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Robotrontechnik-Forum » Technische Diskussionen » K7222 repair » Themenansicht

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000
09.06.2025, 11:10 Uhr
RetroNora

Hello RT people,

I have an issue with my monitor for A5120.
No surprise that the HV winding of UHA78 is broken.

But it seems that the low voltage side is also broken, with that part of trafo installed the monitor consumes a lot of current - 3,5A. It seems that this part of a transformer has also failed.

I have compared the resistance between the trafro from A5120 monitor and 1715. They both seem to have the same resistance.

Is there any schematics or information about number of windings for the low voltage site of UHA78?

Greetings

Dieser Beitrag wurde am 09.06.2025 um 11:11 Uhr von RetroNora editiert.

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001
09.06.2025, 11:13 Uhr
Rüdiger
Administrator

Zitat:

RetroNora schrieb
But it seems that the low voltage side is also broken,

Are you sure? Damaged primary coil is unusual...
--
Kernel panic: Out of swap space.

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002
09.06.2025, 11:24 Uhr
RetroNora

Well, it seems like it.
With the trafo removed the monitor consumes about 0,5A, I remember that before the HV side burned, when the monitor was working it consumed about 1,6A. Now, it is consuming 3.5A, in fact it wants more, but that is the limit on my bench PSU. The fuse inside that monitor is 4A.

There seems not to be any obvious shorts on the board.

When I was compared A5120 monitor with one from 1715 I have noticed that the resistance between +12V and GND is 37Ohm in A5120 and around 47Ohms in 1715 monitor. Other then this no obvious differences.

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003
09.06.2025, 12:15 Uhr
Rüdiger
Administrator

You get the 3,5A if only primary coil is mounted?
The power transistor beneath the transformer is still alive?
--
Kernel panic: Out of swap space.

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004
09.06.2025, 17:21 Uhr
RetroNora

Yes, the transisor is well.

I get the amperage with only the primary side installed.

I found some pics online of UHA78 with coils only on one side (the one with HV coil).

My unit from A5120 has coil on both side of the ferrite, and I think the site without the HV coil is broken.

I was trying to figure out to what pins of the coil base the windings are connected by looking at this monitor schematics, but it makes no sense for me.

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