To test switched mode power supply designs it is sometimes necessary to inject signal disturbances into the feedback loop to classify behavior. To do this you need a signal generator and oscilloscope or a network analyzer (expensive). You also need a way to decouple the signal generator from the circuit under test. One technique is to use a signal injection transformer. These too are unfortunately pretty expensive.
Following the guide here and eevblog posts here it is possible to make an injection transformer by hand.
I used the following parts:
- 50ohm bnc connectors
- 4.33” x 3.23” Hammond enclosure
- Two T60006L2030W514 cores
- 22 AWG stranded wire
- Zip ties
The cores were taped together to make handling easier.
A long pair of wires (about 60x the height of the core stack were cut). These were twisted together and wrapped onto the coil (about 25 windings round the core which is about as much as can fit. Others note a different core which allows for better spacing- though more windings is unlikely helpful).
Care was taken to note the matching ends of the winding before pairing each loop back to the coax connector (so that the phase / connection to the signal pin is same orientation).
Testing was done using a siglent SSA1104x-e as the oscilloscope, and a siglent SDG2042x as the waveform generator. Connections to the oscilloscope were BNC terminated with 50ohm through terminators.
A bode plot of 10Hz to 10MHz was taken.
The results are -3dB at 28.6Hz rising to flat at approx 110kHz and remaining flat to just under 1MHz before rolling off smoothly to -3dB at 5.6MHz.
It would be nice if the HF end was a little higher gain further out. But this will serve my purposes pretty well. And it’s a lot cheaper than $560 for a picotest.
Note ideally at least device under test end should be fused. I didn’t. I won’t be using this on particularly high voltage / current. But… I should have.
Soldering
Soldering Iron:
- Hakko FX951-66
Hot Air Rework:
- Hot air rework: Hot Air Rework Station, 861DW Hand Held Heat Gun 1000W SMD Reworking Station, Digital Heat Gun Soldering Rework Station with Air Nozzles Heat Device
- Tips / Nozzles: 9pcs/set 861DW Hot Air Gun Resisting Nozzles Quick 861dw Rework Station Heat Gun Resisting Nozzles 45 Degree Curved Angle Nozzle Sleeve for PCB Microscope Soldering Repair
Reflow:
- Heavily modified T962A reflow oven VEVOR Reflow Oven T962A 110V Reflow
Tips:
- T15-D08 chisel 0.8mm
- T15-D12 chisel 1.2mm
- T15-D24 chisel 2.4mm
- T15-D32 chisel 3.2mm
- T15-BCM2 2mm hoof for drag soldering
- T15-J02 bent tip 0.2mm
- T15-SB02 conical 0.2mm
- T15-SB02 long conical 0.2mm
- T15-BLL extra long conical 0.2mm
- T15-BC12 bevel 1.2mm
- T15-I short conical 0.2mm
- T15-SBC04 bevel 0.2mm
Sleeves:
Solder:
- Paste: MG Chemicals 4900P SAC305
- Fine 0.5mm: Kester 24-9574-7610 K100LD Lead-Free
- Coarse 0.8mm: Kester443-845 24-9574-7618 K100Ld Lead-Free
Paste / Flux Dispenser
- Paste extruder: Solder Paste Extruder, Solder Paste Dispenser Portable Semi Automatic Soldering Flux Glue Dispenser
Flux:
- Thick: MG Chemicals – 8341-10ML 8341 No Clean Flux Paste
- Thin: Chip Quik CQ4LF-1.0 Liquid Flux No-Clean
Dispenser needles:
- Needles: 120Pcs 1/2″ Industrial Liquid Dispenser Needle Adhesive Glue Dispensing Blunt Tip Luer Lock
Desolder wick:
Tip cleaner:
- Tip cleaner Soldering Tip Cleaner 599B Water-free Tip Cleaner Hakko
- Tip cleaner refills Hakko 599-029 Cleaning Wire for 599B Tip Cleaner
Work holding:
Fume extraction:
- Extractor: Triple Filters 120W Professional Strong Suction Fume Extractor for Electric Soldering Iron, Solder,Welding
- Replacement filters: Fume Extractor Triple Air Filtration System Replacement (10”× 12”) for Electric Soldering Iron Welding
Soldering mats:
- Soldering Mat Insulation Soldering Iron Kit Heat Resistant For Repairing Electronics Watch Laptop Soldering Station Tool For Hot Air Station (top)
- Multipurpose Silicone Mats, Countertop Protector, 23.6×15.7×0.08 Inches, Extra Large, Thick Silicone Counter Mat, Heat-Resistant, Non-Slip, Dark Blue (bottom)
Tools
Tweezers:
- Angled: Vetus ESD Tweezers Pro Precision Curved Tweezer Anti-Static SMD Black Fine Tip Tweezer
- Straight: Vetus Anti-static SMD Black Tweezer Non-magnetic Stainless Steel Pointed Tip
Snips:
Wire cutters:
