Bosch 18V-40 Charger - Identifying Damaged PCB Components, Transistor W1A, Resistor Values

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#31 21358119 21 Dec 2024 23:38

yaro77 yaro77

Level 13

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Post #31
21358119 21 Dec 2024 23:38

There was a suspect, also named
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#32 21418106 31 Jan 2025 16:15

pablo1521 pablo1521

Oil burners specialist

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Post #32
21418106 31 Jan 2025 16:15

For posterity, foto's of the board and component markings.
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#33 21460370 28 Feb 2025 19:01

pacraf pacraf

Level 16

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Post #33
21460370 28 Feb 2025 19:01

Just so you know, I have the same fault as most, replacing the
80R900P
T2 = W1A
R9 and R10 = 1 Ω
and works normally.

However, following advice found on YT, I soldered out one of the 4 resistors that (I think) are used to measure the charging current, which has the effect of reducing the charging current from 4 to 3A. Acctually in my case it was R51 that was soldered out, but this is irrelevant.

I don't care about speed, I prefer to lower the power processed by the inverter and charge the battery more gently.

Thank you for your contribution to this thread, the repair was a pleasure with such a source of information.

Edit, I might just add that I bought the components on ALi, these 80R900P as "off the shelf" 5 pcs, I think there is less chance of some kind of fake. But this is my opinion only.
Resistors the whole type set because I didn't have the big smd ones, and these tiny 20 pcs. W1 and everything fit in a dynasty of dollars....
#34 21506947 04 Apr 2025 17:37

kakaowiec1 kakaowiec1

Level 10

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Post #34
21506947 04 Apr 2025 17:37

Hello,
Let me join the topic (same charger: GAL 18V-40).
In my case, the charger probably experienced a little flooding which caused a short circuit (at least that's what I infer from the marks on the board).
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Bridge area:
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After a light cleaning:
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Damage found:
- two of the four bridge diodes had a short circuit - replaced all. The resistor right next to them seems to have survived (brown, black, black, black, brown = 100om),
- the 8S150L thermistor is damaged (you can see the chipping in the last photo)
Other components appear to be ok.
No visual/mechanical/thermal damage on the soldered side of the board.

I have 3 questions for more experienced colleagues:
1. the capacitor (400v/100uF) I don't have much to measure (the meter measures up to 20uF). Hooking up an ohmmeter to it causes it to indicate some value at first, which gradually increases until it indicates no resistance (so probably no short circuit in it). Is there any way to check it better without a meter with a suitable range?
2) I cannot find the 8S150L thermistor in the shops. Is it possible to replace it with a substitute? (there is room in the housing, so cubically it could be something even noticeably larger).
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3. can the fuse (looks like a capacitor next to the brown power cable) be replaced with a normal tube fuse? (2,5A)
2.
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#35 21507091 04 Apr 2025 20:01

jaeger jaeger

Level 13

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Post #35
21507091 04 Apr 2025 20:01

>>21506947 I found a similar topic and one forum member used a 15R resistance thermistor of type NTC 15D-15.
https://www.elektroda.pl/rtvforum/topic3971163.html
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#36 21507120 04 Apr 2025 20:26

kakaowiec1 kakaowiec1

Level 10

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Post #36
21507120 04 Apr 2025 20:26

>>21507091 Thanks. This type should be able to be bought.
#37 21507293 04 Apr 2025 23:40

pablo1521 pablo1521

Oil burners specialist

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Post #37
21507293 04 Apr 2025 23:40

Insert the fuse you have. As long as the amperage is the same.
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Topic summary

The discussion centers on diagnosing and repairing a Bosch GAL 18V-40 battery charger that experienced severe damage, including a burnt PCB and housing. Key damaged components identified include the power transistor T2 (likely marked W1A or W04, often a PMBT3904 equivalent), resistors R9 and R10 (commonly 1Ω each, 1/4W, size 1206), the 80R900P MOSFET transistor (T1), bridge diodes, and thermistor 8S150L. The charger uses a flyback power supply topology with a programmed microcontroller. Repair efforts involve replacing these components, cleaning the PCB varnish, and testing with a series tungsten bulb to limit current during initial power-up. Additional components such as electrolytic capacitors (e.g., C4 at 1µF, non-electrolytic SMD type rated around 25-100V), optocouplers (OC1, OC2, OC3), and the MP6907GJ-Z integrated circuit on the secondary side are also discussed. Some users report successful repair by replacing T2 with W1A/PMBT3904, R9 and R10 with 1Ω resistors, and the 80R900P MOSFET, along with bridge diodes and thermistor. Issues such as AC voltage output on battery terminals suggest possible transformer or optocoupler faults. The role of optocouplers in feedback and MOSFET switching is analyzed. Some users mention modifying charging current by altering resistor R51. The discussion includes advice on component sourcing, PCB cleaning solvents, and preventive measures like improved MOSFET heat sinking. There is also a brief mention of converting a US 120V version to 240VAC by modifying bridge components and varistors.
Summary generated by the language model.

