Repair attempt Analogic AN3100

[pyroesp]

I've bought a AN3100 which should have een working. Turns out it doesn't.
Long story short, I still have it and want to repair it.

I've set the switch to 230VAC, plugged it in and ... nothing.
I have voltage at the primary of the transformer but not at the secondary, so I thought maybe something is overloading the transformer. Although nothing got hot I hoped it wasn't an issue with the transformer itself.
Anyways, I desoldered the 4 diode rectifiers, they where all fine. The only thing still connected to the transformer was a heating resistor inside the zener reference HR1 or CR11.
I disconnected one of the outputs of the secondary, and then measured again, but no luck.

After some more troubleshooting of the 230V/120V switch and transformer, I'm left with a transformer who has no continuity between 1 en 2.
I'm hoping this has some sort of a fuse which is open.

My question is, how can I see if this transformer has a fuse. If it does, how troublesome will it be to try to bypass (or replace if possible) the fuse.
If not, does anyone know of a replacement part for this ? I'm going to search on mouser.

Primary side has 5 pins, 5th one being earth. Secondary has 3 pins for 2x17VAC 1x17VAC and 1x7VAC @ 0.4A each (looking at the schematic).
5th pin isn't needed, I can just add an earth cable to the transformer.

Here's a link to the manual with schematic and parts list: http://uebergabe-daten.hifi-classic.at/httpdocs/BDA_SM_Archiv/Analogic/Analogic_AN3100_MES_BDA.pdf

PS: Part number of transformer is Analogic 15-151049 rev 4A

[ManateeMafia]

I have an AN3100 that had bad CR1 and CR2 diodes but no problems with the transformer.

If there is an internal fuse, then most likely the windings shorted and it is not worth the effort to tear it apart if possible.
The drawing shows the secondaries as being 17V each but the linked service manual states that one is 17VAC and the other is 7VAC. This will need to be confirmed before looking for a replacement.

You can always use an external transformer, if necessary, and add an external power connector.

[pyroesp]

When measuring ohms on 1 and 2 I get overload, and in diode mode I get nothing.
Ohms measurement between 3 and 4 gives me 145Ohms.

The only transformers I currently have are two 230VAC to 1x12VAC @ 1.5VA (127313 from block-trafo) which are for another project. They're similar to this : http://uk.farnell.com/block/vb1-5-2-12/transformer-1-5va-2-x-12v/dp/1131624

The drawing shows the secondaries as being 17V each but the linked service manual states that one is 17VAC and the other is 7VAC. This will need to be confirmed before looking for a replacement.

That explains why I have 2 different ohms measurement at the secondary.

Only thing I can do is search for a replacement. I need the 24VAC for the heater and the 17VAC for the + and - 15VDC.

EDIT: Just opened the first few paper layers with a hot air gun and xacto knife and didn't see a fuse or break. The wire goes into the transformer after that, so I'd have to completely open it to seach for a break, which I'm not really willing to do right now.

[singapol]

You should check the specs in the service manual of the 17V transformer current rating.Is it 0.4A for 2X17 which would mean 0.2A for each 17 coil or 0.4 per coil. So the VA or power rating will be 17 X 0.4= 6.8VA. The problem is off the shelf transformers at 17V are not common. The next common one would be 18V so for +/-15V you need one that is 2x18V say at 10VA, a lttle extra for power loss and get another 24V trans. but you have to check what current the heaters are drawing and add at least 10-20% for loss. Another alternative is to custom wind your transformer if there is a winder near your location where you are.

[pyroesp]

It's actually 1x17VAC + 1x7VAC to make a 24VAC for the heater at the zener, which will be even less common if not impossible to find.
Both windings are rated, on the schematic, at 0.4A.

Edited the first post to avoid confusion.

[oldway]

As the primary of your transformer is open and not short circuited, you can use this transformer as an auto transformer to obtain 17V + 7V from an external 24Vac.
Only supply the secundaries 17+7V by 24Vac.
You can use for exemple an external EREA transformer E32TR10 or E32TR16.

[EPTech]

The autotransformer is a good idea.

Another idea could be to just use a transformer with 24VAC secondary. Supply the heater with that, rectify the 24VAC and put a 15V regulator on the positive rail to supply the circuit.

Happy repairing.

[pyroesp]

The autotransformer idea is great.

A friend of mine has a 230V to 6-12-18-24VAC @ 1A, which should work nicely with the AN3100.
Only downside is that it's single input.

I'll see if I can get a dual input primary to 24VAC, but in the meantime this should work.

[carl_lab]

It's actually 1x17VAC + 1x7VAC...

Which is the 7VAC and which the 17VAC?

[pyroesp]

From the schematic it looks like pin 6 and 7 from the secondary is used for 17VAC. + and - 15VDC is derived from the 17VAC.
Pins 7 and 8 are for 7VAC, which does not seem to be used to generate a DC voltage.
The additional 7VAC is to make 24VAC between 6 and 8 for the heater element in HR1.

[EPTech]

Hi There,

I have studied the schematic more closely and came to the conclusion that my previous suggestion would be completely useless to you. I assumed the opamps were single supply but they are not.  I am sorry for that.

[pyroesp]

I have studied the schematic more closely and came to the conclusion that my previous suggestion would be completely useless to you. I assumed the opamps were single supply but they are not.  I am sorry for that.

No worries, I'm glad you're helping.
I actually thought about doing that on the positive and negative supply.
But the thing is that it regulates it's own 15VDC (pos & neg) and I would have to either bypass the regulation or find a way to make the 15V regulator send 1 or 2V more to compensate for voltage drops in the regulation circuit.

I'm worrying a bit about just using a 24VAC transformer as there would be a large voltage drop across the input and output of the regulation circuit.
That's why I'm going to use a 6-12-18-24VAC.

I can't seem to find a transformer 18-24VAC on mouser/digikey... Should I trust Chinese transfomers ?