FM Towns UX20 Defective CRT Power Board

Started by AmigaDepot, June 20, 2021, 07:09:30 AM

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Good evening.

My FM Towns UX 20 has arrived. The seller had sold it as being defective. Luckily enough, the Towns works fine including sound, mouse and CD drive.

Unfortunately, there is no reaction from the CRT screen. No light and you cannot even feel a static loading of the CRT screen. It also seems that the heating of the tube is not working.

I have changed all the capacitors and under C523, C524 and C525 there was already electrolitic fluid that had leaked from the capacitors. I have cleaned the area with isopropyl alcohol.

The CRT still remains black, as in the first part of this video:

I have noted that JM502 (the black part just above the fuse and left to the power connector) becomes extremely hot within seconds. There might be a short circuit.

I have also noted that voltage arrives on the board and the big capacitor in the front, but there is no voltage in the secondary area (above the colling device).

Does anyone know that that item is. Did anyone have similar problem and might tell, what other parts need to be changed except for the capacitors


All capacitors in the CRT PSU and computer PSU (other vertical positioned card near this one) need to be changed.
Disassemble cd rom drive very carefully. There is some bipolar capacitors that could also be leaking. Your drive might work but you need to check these. My friend with UX20 had his capacitor also leak specifically bipolar ones.

De solder suspect IC and take more photos. Also where was the very heavy leakage? All nearby components are suspect.

I might have extra IC I can give you if it can't be identified


For what it's worth, the Trinitron tube in the all-in-ones appears to be the very same tube used in the Mac Color Classic. Wonder if they share any elements of their analog-board/monitor chassis design.


Thanks to Cyothevile, the UX20 is save.

Indeed it was (luckily enough) the CRT power board. Cyothevile has sent me another board and it works perfectly.

Just replacing the old capacitors on my old board did not fix it and I am no tech expert to find out what it was.