Genelec 8020 Repair - Blowing fuse & Dead transformer

[aviel]

Hey,
I got a pair of 8020B and one of them had it's fuse blown away.
I inspected the transformer which has total of 5 wires Blue, Black, Yellow, Yellow, Green.
The resistance between yellow-green pair is 1.6Ohm, while Blue -black is infinite.
I compared this to the other speaker, where i got 108 Ohms between the blue-black.

So the traffo is dead, but i wonder why, and if replacing it wont make it blow out again?
Also, could someone help me figure out what transformer I need?

Thanks!

 

[Whoops]

Hey,
I got a pair of 8020B and one of them had it's fuse blown away.
I inspected the transformer which has total of 5 wires Blue, Black, Yellow, Yellow, Green.
The resistance between yellow-green pair is 1.6Ohm, while Blue -black is infinite.
I compared this to the other speaker, where i got 108 Ohms between the blue-black.

So the traffo is dead, but i wonder why, and if replacing it wont make it blow out again?

You need to replace the transformer and then use a current limiter on the first power up, then you can see if you still have a problem without burning the new transformer.

You can easily build a current limiter with a Light Bulb:
https://studylib.net/doc/18713592/this-workbench-gadget-allows-you-to-connect-a-light-bulb-...
https://www4.picturepush.com/photo/a/10715222/1024/Anonymous/AmpCurrentLimiter1.jpg

Probably there's something shorted in the circuit that burned the transformer.
Did you check the Filter Caps?

remove the PSU and take some photos and show us.
Do you see any bulged electrolytic caps?

Also, could someone help me figure out what transformer I need?

Best way is to contact Genelec and ask for a replacement transformer, they will sell it.

That transformer is thinner than the standard toroid transformers being sold,
so maybe it will be dificult to get an aftermarket one that will fit the limited space available. Best and maybe only option is Genelec

 

[aviel]

You need to replace the transformer and then use a current limiter on the first power up, then you can see if you still have a problem without burning the new transformer.

You can easily build a current limiter with a Light Bulb:
https://studylib.net/doc/18713592/this-workbench-gadget-allows-you-to-connect-a-light-bulb-...
https://www4.picturepush.com/photo/a/10715222/1024/Anonymous/AmpCurrentLimiter1.jpg

Probably there's something shorted in the circuit that burned the transformer.
Did you check the Filter Caps?

remove the PSU and take some photos and show us.
Do you see any bulged electrolytic caps?




Best way is to contact Genelec and ask for a replacement transformer, they will sell it.

That transformer is thinner than the standard toroid transformers being sold,
so maybe it will be dificult to get an aftermarket one that will fit the limited space available. Best and maybe only option is Genelec

Thanks.
A few questions + pictures.
As you can see in the pictures, the pcb looks 100% ok, at least from eye inspection.

1. If the primary is actually open circuit, how come it still blow fuses? I cant understand how come.
2. can i do the light bulb current limiter trick and bypass the fuse?
3. could I theoretically use the traffo of the other speaker, connect it with current limiter (and bypass fuse) to test the PCB? is it safe to bypass the fuse ?

 

[Whoops]

Thanks.
A few questions + pictures.
As you can see in the pictures, the pcb looks 100% ok, at least from eye inspection.

For sure the capacitors don't look to be bulged, at least to the naked eye, although they can still be bad.

1. If the primary is actually open circuit, how come it still blow fuses? I cant understand how come.

Are you sure that it's the Primary that it's open and not the secondary?
can you do a schematic/diagram of the transformer with voltages?

You would have to measure the good transformer to do this

2. can i do the light bulb current limiter trick and bypass the fuse?

You should never bypass the fuse, if there's a short the Light bulb current limiter will limit the current and not allow the fuse to be blown, but always keep the fuse there as a measure of safety

\3. could I theoretically use the traffo of the other speaker, connect it with current limiter (and bypass fuse) to test the PCB? is it safe to bypass the fuse ?

You could do that, but don't bypass the fuse, leave the fuse there. And you have to be really sure that you are really using the Current Limiter otherwise you risk burning a good transformer

 

[aviel]

Thanks.

I will do what you suggested. I dont have any 315mA fuse anymore, and i wanted to proceed on debugging. I am still trying to figure out where I can buy one 0.315A fuse.

 

[radardoug]

Its very common for toroids to have primary shorts, and this always blows fuses.

 

[Whoops]

Its very common for toroids to have primary shorts, and this always blows fuses.

