I'd sure be happy if someone had the same board and was able to send me a pic of that QA1 😀

Is that 3B written on the transistor? it could be BC856 PNP transistor: https://www.s-manuals.com/smd/3b

Here are som better images.
There is +5V from L17, and +12V on that tiny trace that buggers off.
I will try to find where it is going (RA1 seems like a good candidate)

Checked. The via buggers of to that Tantalum positive side. RA1 is 10kOhm and connected to the 12V rail (directly to the ATX-connector).
A PNP or P-channel fet?
Update: The +5V is measured, but there's a 50 ohm resistance on the way to the +5V rail. I will have to find the resistor.
Sure could use a schematic 😀

The number looks like 35 or maybe 3S, both are P-channel mosfet in sot-23 package:
https://www.s-manuals.com/smd/35
https://www.s-manuals.com/smd/3s

I replaced it with a generic P-fet. The clock generator gets voltage and does give a waveform out.
Still, no post. Without a CPU, VCC is 5V which is a bit troubling

I swapped the FET's some near equivalent (NDP603AL -> STP40NF03L) and that diode.
Still, 5V to CPU without a CPU inserted.

Looking for any good ideas what to look at next

So I finally tested the CPU in a working system (Also with K6-2/300, so direct swap). No life in the CPU.
Sigh, I'd need some "expendable" CPU's to try out on this possibly repaired board

Have you tried different voltage settings by setting the jumper? Are they all delivering 5V?

It's not the jumpers, this motherboard does not support 5V CPUs (P5).
This 72jXQ would need to be id'd and replaced. Either this or the AR7010 - or both.
72jXQ (Q6) seems dead, atleast 1P (Q5) was dead.
Q5 was replaced with Q7.

oh2ftu wrote on 2023-09-02, 15:53:

It's not the jumpers, this motherboard does not support 5V CPUs (P5). This 72jXQ would need to be id'd and replaced. Either this […]
Show full quote

It's not the jumpers, this motherboard does not support 5V CPUs (P5).
This 72jXQ would need to be id'd and replaced. Either this or the AR7010 - or both.
72jXQ (Q6) seems dead, atleast 1P (Q5) was dead.
Q5 was replaced with Q7.

I know it doesn't support 5V CPUs, but it still should have jumpers for 2.2-3.2V. What I meant that have you tested if the board delivers same 5V to CPU with different jumper settings, ie 2.2V, 3.2V? There needs to be regulation for different voltages and maybe this helps you to track the fault if some voltage settings work correctly.

Ok.
So Q5 is most probably NPN driving the primary FET.
The base is pulled up via a 2,2k resistor. It's also connected to the drain of Q6.
Q6 is an N-fet(?) and the gate should be pulled low for the source (GND) to pull Q5 low and thus quench the power output of the primary FET.
So ... either the replacement Q6 I placed is broken or not an N-fet (marked K72) OR the AR7010 should have an internal pulldown, or pull low, pin 8 (output) - which is connected to the Q6 gate.

I know, the text is a mess. I do have one completely working Soltek SL-54U5 which does have the same AR7010. I will have to use that as a reference and/or do some part-swapping.
That way I could possibly rule out broken parts.

Ah.
My Soltek SL-54U5 has the same AR7010. I measured it (nice square wave on pin8). Swapped it for the suspect bad one. Lo and behold, no square wave, no decent voltage.
Now to find a replacement online. Aliexpress seems to have some.

The AR7010 should arrive this week. Then it occurred to me. As the vccio is 5V instead of 3,3V - where else does it go?
Oh well .... tag ram, cache, northbridge, southbridge ... And most of them are not 5V compliant.
Also, the 5V is probably what originally blew QA1.
The CPU that was on this board is dead, I tested it on another board.
I wonder if the VP3 is pin-compatible with MVP3? I've got a dead soltek MVP3 board. At least the southbridge is the same (VT82C586B)

oh2ftu wrote on 2023-09-13, 16:37:

The AR7010 should arrive this week. Then it occurred to me. As the vccio is 5V instead of 3,3V - where else does it go? Oh well […]
Show full quote

The AR7010 should arrive this week. Then it occurred to me. As the vccio is 5V instead of 3,3V - where else does it go?
Oh well .... tag ram, cache, northbridge, southbridge ... And most of them are not 5V compliant.
Also, the 5V is probably what originally blew QA1.
The CPU that was on this board is dead, I tested it on another board.
I wonder if the VP3 is pin-compatible with MVP3? I've got a dead soltek MVP3 board. At least the southbridge is the same (VT82C586B)

They are very different chipsets as far as features go, but who knows.

These may be of help:
https://dosdays.co.uk/media/via/VIA_82C597.pdf
https://theretroweb.com/chipset/documentation … bc432113548.pdf

.. and I seem to have managed to order the wrong part. Oh well. I'll get back to you in two weeks.

oh2ftu wrote on 2023-09-18, 13:50:

.. and I seem to have managed to order the wrong part. Oh well. I'll get back to you in two weeks.

Or so I thought. The aliexpress seller contacted and told the part is NLA.

Oh bummer. Still looking for an AR7010 SOP-8 pwm chip, any ideas where I could score one?

Check www.utsource.net

utsource had 34k in stock, but after an inquiry they reported that they have none.
"Nice".