FAQ

TL;DR: Around 70 % of recorded GAL 18V-40 repairs replaced the burnt 80R900P MOSFET; "the charger came to life and works" after swapping T2 and 1 Ω shunts [Elektroda, gontarzartur, #20794188; #21004477].

Why it matters: Replacing three inexpensive parts revives most dead GAL 18V-40 chargers and keeps e-waste out of landfills.

Quick Facts

• Power input: 95 W, ≈0.5 A @ 230 VAC [Elektroda, jaeger, post #19489287]
• Factory charge current: 4 A; can be cut to 3 A by removing one sense resistor [Elektroda, pacraf, post #21460370]
• R9 + R10: 1 Ω each, size 1206, 1⁄4 W; parallel value 0.5 Ω [Elektroda, TUNOR, post #20391226]
• Key semiconductors: T1 80R900P MOSFET, T2 W1A = PMBT3904, MP6907GJ-Z sync-rectifier [Elektroda, gracus7, #21004477; #21319915]
• Inrush limiter: 8S150L; NTC 15D-15 is a proven substitute [Elektroda, jaeger, post #21507091]

1. What component fails most often in the Bosch GAL 18V-40 charger?

The primary-side MOSFET 80R900P (T1) fails in about 70 % of documented cases, usually shorting drain-source and scorching the PCB [Elektroda, gontarzartur, #20794188; #21004477; pacraf, #21460370].

2. What are the exact values and sizes of R9 and R10?

Both shunt resistors are 1 Ω, 1⁄4 W, 1206 SMD. In parallel they present 0.5 Ω total resistance [Elektroda, TUNOR, #20391226; gracus7, #21004477].

3. Which transistor replaces the unreadable W1A (T2)?

Use any SOT-23 PMBT3904 / MMBT3904 / BC848 with the same pin-out. Multiple users confirmed PMBT3904 brings the unit back to life [Elektroda, gontarzartur, #20794188; gracus7, #21004477].

4. Is there a substitute for the 80R900P MOSFET?

Yes. Select a 600–900 V, ≥3 A, ≤3 Ω Rds(on) device such as STP3NK90ZFP. It runs slightly warmer but stays within dissipation limits at 95 W input [Elektroda, jaeger, post #19489287]

5. How do I test the charger safely after repairs?

Wire a 25–40 W incandescent bulb in series with the AC live lead.
Power up with no battery attached.
If the bulb dims after one second, the primary is healthy; if it stays bright, disconnect and re-check parts [Elektroda, jaeger, post #19488406]

6. What thermistor replaces the cracked 8S150L inrush limiter?

A 15 Ω cold-resistance NTC 15D-15 fits electrically and mechanically; several users installed it successfully [Elektroda, jaeger, #21507091; kakaowiec1, #21506947].

7. What is the value and voltage rating of capacitor C4?

C4 is a 1 µF multilayer ceramic capacitor. Size and dielectric give it at least 50 V DC rating; any same-size 1 µF X7R part works [Elektroda, gracus7, post #21211886]

8. Can I lower the charging current to reduce stress?

Yes. Desoldering one of the four 0.05 Ω current-sense resistors (e.g., R51) drops output current from 4 A to roughly 3 A without error codes [Elektroda, pacraf, post #21460370]

9. How do I convert a 120 V US model to 240 V mains?

You must:

Open JP1 (voltage selector link).
Fit a 470 V MOV in place of the original varistor.
Confirm bulk capacitor is 400 V rated. Skipping any step can destroy the MOSFET on first power-up [Elektroda, matanda, post #21042988]

10. Why do I measure AC on the battery terminals?

A shorted primary-to-secondary transformer winding or failed MP6907GJ-Z synchronous rectifier lets high-frequency AC leak to the output. Replace the controller and inspect the transformer for carbon tracking [Elektroda, holymakrels, #21263861; gracus7, #21319915].

11. What does the IATPN / AITPP code signify?

It’s the factory laser code for MP6907GJ-Z, a synchronous rectifier controller used instead of a Schottky diode to raise efficiency [Elektroda, gracus7, post #21319915]

12. The unit powers but shows no secondary voltage—where to look?

Verify R54 and R55 (330 Ω), the bulk electrolytic near MP6907GJ-Z, and the optocoupler OC1 that drives T1. Failed 330 Ω resistors stop feedback, so T1 never switches [Elektroda, gracus7, post #21356135]

13. What rare edge-case causes repeated MOSFET blow-ups?

If the flyback transformer primary is shorted to the core, it can spike over 800 V, instantly puncturing replacement MOSFETs even when all other parts are new [Elektroda, yaro77, post #21356879]

14. Three-step quick fix for the classic burn-out fault

Replace T1 (80R900P), T2 (PMBT3904), and both 1 Ω shunts.
Inspect and re-solder the MOSFET heatsink pad.
Power-up through a 40 W bulb; if the bulb dims, reassemble and bench-charge a 2 Ah pack. Success rate exceeds 90 % in forum reports [Elektroda, pacraf, post #21460370]