Icom: Icom PS125 power supply Issue

[electricuser]

Hello everybody

Can you advise me what parts I should check, measure? Visually, this product has not been repaired, and optically, there was no visible damage or burnt parts.
The device does not work at all. The original R2 has infinite resistance, so it is already damaged, so I tried to measure it with a digital multimeter, where it is and what kind of problem it is when the device is plugged in and turned on.
Q1 had one G contact not properly soldered to the board. So I fixed it. But it didn't help.
When I attached the multimeter test leads and wanted to measure the voltage on Q1, T2 and G, the whole device started up, and the output was already about 14V, but I could also hear a regular, slightly audible crackling sound, something was damaged, maybe there was a short somewhere. I turned off the device after a few seconds. When I turned off the main switch on the PS125 and turned it back on, it was not malfunctioning again. I took out Q1 and measured it with a multimeter, the triac is functional. 2 times it has almost 0 Ohnov and when I turn the multimeter test leads, the resistance is infinite. So I put a new resistor R2. Right after turning on the switch on the PS125, R2 was fired, and infinite resistance appeared, and the device will not turn on. However, when I repeat it by attaching the multimeter test leads to Q1 on the T2 and G contacts, the multimeter will probably turn it on and the PS125 is working. But you can hear a slight crack. I took it out and measured the following parts and they are all fine.
R1 , R3 ,R24
C1..5 , C11,C19,24,25,31..36
D21 ,D22,24,26
Q1,Q2,14
ZNR

The device broke down under another owner, so I don't know why it's not working.
But it's clear it hasn't been fixed yet.,It is clean, not dusty.
I don't see anyone soldering or replacing any parts.
There are still a few capacitors left, but no Elko.
Please can you advise how to proceed?

 

[merlin]

You really should use a scope diagnosing these sort of supplies. DC voltage, take care, you can have 300 volts on the bulk caps and discharge before poking fingers in there.
In this circuit, after the bulk, you have a boost/buck converter that uses a control IC in a feedback. No output there, you have a failure in the converter. After the converter there are rectifiers, and filter circuits. Sadly, my schematic doesn't show voltages or waveforms.
R2 is 6.? ohm that is fusable, check that. D1 is the full wave bridge rectifier, you should check the AC on the inputs. This is a high frequency.
The outputs should be - and + about 13 volts. that feeds the filters for the output.
Seems these are good for 25 amp.
Now, If you are up to a challenge, you can modify a server PSU, for 13.8 volt, and replace the internals. The 450 watt will give you 30 amp.
I use a 750 watt that runs my whole radio setup. 50 amp.

 

[electricuser]

Merlin Thanks for the reply and good advice.

I meant the total output from the device, the final voltage is correct.

R2 has a resistance of 6.8 ohms and is always destroyed when the device is turned on, and then has infinite resistance.
I don't know what other component is damaged, so I'm looking for help online.
I also found a schematic, and there are no voltages there that the device should have when it is fully functional.
If I connect the multimeter test leads to Q1 and want to measure voltage, the device turns on, but I also hear a soft, rapid, and regular popping sound, somewhere in the other part of the device, but I don't smell anything.

Something is wrong because the device cannot be turned on normally and after every replacement of R2 with a new one, immediately after turning on the switch on the device, R2 is irreversibly damaged.

 

[electricuser]

Is it normal if there is an AC input voltage between positions 1 and 2 ?
There should be a resistor R2 there, which is completely destroyed every time the switch is turned on.
I tried turning on the device without R2, there was an input AC voltage of 235V. Suddenly I attached the multimeter measuring cables to measure the voltage of Q1, that is, TM1641S-L between T1 and G, so the device turns on, and at that moment there is no voltage between position 1 and 2, that is, where R2 6.8 Ohm should be connected.
I removed from the board Q1 TM1641S-L again and measured the contact resistance with a multimeter, and the contact is just about zero between T1 and G in both directions, between the other contacts in any direction the contact resistance is infinite.

Triac TM1641S-L when everything is connected on the board, including R2
I measured these values with the device turned off:
between T1 and G 36 Ohms
between T1 and T2 7 Ohms


The only thing I'm not sure about is the value of D9 when the HZ4A2 Zener diode was removed from the board. It had a transition of 0.7 but in the opposite direction it was 2.8. Is this okay?

 

[merlin]

First, if R2 is blowing with no load, you have a short in the filter chain, possibly LF 1, 2, or 3.
C4 or C5 can short also, they have to filter the high frequency and big electrolytics don't play well there.
Q1(triac) is part of the current sense, feeds back to the converter transformer. So, if R2 blows, the converter shuts down.