For sure but if Blue-Black is the primary and the DC measurements reads infinite, then it’s open and not shorted.
But maybe there’s a short is some other winding or maybe Blue/Black is not the primary

 

[oldskool1]

I just replaced a transformer in one of my Genelec 1031a's. The primary windings had gone open due to the (internal to the transformer) thermal fuse blowing. The thermal fuse blew because the IEC power cord was loosely connected and I pushed it in while the unit was on, resulting in much on-off-on activity, which was too much for the poor transformer. I won't make that mistake again. Genelec charged $220 for the replacement transformer shipped, and they were very nice. I was able to find an OEM transformer with the same specs, but in the end the Genelec replacement had the correct connectors and mount and was the much easier route.

In your case it should be pretty simple to trace the circuit with a meter from the IEC connector through the fuse to the transformer to find out if it is indeed the primary that is open.

 

[Whoops]

Genelec charged $220 for the replacement transformer shipped, and they were very nice.

That's a ridiculous high price for that transformer, those bastards, they are really overcharging people, that's not very nice at all

 

[oldskool1]

That's a ridiculous high price for that transformer, those bastards, they are really overcharging people, that's not very nice at all

Well, not really. Like I said, I looked around and could have purchased a compatible transformer, but then I would have to source the Molex connectors, get the crimp tool for that size of wire, connect them (there are a lot of wires on those two connectors), fashion a mount that is compatible... all to save less than $100. My time is more valuable than that. Genelec is only slightly overcharging in my opinion, and I don't even think I would call it overcharging... but of course this depends on one's view of how a business works.

 

[radardoug]

Whoops, I think Genelec are to be commended for having spare parts inventory, and there is a cost for them to do it. I am currently trying to source a special transformer for a valve mike power supply. The manufacturer of the transformer is being very helpful, but the manufacturer of the microphone is not. Looks like I will eventually have to do a redesign, which will cost a ot more than if I could get the right transformer. My time is valuable, and you need to factor that in as well.

 

[aviel]

Genelec actualy said that they dont sell parts and sent me to the local distributor to send for repair. I will have to source a third party trafo i think

 

[aviel]

I am trying also to source spare fuse.. the 315mA are hard to find. I assume 300mA will do fine? Or maybe 400mA? The speakers are rated as 20W and im on 240V which implies 288mA.
Also should i use fast blow?

 

[oldskool1]

They don't sell parts? Hmm. Maybe they only sell parts for obsolete designs? Talk to this guy, he was very helpful to me less than a year ago:

Jim Ciardelli
Service Manager
Genelec Inc
508-652-0908

I do think a 300mA fuse will work fine. (edit: I didn't see that the OP mentioned a fast blow fuse. I agree with Brian Roth below, yes a slow blow fuse is needed here.)

 

[Brian Roth]

I would think a slo-blo fuse would be required for ANY mains input...inrush current to charge the capacitors.

 

[Malmi315]

I have the same problem. Replaced with an OEM toroid. There is a flaw on design. The transformer it’s always working cos power switch is after the transformer. So if you don’t use your monitors is good idea to unplug from the power AC.

 

[Malmi315]

Unplug connector from the amplifier board and test output voltages ( ac ) from the transfomer first, to be sure of the problem.

 

[aviel]

I am quite sure this is the traffo since when I swiped the traffo from the other speaker there was no short.

I measured AC and impedance on the good speaker :
Primary - Blue-Black: 108Ohms, 240V (AC)
Secondary - Yellow - Green: 2 Ohms, 18 V (AC). for some reason both yellows gave me 18V with the green, I was expecting one to be -18V, maybe I missed something.

The bad traffo measures same impedance on secondary, but 18 Ohms on primary (10X less).

The official response I got from genelec is that they don't sell parts.
The transformer i have here is roughly 60mm in diameter and 20mm height, which is kind of impossible to source.

 

[aviel]

They don't sell parts? Hmm. Maybe they only sell parts for obsolete designs? Talk to this guy, he was very helpful to me less than a year ago:

Jim Ciardelli
Service Manager
Genelec Inc
508-652-0908

I do think a 300mA fuse will work fine. (edit: I didn't see that the OP mentioned a fast blow fuse. I agree with Brian Roth below, yes a slow blow fuse is needed here.)

do you have his email by any chance?

 

[oldskool1]

do you have his email by any chance?

I reached Jim at
Jim Ciardelli (Support) <[email protected]>