Troubleshooting this PCB

[Carmet L]

Hello

Can anybody help troubleshoot this PCB ?

The PCB is getting power, but not spinning the drive up only BSY light is lighted in Status Register lights.

The second photo shows component has been fluxed residue and possibly removed and refitted. Somebody has fiddled drive before come to us.

What can be done to check health of PCB please ?

[pbzcbf...@gmail.com]

Measure the voltages at the 4R7 coil and the two SOT89 components. In fact, one of the SOT89 chips (in the second photo) appears to be damaged.

[Carmet L]

Thanks you.

Which are the SOT89 pieces please? 

[img]

"A2YT" is blown, there's a hole in the middle.

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[pbzcbf...@gmail.com]

SOT89 is a package style.

https://www.google.com/search?imgtype=photo&q=SOT89&tbs=isch%3A1%2Cisz%3Am&udm=2

[Carmet L]

Thanks you.

I have left the office now, but will make multimeter tests on these components when I return and report back.

If they SOT89 pieces are damaged, what can I do to fix them ?

[img]

"A2YT" marked component is the one in SOT89 form factor, because we're talking about the same piece.

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[pbzcbf...@gmail.com]

Well, you can replace them, but you will probably find that there is more damage downstream. If so, then it would be more expedient, and potentially cheaper, to replace the PCB with one that has the same firmware version.

[img]

I forgot to mention: you have to replace those with good ones from an identical donor board.

[pbzcbf...@gmail.com]

Did you check the zero-ohm resistor ("000") near the power connector?

[pbzcbf...@gmail.com]

After closer examination of the hi-res photo, the "damage" on A2YT looks more like a mould mark.

[pbzcbf...@gmail.com]

Can you reflow these dry solder joints?

[pbzcbf...@gmail.com]

Test points.

[Carmet L]

Thank you for your help with this.

I have tested the things you suggest and have the results below, and have added some higher-res pics if needed.

I have not reflowed anything just yet.

Measure the voltages at the 4R7 coil and the two SOT89 components. In fact, one of the SOT89 chips (in the second photo) appears to be damaged

4R7 – 2.06v either side

SOT89 (A2YT)

• top side 5v
• pin furthest away from resistor 4v
• middle pin 5v
• pin nearest resistor (Vio1) 3.4v

SOT89 (B2YS)

• top side 2v
• pin nearest resistor 1.95v
• middle pin 2v
• pin furthest away from resistor 1.25v

 

Did you check the zero-ohm resistor ("000") near the power connector?

12.35v on either side

Regs

Vio1 – 3.4v

CA2 – 0.3v

Vio2 – 1.25v

 

Vcore

4R7 bottom pin – 2v

Resistor bottom pin – 2v

 

Preamp Supplies

+/- 5v – 3.38v

Ferrite bead 1 – 0.3v

Capacitor 1 – 0.3v

Capacitor 2 – 5v

Ferrite bead 2 – 0.3v

Thank you.

On Tuesday, 18 November 2025 at 20:23:53 UTC pbzcbf...@gmail.com wrote:

Test points.

[pbzcbf...@gmail.com]

Sorry, I mixed up Vio2 and Vcore. They should be swapped, but otherwise they appear OK.

The -5V supply for the preamp is missing. This is generated by the motor controller. In other designs the MCU commands the motor controller to switch this supply on or off. I don't know what is supposed to happen on this board. You would need to examine the terminal log. That will tell you if the MCU is functional.

[Carmet L]

The -5V supply for the preamp is missing.

I did measurement of each side of the 101 piece, and it was 3.38v

You would need to examine the terminal log. 

This is strange because the terminal is blank; no matter how I try to plug it into the socket, it still shows nothing output in the terminal window, as if it is not connected at all.

[pbzcbf...@gmail.com]

My annotations appear to have confused you. The +5V and -5V preamp supplies are the two circled test points, not the 101 resistor.

It appears that the MCU is not communicating. The MCU could be bad or it could be that the crystal or the Atmel flash is faulty.

[Carmet L]

Ok thanks for showing that out.

Best to find a replacement PCB rather than troubleshoot this further because it might to have a significant problem.