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#73 - Mackie Thump TH-12A bad woofer
This Mackie Thump speaker has a damaged woofer with a shorted voice coil. The symptom was demonstrated, and the diagnosis was confirmed by measuring the voice coil both at DC and at 1KHz. A good woofer was also measured (not the same model) to show the difference.
Previous Mackie Thump TH-12A repair: https://youtu.be/5zkEzjyKNjg
#72 - Fluke A90 current shunt
This is a look inside of a vintage piece of metrology gear by Fluke. The unit is, probably, more than 40 years old, and seems to be in spec.
#71 - Zoom R16 repair
This R16 had a bad SD Card connector. It turned out to have a bent pin, that broke off in an attempt to straighten it out. The part number of the SD Card connector was identified, but no luck finding a replacement part. An attempt was made to solder the tiny pin, which was successful.
Another R16 repair attempt: https://youtu.be/3QJDH4LFgnQ Power supply analysis and repair: https://youtu.be/wySRf2b0Low
#70 - Mackie 808s powered mixer repair
Something went horribly wrong in this mixer. There was a small fire that burned a hole in the PCB and destroyed a few components. Also there was a bit of a mystery with a peak detector in one of the channels. The damage was repaired and the peak detector was fixed as well.
#69 - Mackie SRM450v2 speaker repair
This active speaker did not power up. The problem turned out to be similar to the one we have seen before in the Mackie Thump TH-12A repair video: broken off pins from power diodes in TO-220 packages that are mounted on the back panel (heat sink).
Mackie Thump TH-12A repair: https://youtu.be/5zkEzjyKNjg
#68 - Using Agilent 661x for testing Li-ion batteries
Using an Agilent 661x power supply to charge and discharge Li-ion batteries is shown. This might be especially useful in the absence of an electronic load. These supplies are available for under $200, and proper electronic loads are usually more expensive.
#67 - Mackie PPM1008 powered mixer repair
According to the previous owner, this mixer was diagnosed in a local repair shop as having a power supply failure. I was told that the repair estimate was $500, so the mixer ended up being sold for $50 for parts or repair. I could not resist the temptation. The failure was traced to one 100V 3A schottky diode, which is $0.52 on Digikey. Wonderful mixer for a wonderful price!
#66 - Fluke 99 Li-ion charging mod
This is a followup to the Fluke 97 Li-ion Battery Upgrade video. A very cheap Fluke 99 was picked up on eBay with some problems. A Lipo pack was built for it. This time the charging voltage was adjusted from 8V to 8.4V, and also the charging current was doubled.
Fluke 97 Li-ion battery upgrade: https://youtu.be/pM8xTWhUnNk
Forum: https://www.eevblog.com/forum/testgear/using-li-ion-battery-in-fluke-97-scopemeter/
#65 - Mackie Thump TH-12A active speaker repair
One of these Mackie speakers did not power up. The problem was traced to a pair of power diodes in a TO-220 package that had two pins broken off. I am quite puzzled as to how this happened. Perhaps, the speaker was dropped, and the board flexed so much due to relatively heavy transformer. Strange things happen.
#64 - Bosch Power Max L2 charger repair
This Bosch Power Max EVSE stopped charging cars. The problem was traced to a broken wire inside of the J1772 handle. It seems like strain relief was not done properly. The main unit was also taken apart In the process with a closer look at the control board. The handle was fixed, and the charger is back in business.
DIY L2 charger project: part 1: https://youtu.be/JVhBMvj4KuA part 2: https://youtu.be/to4eYCJ4ZfM
Wikipedia page about SAE J1772 connector: https://en.wikipedia.org/wiki/SAE_J1772
#63 - Shure ULX microphone repair
This ULX2 transmitter with a classic SM58 head did not power up and had a burnt smell. The problem was traced to a tantalum capacitor that appeared to have caught fire, detached from the board and stuck between the battery terminals (what are the chances of that?) A proper disassembly procedure was shown.
#62 - Shure ULX transmitter repair
This is a professional wireless system by Shure with rack-mount ULXP4 receiver and ULX1 body-pack transmitter. The receiver did not show an active channel and battery status of the transmitter. A look at the RF spectrum showed that the so-called "tone key" signal was not transmitted. The problem was traced to a cracked soldering joint on one of the pins of a board-to-board connector.
#61 - Zoom power supply teardown and repair
Teardown, analysis and repair of the Zoom power supply that was found to be dead in the previous video. It seems that the supply did not survive some sort of a surge on the input, and there was no protection against that. The supply was repaired and some details of the design were discussed.
Previous video: https://youtu.be/3QJDH4LFgnQ
#60 - Zoom R16 repair fail
This Zoom R16 was picked up on eBay for parts or repair. It was described as not powering up. It turned out that both the external power supply and the R16 itself were dead. The NEC D78F0536 microcontroller seems to be faulty. No replacements are available and no firmware too. No way to proceed at the moment.
#59 - Harman Kardon AVR 235 receiver repair
This Harman Kardon AVR 235 receiver had no output. The problem was traced to a shorted ceramic capacitor in the power supply, which resulted in two blown fusible resistors. The process of investigation might be of interest to you.
Service manual: http://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Harman-Kardon-AVR-235-Service-Manual.pdf
#58 - Fluke 97 ScopeMeter battery upgrade
I got this meter quite cheap with no accessories and no battery pack. Replacement Ni-CD and NI-MH packs are sold for $20-30, but, instead of spending money on obsolete technology, I decided to figure out if I can use Li-ion cells to build a pack for free. I have plenty of various used cells salvaged from laptop packs and such. It turned out that it is easy to use 2-cell Li-ion packs in this meter. Such configuration is not perfect, but works fine. I ended up adding a battery management module for about $3 for extra safety and, hopefully, longer life of the pack.
Forum: https://www.eevblog.com/forum/testgear/using-li-ion-battery-in-fluke-97-scopemeter/
#57 - Agilent E3641A power supply repair
This power supply had non-functioning front panel (display, keypad and encoder). It turned out that three chips were dead in the front panel module: Intel 80C51 micro-controller, HV518PJ VFD driver and 74HC02 quad NOR gate. Fixing this took quite a bit of SMD and through-hole rework, and quite a bit of luck, especially finding the firmware for the micro-controller.
Forum: http://www.eevblog.com/forum/repair/agilent-e3641a-repair/
Replacement parts on DigiKey: AT89S51: https://www.digikey.com/product-detail/en/AT89S51-24JU/AT89S51-24JU-ND/1118890 HV518PG https://www.digikey.com/product-detail/en/HV518PJ-G/HV518PJ-G-ND/4902550
Firmware 34401-88804 rev01: http://www.ko4bb.com/getsimple/index.php?id=download&file=HP_Agilent/Agilent_34401A_E3646A_Display_board_MCU_firmware_dump_EPROM_34401-88804_RE-34401-88804.zip
34401A multimeter service guide with display and keyboard schematic : http://literature.cdn.keysight.com/litweb/pdf/34401-90013.pdf