot welder - Page 1
Forum section: electronics / repair

author: hpmaxim
author_rank: Regular Contributor
timestamp: June 23, 2023, 05:30:07 am
content: I have a Sunkko 737G which has always worked fine for me. A few days ago, I turned it on, and it worked fine. I turned it off, and then turned it back on about 15 minutes later -- and the fuse in the back blew immediately as I flipped the on-switch. It appears to use a glass 30A fast-blow 5*20mm fuse. I didn't have any but a coworker gave me a 20A fast-blow ceramic fuse. I tried the 20A fuse, and it seemed to last 2-3 seconds before blowing (I think it took a lot longer to blow than the original 30A fuse). It seems there is a legitimately large in-rush current.I see a couple scenarios here:1) There's some legitimate problem with the welder. I opened it but didn't see any obvious scorch tell tale scorch marks (there was someone else on here, RustyCaliper) who had a component blow up right before his fuse blew. But I don't see clear evidence of that.2) The original fuse blew because the large inrush currents eventually wore the fuse out to the point that it blew. The 20A fuse I replaced it with just wasn't enough because, it legitimately needed a 30A fuse. This seems like a poor design to me (that's very little margin on the fuse, and the inrush current is wearing out the fuse?) and I'm wondering if I want a slow-blow fuse, perhaps with a smaller amperage. Ultimately, the line is on a 15 or 20 amp breaker which obviously takes longer to trip than a fast blow fuse -- making me wonder what the point of a 30A fuse is that protects against extremely high inrush currents, but also false blows after a while.

author: hpmaxim
author_rank: Regular Contributor
timestamp: June 27, 2023, 03:26:13 am
content: Replaced the fuse with a 30A ceramic and this time the circuit breaker tripped, so there's something wrong with the machine, the problem isn't the fuse. I didn't see any clear damage to any component, although D3 looked like it might be a bit buggered. Does anyone know these machines enough to aid me in diagnosing the problem?

author: ferrisd65
author_rank: Newbie
timestamp: July 09, 2023, 11:01:35 am
content: https://youtu.be/JDIOp8QbHWQ

author: marhuum
author_rank: Contributor
timestamp: July 10, 2023, 12:19:21 pm
content: put its schematicdo google: 'list of electronic. component which will get short when it's faulty'likely here; hi-power Mosfet(s)that's in primary T, because this kind device should principally just hi ampere SMPS
Sunn Concert Bass Amp - Troubleshoot and Repair - Page 1
Forum section: electronics / repair

author: jcrubin
author_rank: Frequent Contributor
timestamp: July 29, 2019, 12:38:10 pm
content: It's not often I work on transistorized amplifiers, however a couple of times a year I take on such a project. This Sunn concert, built around 1973 was owned by the same person since around that time and was looking for electronic repairs with no cosmetic work. I decided to take on the task.The complaint was noise in the system, though, i did not attempt to turn it on without first a visual inspection. With that, seeing the state of the capacitors and the fact that the main board was floating, having lost all of the mounts over time, id decided that some repairs would first be required before a smoke test. The broken mounts were further enough to pull all of the resistors from their heat sinks as well over time.The some capacitors were strange sizes, and by strange i mean costly, a few were checked for leak-down and ESR, the rest were replaced wholesale. all sized needed to be reverified because someone had been in here before. Special consideration was given to the main filter caps, given their cost, though, they tested good enough for now.Swapping the caps from the main board also meant cleaning the board with spirits to remove all of the old electrolyte. The pads are delicate on this amp and care should be taken to remove and add components. Once the main board was finished, new nylon stand-offs were added, the board holes slightly reamed to M4 and the board remounted. Subsequently, the resistors were placed back into the heat-sink clips. A smoke-test confirmed the amp works but artifacts are in the system, Im reserving judgment until the pre-amp is completed.The next task, the pre-amp board, was removed also to swap capacitors and apply Deoxit the pots. After reassembly, the artifacts persisted. The first hint as to the problem was the fact that the artifact noise became attenuated with the volume; this put the issue behind Q103. Localizing the issue to two components with the o-scope I broke out the signal tracer to isolate the noise generation to the .01uf coupling capacitor off of Q102. Confirming this in noise mode, it was swapped out and retested. The problem was solved and final testing of the amp conducted.Having been proven out the amp is reassembled.
sunny boy  sb 2500  - Page 1
Forum section: electronics / repair

author: bessem2fr
author_rank: Newbie
timestamp: June 02, 2019, 11:55:45 pm
content: my sma sb 2500 is no more working ... i need a photo of electronic unit ...

author: bessem2fr
author_rank: Newbie
timestamp: June 03, 2019, 09:30:50 am
content: voila le composant que me manque .. une photo de la carte va m aider a le trouver

author: voltampere
author_rank: Regular Contributor
timestamp: June 07, 2019, 06:52:02 am
content: I have a SB2500 fully disassembled here. It broke down and i replaced it with a new model.Which picture do you need?What is broken?RegardsJoerg
Sunny boy sma - Page 1
Forum section: electronics / repair

author: denis.b
author_rank: Newbie
timestamp: February 04, 2021, 10:09:01 pm
content: Sto riparando un sunny boy 5000 che non si accende.Ho trovato il componente difettoso con la freccia rossa sul file immagine allegato.Qualcuno gentilmente può indicarmi la sigla del componente?Qualcuno ha disponibile lo schema elettronico anche solo di quella parte di circuito?Ringrazio da subito chi mi vorrà aiutare!

