How to test 1M0880 FPS?

[mikay786]

Re: How to test 1M0880 FPS?

the top 9 pins of the transformer all have continuity, is that normal?

And is this transformer being fed both AC and DC?

[budm]

Re: How to test 1M0880 FPS?

BTW, you resolder all the components pin on the board, right? Including the OPTO PC911?

[mikay786]

Re: How to test 1M0880 FPS?

yep

[budm]

Re: How to test 1M0880 FPS?

the top 9 pins of the transformer all have continuity, is that normal?

And is this transformer being fed both AC and DC?

That is correct because each output winding has one pin connected to common cold side GND.

[mikay786]

Re: How to test 1M0880 FPS?

tested all rectifier diodes out of circuit and all fine 0.4v one way

[budm]

Re: How to test 1M0880 FPS?

I need to look at the board layout to see what is stopping the drive circuit from from driving the power transformer.
It is an always on power supply so there should be outputs on the cold side.

[mikay786]

Re: How to test 1M0880 FPS?

will the pictures from before suffice?

[mikay786]

Re: How to test 1M0880 FPS?

will the pictures from before suffice?

could it be one of the smaller ics? like TL431K OR transistors C3198 etc

[mikay786]

Re: How to test 1M0880 FPS?

And do you know what FB901 is? this orange thing

[budm]

Re: How to test 1M0880 FPS?

And do you know what FB901 is? this orange thing

It is just a ferrite bead inductor (a piece of wire fed through a ferrite bead).

[RalfE]

Re: How to test 1M0880 FPS?

Hi,
I have also a Loewe I sound where exactly the same thing happened that was described before.

The resin was completely burned away. I am assuming it's meant to keep both resistors appart since they have a high voltage difference.

Now I have soldered in two new R912 and R914.
I meassured them and I thought that they were fine, but I exchanged them anyway.
However, if R912 and R914 get shorted there could be a high voltage at pin 5 of IC901, the 1M0880B.
I have a new one laying on my table right now but before soldering it in, I wanted to double-check the voltages at the different input pins.

Now the problem: I meassure 70V between Pin2 and Pin3 with IC901 removed. The maximum allowed voltage according to the datasheet is 30V. So I am reluctant to put the new one in and fry it.

And I also don't know how that voltage get's there. What is the voltage supposed to be present on C906. It's rated to 450V but my assumption was that the current is first transformed down and not up.

I found the service manual with all the schematics here:https://elektrotanya.com/loewe_indiv.../download.html

[RalfE]

Re: How to test 1M0880 FPS?

I figured it out.

The short between R906 and R912 killed Q911 and damaged IC901.

The way to test the 1M0880 quickly is to give a supply voltage of 20V to pin 2 and 3.
Now pin 4 and 5 should show above 3V. (actually 9V and 5V respectively).
For this you have to remove the M0880.

You can also test the OPTO couplers. They get 12v input voltage at pin 1 and 2.

I would recommend that you replace Q911, IC901 and both optos PC911 and PC912. I don't see how the rest of the components could be damaged by this kind of problem.

Be carefull, C906 get's 350V and keeps the voltage for a while.