- Fine: Engineer PA-06
- Coarse: Engineer PA-07
Crimps:
- Taiss JST Crimping Tool,Dupont Crimping Tool,JST Crimper,Dupont Crimper,Ratcheting Wire Crimper for JST Connector XH 2.54mm,PH2.0,D-sub Terminals,(0.08-0.5mm² 28-20AWG) for JST
- HKS Ferrule Crimping Tool Kit – Square Ferrule Crimper Plier (AWG 23-7) with 1900pcs Wire End-Sleeves Terminals Kit for ferrules
- iCrimp SN-28B Dupont Crimping Tool for 3.96mm, 2.54mm, 2.5mm Pitch Dupont, JST XH VH Connectors, AWG 18 to 28 for dupont / JST
Screwdrivers:
- iFixit Mako Driver Kit – 64 Precision Bit Set for Electronics Repair smaller set
- iFixit Manta Driver Kit – Household, PC, Phone, Electronics Bit Set for larger set
Knife
- Blade holder: X-ACTO XZ3601 No. 1 Z-Series Precision Utility Knife w/Replaceable Steel Blade, Safety Cap
- Blades: X-ACTO 11 Classic Fine Point Replacement Blades, 40 Count
Files:
- Fine files for board nibbles etc: SE 73810DF 10-Piece Mini Diamond Needle File Set, 150 Grit – Assorted Shapes, 3-1/4″ Length – Ideal for Jewelers, Wood, Stone, Glass, Gemstones
Calipers:
- Measurement caliper: Digital Caliper, DCLA-0605 0-6 Inch/150mm, Inch/Millimeter/Fraction Conversion, Stainless Steel, Large LCD Screen
Lab Equipment
Oscilloscope:
- Oscilloscope: Siglent Technologies SDS1104X-E 100Mhz Digital Oscilloscope 4 channels Standard Decoder
- 200Mhz Probe: PP215 200 MHz Oscilloscope Probe
- 100Mhz Probe: PP510 100 MHz Oscilloscope Probe
- Logic probe for SDS1104X-E: Siglent Technologies SLA1016 Mixed Signal Hardware Option for The Four Channel SDS1000X-E and SDS2000X-E Oscilloscope Series
FTDI and programmers:
- Bitmagic logic analyzer
- Tigard Protocol Tool – these are seriously awesome and work with OpenOCD for flashing chips via SWD etc
- JTAG ribbon cable for tigard
- JTAG SWD 10pin IDC Cable
- Bitmagic Basic 0.1in Pin Header Flywire Cable
- BitMagic – Mini Test Hooks
- Black Magic Probe V2.3
Power supply:
- RD6006PW 60V 6A DC DC Step Down Power Supply Whole Set not assembled (RD6006PW+ S400 case+ 400W PSU)
- RD RD6024W 60V 24A DC DC Step Down Power Supply Whole Set not Assembled (RD6024W+S800 case+1200W68V PSU)
Signal Generator:
- Signal generator: Siglent Technologies SDG2042X Arbitrary Waveform Function-Generators, 40 MHz, Grey
- BNC Test leads: Pomona 5187-C-36 Bnc (M)/Grabber, Rg58C/U
- BNC cables: Fluke Pomona 2249-C-24 Bnc (M), Rg58C/U
Electronic load
Multimeter:
Optical
Wearable Magnifiers:
- Headband magnifiers: Elikliv Headband Magnifying Glass with Light 1X to 14X, Rechargeable Handsfree Head Mount Magnifier
Microscope:
- Microscope: AmScope SM-4B Series Binocular Zoom Stereo Microscope 3.5X-45X Magnification on Double Arm Boom Stand
- Lighting: AmScope 144 LED Intensity-adjustable Ring Light for Stereo Microscopes with White Housing
Wire and Components
Hookup / rework wire:
- Coarse (32AWG): BNTECHGO 32 AWG Magnet Wire – Enameled Copper Wire – Enameled Magnet Winding Wire – 4 oz – 0.0078″
- Finer: Insulated 0.02mm 120M Phone Motherboard Fingerprint Jump Wire Soldering Pure Copper Conductor Wire Phone Chip Conduction Wire for Phone PCB BGA Soldering Repair
Cable construction:
- Stranded 22AWG: 22AWG Stranded Wire 22 Gauge Wire Tinned Copper Hookup Wire kit with PVC Insulated, 6 Colors (33 Feet/10 M Each) Electrical Wire
- Stranded 26AWG: 26 AWG Gauge UL1061 Stranded Hook Up Wire Kit, 300V, 0.039″ Diameter, 25 ft Length Each, 6 Colors
Fixed hookup:
Caps:
- 0603 Cap library: Capacitor 0603 (0.5pF-2.2uF) 90 Value x 50pcs = 4500pcs SMD Capacitor Combo SMT Sample Book Kit Electronic Component
- 0805 Cap library: 0805 (0.5pF-10uF) 92 Value all Series SMD Capacitor Combo Sample Book Kit SMT Pack Box Book RoHS
- 0402 Cap library: Capacitor 0402 (0.5pF-1uF) 80 Value x 50pcs = 4000pcs SMT Capacitor Kit SMD Combo Sample Book Electronic Components
Resistors:
- 0805 Resistor library: 0805 0R-10M & 1pF-2.2uF 1% Resistor and Capacitor Mixed Practical Kit SMD Assorted Resistors Sample Book Combo Pack
- 0805 Restors in sorted boxes: 0805 SMD Resistor Assortment Kit,Resistor Pack of 7200 Pieces 72 Values(Each Value 100 Pcs)±1% Tolerance (0 Ohm-10 Mega Ohm) Thick Film Chip Resistor Kit Rohs Compliant
- 0402 Resistor library: 1% R0402 SMD Resistor Assorted Folder (0 ohm-10M ohm) 170value x 50pcs = 8500pcs Sample Book
Disposables
Gloves:
