Help identify transformer

Thread Starter

Bassquake

Joined Feb 16, 2018
85
Hello all.

I'm trying to repair a Brother AX-425 typewriter and the power part keeps blowing its fuse, I've narrowed it to the transformer, but I tried searching online on what the transformer is to find a replacement and no luck.

It says on it:
UR0062
AX-B-230V-E-R
TAM K 1034


I've attached screenshots. Any help appreciated.

20180216_153947.jpg 20180216_154206.jpg
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Are you sure it is the transformer and not any part still connected?
Generally transformers show signs of stress after failure, it should not be hard to reverse engineer it.
Looks like a 230v primary?
Max.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
85
Are you sure it is the transformer and not any part still connected?
Generally transformers show signs of stress after failure, it should not be hard to reverse engineer it.
Max.
Hi

Yes, its definitely the transformer, I removed the bridge rectifier that comes after it, and it still blows the fuse. Replaced mains wiring and plug (and fuse), still blows the 250mA fuse on the pcb. Theres literally nothing else left to narrow down to!
 
Last edited by a moderator:

MaxHeadRoom

Joined Jul 18, 2013
28,619
So if it is a 230v primary, what is the LV power components? Is there any indication of secondary voltage and just one or more sec.?
Shouldn't be hard to sub from the likes of Hammond etc.
Max.
 

AlbertHall

Joined Jun 4, 2014
12,345
Hi

Yes, its definitely the transformer, I removed the bridge rectifier that comes after it, and it still blows the fuse. Replaced mains wiring and plug (and fuse), still blows the 250mA fuse on the pcb. Theres literally nothing else left to narrow down to!
The fuse should be a slow blow or anti-surge type. If you use a fast blow fuse it may well blow even with a good transformer. There is an initial surge of current when power is applied to a transformer primary.
 

ebp

Joined Feb 8, 2018
2,332
It was probably custom-made for the product. This is very common in consumer equipment.

The really important thing we need to see is the pins or other photos that give some idea of windings. It is also common for transformers to have two or more secondary windings. For example in a typewriter, one winding might be used to power the logic circuitry and another for the motors.
 

ebp

Joined Feb 8, 2018
2,332
We seem to have two threads on this.

My guess is custom transformer and that there is a shorted turn. Shorted turns can be detected in an out-of-circuit transformer by trying to "ring" the primary with a pulse and looking for fast ring-down (requires suitable pulse source and oscilloscope) or by checking primary current with a low AC voltage applied.
 
Last edited:

AlbertHall

Joined Jun 4, 2014
12,345
Hi

Yes, its definitely the transformer, I removed the bridge rectifier that comes after it, and it still blows the fuse. Replaced mains wiring and plug (and fuse), still blows the 250mA fuse on the pcb. Theres literally nothing else left to narrow down to!
You must use a slow blow or anti-surge fuse. A 'normal' fuse may well be blown by the initial surge when power is applied.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
85
@AlbertHall: The original fuse didnt look like a slow blow, looked exactly like a quickblow which is what Ive been using.

@MaxHeadRoom: Sadly theres no indication of what the DC voltage to the typewriters pcb is supposed to be. I'm testing just the power part, I'm not plugging it in to the typewriters pcb to rule it out.

I do notice that when I use the multimeters continuity checker, it alerts when I try the secondary terminals on the transformer. Is that normal?

Have attached some more pics if any help.
 

Attachments

Thread Starter

Bassquake

Joined Feb 16, 2018
85
@MaxHeadRoom: It says A1757 F 006, attached pic. Have already removed it and fuse still blows. I also removed the bridge rectifier (thin rectangle) which is between the transformer and heatsink so no voltage goes to the dc part at all, still blows.
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
28,619
No Q2?
What I would be inclined to do is draw out the reverse engineered layout schematic, there is only a small No. of components.
Right after the large DC traces from the bridge.
Max.
 
Top