2 layers100.5 × 66.5 mm
2 layers101.5 × 63 mm
N24 ACAmplifier
deqit/PhilipsPM25283Hardware and software for the Philips PM2528
- Size
- 101.5 × 63 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 114
- Nets
- 78
- Pads
- 290
- Tracks, vias
- 0, 0
- Routed
- Not yet
- KiCad
- KiCad 9.0 (file 20241229)
- Created
- 8 Aug 2025
- Updated
- 7 Nov 2026
Overview
N24 ACAmplifier is an open-source printed circuit board by deqit, from the deqit/PhilipsPM2528 repository on GitHub. It is a 2-layer board of 101.5 × 63 mm with 114 parts on 78 nets.
It is built around the BC547B, BAW62 and BC557B, with the BZX79-B8V2, BZX79-C3V0 and HEF4047BT among its other parts. Its parts include 53 resistors, 25 capacitors, 1 diode and 1 crystal.
Main components
7
BC547B
TO-921 NPN 100mA 100nA 150MHz 200 300mV 45V 625mW 6V NPN TO-92 Bipolar (BJT) ROHSLGEBipolar (BJT)
BAW62
DO-351V@100mA 300mA 4ns 500mW 5uA@75V 75V DO-35 Switching Diodes ROHSonsemiSwitching DiodeBC557B
TO-921 PNP 100mA 100nA 150MHz 180 45V 5V 625mW 650mV PNP TO-92 Bipolar (BJT) ROHSLGEBipolar (BJT)
BZX79-B8V2
SOD27(DO-35)-65℃~+200℃ 1 Independent 15Ω 500mW 700nA@5V 8.04V~8.36V 8.2V SOD27(DO-35) Zener Diodes ROHSNexperiaZener DiodesBZX79-C3V0
SOD27(DO-35)-65℃~+200℃ 1 Independent 10uA@1V 2.8V~3.2V 3V 500mW 80Ω SOD27(DO-35) Zener Diodes ROHSNexperiaZener Diodes
HEF4047BT
SOP-14-40℃~+85℃ 1 4.5V~15.5V 4000B 50ns 600uA Complementary type Monostable、Astable Retriggerable、Reset SOP-14 Monostable Multivibrators ROHSNexperiaMonostable Multivibrators
LM393N
DIP-80℃~+70℃ 2 2.5mA 250nA 2V~36V 36V 5mV 5nA Fail-safe function Open-drain ±16V DIP-8 Comparators ROHSHGSEMIComparators
README
README.mdReviving a Philips PM2528 Digital Multimeter
Picked up this vintage multimeter a while back. Half-functional, no manuals, and full of mystery. Perfect!
It’s built around an Intel 8035 microcontroller and packed with analog boards. There wasn’t a complete service manual anywhere, so I decided to dive in myself. This project's become a learning experience in hardware reverse engineering, firmware disassembly, and documentation.
Also see https://hackaday.io/project/203720-reviving-a-philips-pm2528-digital-multimeter
The project
The goal of this project is fixing the multimeter. Well... maybe not really. In real life, the road towards that goal is much more interesting. And I'm documenting everything I found along the way.
In this repository you'll find:
- Original Philips-documentation (at least, what I could find, unfortunately in lo-res)
- Schematics (KiCad)
- PCB Layouts (KiCad)
- Schematic/PCB of a risercard, for testing the expansionboards
- Disassembled firmware, including annotations (Ghidra)
- A lot of documentation regarding relais-mapping, IO-expander-ports, etc.
- Detailed scope- and logic analyzer screenprints and capture-logs
- Deepdive: Explaination of how-everything-works
- etc.
Everything you find here is work-in-progress. It might be incomplete, and some parts may not be 100% accurate yet. If you spot something interesting or catch an error, feel free to drop me a message.
The components
Overview
- See PM2528 Overview
Risercard
- See PM2528 Risercard
ADC
Parts
114| Qty | Value | Footprint | References |
|---|---|---|---|
| 4 | 1k05 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2412, R2445, R2451, R2452 |
| 4 | 22n | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2421, C2422, C2423, C2424 |
| 4 | 46k4 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2418, R2419, R2423, R2449 |
| 4 | 71R5 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2440, R2441, R2443, R2444 |
| 3 | 1M00 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2401, R2407, R2411 |
| 3 | BC547B | Package_TO_SOT_THT:TO-92_Inline | V2405, V2406, V2413 |
| 3 | BF199 | Package_TO_SOT_THT:TO-92_Inline | V2411, V2412, V2415 |
| 2 | 10M | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2417, R2428 |
| 2 | 10n | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2413, C2417 |
| 2 | 15k4 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2410, R2448 |
| 2 | 1k21 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2416, R2446 |
| 2 | 2k15 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2431, R2437 |
| 2 | 2k74 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2409, R2425 |
| 2 | 30k1 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2450, R2453 |
| 2 | 681k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2405, R2408 |
| 2 | 6n8 | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2419, C2420 |
| 2 | 6u8 | Capacitor_THT:CP_Radial_Tantal_D4.5mm_P5.00mm | C2409, C2410 |
| 2 | 7R5 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2435, R2436 |
| 2 | 8k25 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2420, R2421 |
| 2 | BAV45 | Package_TO_SOT_THT:TO-72-4 | V2419, V2420 |