Painters tape for holding solder paste stencils etc:
Kapton tape:
- High Temperature Tape, 1 Mil Thick, 1 Inch Wide x 36 Yards Long, Polyimide Film with Silicone Adhesive
- High Temperature Heat Resistant Tape for Heat Transfer 3D Printers High Temp Tape,Kapton Tape Electronics Polyimide Tape 1 inch 36yds
Isopropyl Alcohol:
Storage:
- SMT boxes: SMD SMT Electronic Box IC Electronic Components Plastic Storage Case Small Parts Tool Box 75×31.5×21.5mm
- SMT boxes small: 50Pcs Electronic Component Organizer, Green SMT SMD Container Box Mini Storage Case for Electronic Components Free Combination
- Tool box: EMENTOL 2PCS Multi-Purpose Portable Organizer Box Set with 44-Removable Compartments, 2 Pieces Professional Boxes with Dimension 16.2″L*13″W*2.3″H
- Small tool boxes: Toolbox Organizer – Tool Organizer Nail Organizers – Parts Case Storage Box – Screw Nuts and Bolt Electronic Component Storage Bin – Compartment Hardware Tool Box with Dividers (3 Piece Set)
- 6 mil 6×8 bags for parts
I strongly recommend reading 1bitsquared’s blog post and This hackaday post before deciding to buy a T962A oven.
The short version is that getting these to work reliably is a /lot/ of work.
Issues Include:
- Poor temperature profile following
- Uneven heating causing scorching in places even whilst other areas do not reflow
- Lack of internal convection leading to uneven heating
- Unshielded infra red bars causing hot spots
- Poor default firmware
- Masking tape internally that will stink when it burns
- Lack of grounding
However good reflow ovens are expensive. And with some work you can get these functional – even for relatively large boards. This makes them a reasonable – albeit time consuming way to get a reflow oven at affordable cost.
Several other sites (listed above) have better guides on what first steps to take.
Required mods:
- Fix the grounding – do this first
- Fix the masking tape and replace with Kapton – also do this before plugging in or turning on the oven
- Flash the firmware to unified engineering’s firmware: UnifiedEngineering T962 firmware
Additional fixes:
- Add better thermocouple interface – I used this one https://github.com/UnifiedEngineering/T-962-improvements/wiki/Better-thermocouple-interface and followed the instructions there for wiring it up
- More thermocouples allows us to average more places in the oven. To do this I hacked the firmware to allow calibration of pairs of sensors and average them all – see my GitHub fork for T962A firmware
- Allow thermocouples to be nearer to the PCB – this is a tradeoff. You can mount directly on the board and deal with thermocouple wires and fixing the TC to the board all the time, or you can install additional thermocouples in tubes near the board. I did the latter using threaded metal tubes usually used for lighting fixtures
- Add additional thermocouples:
- More thermocouples allows us to average more places in the oven. To do this I hacked the firmware to allow calibration of pairs of sensors and average them all – see my GitHub fork for T962A firmware
- Allow thermocouples to be nearer to the PCB – this is a tradeoff. You can mount directly on the board and deal with thermocouple wires and fixing the TC to the board all the time, or you can install additional thermocouples in tubes near the board. I did the latter using threaded metal tubes usually used for lighting fixtures
- I also put them at slightly different heights to allow for better averaging – the existing TCs are near the top of the oven and will read hotter than the board
- Seal the front of the oven with gas grill seals so that airflow from the front doesn’t drop the temperature at the front of the oven.
- Measure and calibrate your thermocouples against various locations on the PCB. I use this sheet here which allows calculation of calibration mapping from the MAX TC probes to probes on a PCB which are what we ideally want. I measured several locations, and select two curves for calibration which get entered into the firmware
- Develop and tweak your own paste profiles using the same link you can develop a curve based on manufacturer instructions for the paste.
- I can now successfully reflow boards of about 8in x 8in in solder free paste which was certainly not possible before