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: February 04, 2021, 11:12:16 pm
content: Penso sia un regolatore di tensione. TLE4274 per essempio.Misurare la tensione su tutti i pin p.f.I think that's a voltage regulator. TLE4272 for example. Measure the voltages on all the pins please.

author: denis.b
author_rank: Newbie
timestamp: February 05, 2021, 12:12:20 pm
content: Penso sia il circuito di accensione dell'inverter quando la tensione DC dei pannelli arriva in soglia.Ho scritto sull'immagine allegata le tensioni.Con 350V in ingresso si è sempre acceso ed ora non più.Ho provato tramite alimentazione esterna ad alzare i 5V e quando arriva ad 8V l'inverte si accende bene.Probabilmente il componente con freccia rossa è in perdita.Potete aiutarmi a capire che componente possa essere?Grazie

author: denis.b
author_rank: Newbie
timestamp: February 05, 2021, 12:20:12 pm
content: Sul componente c'è scritto: 053

author: denis.b
author_rank: Newbie
timestamp: February 05, 2021, 05:34:02 pm
content: Scusatemi ho letto capovolto.Il codice del componente è E50

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: February 06, 2021, 12:47:03 am
content: Davvero non lo so. Mai visto un componente "E50". Ti consiglio di cercare presso i distributori e controllare tutti i convertitori nel pacchetto TO252-3. (mouser, digikey, puoi filtrare per pacchetto). Oppure contattare il produttore tedesco per un manuale di servizio.Mi dispiace!
Super I/O datasheet IT8726F ? - Page 1
Forum section: electronics / repair

author: PKTKS
author_rank: Super Contributor
timestamp: March 16, 2020, 12:55:11 pm
content: Strangely enough I have more than dozen ITE it87xx datasheetsBut by no means I can find the one I need now...Anyone with some clue WTF is wrong with ITE IT8726F datasheet ?Nowhere I can find not even a reference for it...May be someone knows if it fits other IT872x layout specs ?ThankxPaul

author: PKTKS
author_rank: Super Contributor
timestamp: March 16, 2020, 01:02:05 pm
content: Thanks for your attentionMy browser is not capable to "display" those characters properlyIt "looks like" a pdf reference is available but I can not parse that thingwith those characters...If you can attach or reroute that would help.I have a MOBO with that and I need the full Vcc VTT and Vsbpins numbers to check...Paul

author: PKTKS
author_rank: Super Contributor
timestamp: March 16, 2020, 01:09:43 pm
content: Thanks a lotGood enough for my purposes..Paul

author: PKTKS
author_rank: Super Contributor
timestamp: March 16, 2020, 01:34:46 pm
content: Quote from: blueskull on March 16, 2020, 01:08:09 pmBig thanks again.. the attach rerouted me to this MOBO schematicwhich I managed to get just fine..Great
Support detect error Fluke 5500A - Page 1
Forum section: electronics / repair

author: phucneo
author_rank: Newbie
timestamp: July 11, 2023, 03:08:25 am
content: Hi everybody,i need help,I have auctioned 1 fluke 5500a, when I received it, there was an error,it doesn't seem to be connected to the A9 cpu,Has anyone encountered this error,I'm waiting for the auction company to handle it so I can't teardown it yetdetail error i attach picture bellow, thank for all

author: Ugur
author_rank: Regular Contributor
timestamp: July 11, 2023, 05:33:02 am
content: There may be a bad contact in the sockets. Maybe it was experienced during transportation.Removing the cover and removing and reinstalling the cards may fix the problem.

author: phucneo
author_rank: Newbie
timestamp: July 11, 2023, 04:20:22 pm
content: Hello, i try install all card, but it same condition, are you have other handling?

author: seebeck
author_rank: Contributor
timestamp: July 12, 2023, 03:39:10 pm
content: Changes background and contrast settings for the LCD display, I guess that could help.Or attempt to measure waveform for Digital Pins of the LCD to judge the status of A9 CPU board is better.For A9 CPU board and FW2.61, please refer to:https://www.eevblog.com/forum/repair/fluke-5500a-repair-attempt/

author: Halcyon
author_rank: Unknown
timestamp: July 13, 2023, 08:08:34 am
content: Locked duplicate thread.
Support Repair N9320B, Amplitude Level measuaring is incorrect - Page 1
Forum section: electronics / repair

author: Thuyvv
author_rank: Newbie
timestamp: March 30, 2022, 06:46:32 am
content: Hi All,I have an errored unit N9320B, the Amplitude Level measuring is incorrect, the result measuring is larger than the RF level at the input ~ +6 ÷ +7 dB,The monitor display ERROR 102. 50 MHz calibration reference unleveled when I Align allPlease see the video in this link and help us fix this error,https://youtu.be/LjFS4vwu_VEThanks!