| 2 | BAW62 | Diode_THT:D_DO-35_SOD27_P10.16mm_Horizontal | V2421, V2422 |
| 2 | BC557B | Package_TO_SOT_THT:TO-92_Inline | V2407, V2408 |
| 2 | BFW11 | Package_TO_SOT_THT:TO-72-4 | V2409, V2410 |
| 2 | BZX79-B8V2 | Diode_THT:D_DO-35_SOD27_P10.16mm_Horizontal | V2423, V2424 |
| 2 | ~ | Connector_Pin:Pin_D0.9mm_L10.0mm_W2.4mm_FlatFork | TP2402, TP2403 |
| 1 | 0V | Connector_Pin:Pin_D0.9mm_L10.0mm_W2.4mm_FlatFork | TP2405 |
| 1 | 10k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2424 |
| 1 | 12p | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2416 |
| 1 | 13n3 | Capacitor_THT:C_Axial_L5.1mm_D3.1mm_P15.00mm_Horizontal | C2408 |
| 1 | 140 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2427 |
| 1 | 150 | PM2528:Trimmer vertical | R2422 |
| 1 | 150p | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2412 |
| 1 | 15K4 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2447 |
| 1 | 15R4 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2404 |
| 1 | 15p | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2415 |
| 1 | 17k8 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2414 |
| 1 | 1k | PM2528:Trimmer vertical | R2415 |
| 1 | 1k78 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2426 |
| 1 | 1n8 | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2414 |
| 1 | 205 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2432 |
| 1 | 215 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2439 |
| 1 | 21R15 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2442 |
| 1 | 220k | PM2528:Trimmer vertical | R2406 |
| 1 | 220n | Capacitor_THT:C_Rect_L13.0mm_W4.0mm_P10.00mm_FKS3_FKP3_MKS4 | C2406 |
| 1 | 220p | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2404 |
| 1 | 22n | Capacitor_THT:C_Rect_L13.0mm_W4.0mm_P10.00mm_FKS3_FKP3_MKS4 | C2401 |
| 1 | 22u | Capacitor_THT:CP_Radial_Tantal_D4.5mm_P5.00mm | C2407 |
| 1 | 2k37 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2434 |
| 1 | 2k61 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2433 |
| 1 | 301k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2429 |
| 1 | 330n | Capacitor_THT:C_Rect_L18.0mm_W5.0mm_P15.00mm_FKS3_FKP3 | C2411 |
| 1 | 33n | Capacitor_THT:C_Rect_L13.0mm_W4.0mm_P10.00mm_FKS3_FKP3_MKS4 | C2403 |
| 1 | 39p | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2425 |
| 1 | 3p9 | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2405 |
| 1 | 4k64 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2438 |
| 1 | 560p | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2418 |
| 1 | 60k4 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2430 |
| 1 | 634k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2413 |
| 1 | 8p2 | Capacitor_THT:C_Disc_D4.3mm_W1.9mm_P5.00mm | C2402 |
| 1 | 95k3 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2402 |
| 1 | 9k53 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2403 |
| 1 | A | TestPoint:TestPoint_Bridge_Pitch5.08mm_Drill0.7mm | JP2401 |
| 1 | AC_RMS? | Connector_Pin:Pin_D0.9mm_L10.0mm_W2.4mm_FlatFork | TP2406 |
| 1 | B | TestPoint:TestPoint_Bridge_Pitch5.08mm_Drill0.7mm | JP2402 |
| 1 | BF324 | Package_TO_SOT_THT:TO-92_Inline | V2416 |
| 1 | BFQ14 | Package_TO_SOT_THT:TO-75-6 | V2404 |
| 1 | BFW13 | Package_TO_SOT_THT:TO-72-4 | V2402 |
| 1 | BSV81 | Package_TO_SOT_THT:TO-72-4 | V2401 |
| 1 | BZX46-C2V0 | Diode_THT:D_DO-35_SOD27_P10.16mm_Horizontal | V2418 |
| 1 | BZX79-C3V0 | Diode_THT:D_DO-35_SOD27_P10.16mm_Horizontal | V2417 |
| 1 | Fchop | Connector_Pin:Pin_D0.9mm_L10.0mm_W2.4mm_FlatFork | TP2401 |
| 1 | HEF4047 | Package_DIP:DIP-14_W7.62mm | D2401 |
| 1 | Jumper_2_Small_Bridged | TestPoint:TestPoint_Bridge_Pitch5.08mm_Drill0.7mm | JP1 |
| 1 | LM308AH | Package_DIP:DIP-8_W7.62mm | A2401 |
| 1 | LM393N | Package_DIP:DIP-8_W7.62mm | A2402 |
| 1 | OUT | Connector_Pin:Pin_D0.9mm_L10.0mm_W2.4mm_FlatFork | TP2407 |
| 1 | something | Connector_Pin:Pin_D0.9mm_L10.0mm_W2.4mm_FlatFork | TP2404 |
| 1 | ~ | PM2528:PM2528_RiserCardConnector | X2401 |
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Questions
How big is the N24 ACAmplifier PCB?
It measures 101.5 × 63 mm and has 2 copper layers, 1.6 mm thick.
What parts does the N24 ACAmplifier use?
114 parts, built around the BC547B, BAW62, BC557B and BZX79-B8V2. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the N24 ACAmplifier KiCad files?
From the deqit/PhilipsPM2528 repository on GitHub, at the commit this page was made from: the board is Schematics/Expensionboards/N24_ACAmplifier/N24_ACAmplifier.kicad_pcb and its schematic Schematics/Expensionboards/N20_ADCControl/N20_ADCControl.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the N24 ACAmplifier design in my own project?
Its repository states no licence, so its author keeps all rights: ask deqit before reusing the design.