I’ve had a REL T/9i in use for 5-6 years and always kept it on. Recently it blew a fuse. I disconnected it from line source and replaced the fuse, only to blow again and again when turning it on. Sent the plate amp to REL, which tested good. Tested the driver which is also good. The remaining culprit is the transformer, which REL is going to source for me with a fee of course.
I understand it is rare that a toroidal transformer would fail, especially one that had been working flawlessly for years. Anybody have this kind of failure before? Any thoughts on how to safely test the transformer? Other thoughts?
From your description it sounds as if the transformer is mounted separately. A transformer drawing excessive current indicates a short. Very unlikely that it is within the windings. Visually inspect any board solder connections of leads or connections to plugs. Energise the speaker without the amp but with the transformer. Then do the same with it connected to the amp board. If it only blows the fuse when connected and REL says the amp board is OK then the physical stress of connection the transformer to the amp board may be causing a short.
There may also be an issue with any inrush limiting devices. When you first apply AC power to the unit there is likely a capacitor (or capacitors) that filter the rectified AC. This results in a very large current initially when powering up as this capacitance briefly looks like a short circuit.
Not familiar with this specific subwoofer, but if that toroid has any components at its input that could be the issue.
Best of luck and please let us know what you find.
Kurt
Thanks for the responses, I’ll do some further investigating. As far as I can see the plate amp contains all components and solder joints. The transformer is completely separated and only has leads for input and out put. The plate amp has all the other filtering etc on it. The REL engineer says he has fully bench tested the plate amp and it has been running for 48 hours with no problems. I still have trouble believing that a transformer (just windings) has failed. Wonder if there is a continuity test I can run with a multimeter (ohms) that could reveal a short.
A cursory web search reveals that a toroidal transformer most likely fails if the center bolt has been over tightened which could cause a physical fracture in the windings. I guess that is possible, however the bolt was tightened at the factory 6 years ago and just now caused a fault?
Perhaps someone knows if these continuity results mean anything. Pictures show transformer configuration.
Input side continuity:
Brown & Blue
Orange & Brown
Orange & Blue
Black & White
(no continuity between input and output leads)
output side continuity:
Black & Blue
Black & Red
Red & Red
Blue & Blue
If it was me troubleshooting this, I would just hook up the primary to the 120 V and leave the secondaries disconnected.
I assume the fuse is in line with the primary and it will blow if there’s a short in a transformer.
That is a great suggestion! I was so convinced early on that the plate amp was at fault I didn’t trouble shoot anything else. The plate amp is with REL with the integrated switch and fuse, but I could rig up a fused IEC and try that out. Thanks for the tip.
Since the fuse that blows is on the secondary side of the transformer, it is unlikely that the transformer itself is bad.
Looking at the picture of your transformer, it appears that it has a built-in primary fuse.
To prove that the transformer does not have a gross defect I would measure AC voltages on the secondaries.
With 120 Volts on the primary there should be approximately 57 Volts and 33 Volts on the two secondaries.
If you measure reasonably close to those numbers I would assume the transformer is good.
Of course, the manufacturer should know their product better than we do so maybe it is the transformer?
I agree with st50maint and still lean towards something “mechanical” like, just a wild thought, a short on the output side of the amp board present only when everything is connected. I can only hope REL is testing the board with a load. Short a class D and you wish the fuse blows.
That “built in fuse” in the toroid could be an inrush limiting device or NTC (negative temperature coefficient) thermistor. These devices have higher resistance when “cold” and when current flows through them they heat up and the resistance drops.
You might try measuring the primary winding resistance and compare with a datasheet or spec for the transformer if you can find one.
Another possibility is that device is an overtemperature protection feature (think thermostat). Not sure how that would lead to fuse clearing though.
Toroid interwinding shorts are not that unusual so if the fuse in on the primary side it could still be an issue.
Good luck.
Thanks to all for the education and tips. I don’t know of another place that has such active and knowledgeable participants. The plate amp is with REL at the moment. I believe REL is sending it back along with a new transformer. I’ll update this post with results when I can. I may end up having to continue troubleshooting after the parts arrive as I am still suspicious of the plate amp.
