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Marantz 2230 Transformer Partially Irresponsive

Warren-Oates

Warren-Oates

One Dim Bulb
Subscriber
I have a Marantz 2230 that I am trying to refurbish. I was told that the unit would not turn on and the previous person had replaced the main fuse and found it still would not turn on. The fuse I found in it looked strange, but tested ok. I put a new one in to be sure. When I powered up under a dbt there was no draw, no sign of life. Somebody had replaced the power switch, perhaps trying to fix the issue, I bypassed the switch and twisted the wires directly together. Still nothing on power up. Next I took my meter and measured ohms at the ac plug, but I cannot get any reading. I have removed the transformer from the chassis, I probed the red and blue wires directly but I cannot get any ohms. I also tested all of the other wires:

Orange Pair (goes to main bridge) .8 ohms
Green Pair (ac feed to lights) .3 ohms
Yellow Pair (AC to power supply board) 12.5 ohms
Black center tap to each Yellow Wire, each way about 6.2 ohms

These measurements are very close to the numbers that AK member Eastpoint had posted in a previous thread about a 2230 transformer, and I think these numbers show the transformer output is fine. From what I understand though there is a thermal fuse inside of the transformer, when the line AC draw is too much it can heat up, then it opens and you have a dead transformer. Is it likely that is what I have hear? Would a likely cause be the main bridge rectifier is shorted?

Beyond that, does anybody know of a thread where getting access to this thermal fuse is discussed, or even better a video?

Transformer_Removed.jpg
 
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That transformer almost certainly has an internal thermal fuse in the primary. They can usually be replaced, but it does require some surgery. The ones I have seen are typically 152 degrees centigrade, which means things got really hot unless it just failed for another reason.
 
I think this is it, I don't know enough to just start cutting up the copper bands. I'll report what I can find out.

20260303_115115.jpg
 
Nice! photo there really helps. I was thinking it had to be unwrapped, but that guy managed to dig it out.

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Found it, it was inside the larger gap, attached is a photo of it being pulled out. I cut one end, loosened it up between the windings with a small flat head screw driver, then pulled on the other end. When installing a new thermal fuse, should I reuse the white insulation? Can I then electrical tape the soldered ends of the
 
Maybe some heat-shrink tubing. (I didn't know if you were asking the question or not?)
 
Be VERY careful when soldering the new one in. Most of the time the originals were put in with a small crimp rather than solder. You can easily "blow" the thermal fuse while soldering it. I use a heatsink on the leads, and spray the body with freeze spray when I solder one in.
 
Nice tip. I just gave the transformer to a friend of mine that has experience building transformers. He's more qualified to repair the fuse, he thinks it can be dug out, looks like it's sandwiched in between two pieces of fiberglass. I will pass on this solder tip right away.
 
My friend will be the one digging it out. I think he may jumper the fuse, and see if he gets 4 ohms on the primary, which should indicate only problem is the fuse.
 
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