Hi,
TL;DR: Amp is dead. Protection blinking and relay won't click. What to do?
I've got a Uher MA200 Reference No. 1 and tried to drive a Eminence Kappa-15LF with it, which is part of a big subwoofer. First I used only one channel and as the Uher has a meter, I turned it up to about 200 watts. The sound was awesome, no disortion or clipping but suddenly the fuse burned out (rated 4A/250V). The heatsink was fairly warm but the temp protection didn't kick in.
Instead, the protection led was blinking and the relay didn't click. I opened it up, measured the STK4048V and it was dead. Strange in my opinion, because I watched the powermeter the whole time and the amp has seen worse in its life...
When I unsoldered the power supply of the dead STK4048V, the protection turned off, the relay clicked and the other channel was working again. I bought a new STK4048V and soldered it in. The unit was back to life and both channels were working normally again.
The plan was to use both channels for the Eminence in bridged mode. I built a simple lowpass board which puts out normal and inverted signal. With both signals connected to the corresponding channels and the driver connected to the positive sides of each channel I played some music. The sound was good again, no dissortion or anything... As the powermeter wasn't accurate anymore, because the impendance would split to 4 Ohms on each channel, I only turned it up till it displayed approximately 80 Watts on each channel. The heatsinks didn't get hot, only warm but still, after some time the Uher stopped working again and went into protection mode.
I thought it would be one of the amps again. So I measured each pin of the two STK4048Vs and noticed on the same channel as before, the voltage was to high on some pins. So I unsoldered the supplypins (12 and 14 of the STK) again, as I did the first time, but the protection won't turn of. The other channel seems fine, at least measuring the individual pins showed to be the same as described in the schematics.
As I'm not that good in analog circuits, I'm stranded here.
Can someone help me out here?
I attached the schematics.
Thanks in advance!
Best,
Bene
TL;DR: Amp is dead. Protection blinking and relay won't click. What to do?
I've got a Uher MA200 Reference No. 1 and tried to drive a Eminence Kappa-15LF with it, which is part of a big subwoofer. First I used only one channel and as the Uher has a meter, I turned it up to about 200 watts. The sound was awesome, no disortion or clipping but suddenly the fuse burned out (rated 4A/250V). The heatsink was fairly warm but the temp protection didn't kick in.
Instead, the protection led was blinking and the relay didn't click. I opened it up, measured the STK4048V and it was dead. Strange in my opinion, because I watched the powermeter the whole time and the amp has seen worse in its life...
When I unsoldered the power supply of the dead STK4048V, the protection turned off, the relay clicked and the other channel was working again. I bought a new STK4048V and soldered it in. The unit was back to life and both channels were working normally again.
The plan was to use both channels for the Eminence in bridged mode. I built a simple lowpass board which puts out normal and inverted signal. With both signals connected to the corresponding channels and the driver connected to the positive sides of each channel I played some music. The sound was good again, no dissortion or anything... As the powermeter wasn't accurate anymore, because the impendance would split to 4 Ohms on each channel, I only turned it up till it displayed approximately 80 Watts on each channel. The heatsinks didn't get hot, only warm but still, after some time the Uher stopped working again and went into protection mode.
I thought it would be one of the amps again. So I measured each pin of the two STK4048Vs and noticed on the same channel as before, the voltage was to high on some pins. So I unsoldered the supplypins (12 and 14 of the STK) again, as I did the first time, but the protection won't turn of. The other channel seems fine, at least measuring the individual pins showed to be the same as described in the schematics.
As I'm not that good in analog circuits, I'm stranded here.
Can someone help me out here?
I attached the schematics.
Thanks in advance!
Best,
Bene
Attachments
Looks like the output transistors in the old STK finally gave in to secondary breakdown. SOA on these hybrids isn't too great, and this particular part is recommended for +/- 60 V and operated on almost +/-80 V here (fairly close to the limit of +/-87 V). They really should have used the 4050 the schematic calls for.
You may want to crack open both the old and the new one. I bet the new one shows lesser-quality internal construction, as what you get these days is usually fakes.
Not sure why it still won't come out of protection with power to the dead hybrid removed though.
You may want to crack open both the old and the new one. I bet the new one shows lesser-quality internal construction, as what you get these days is usually fakes.
Not sure why it still won't come out of protection with power to the dead hybrid removed though.
You were right.
I opened up both of the ICs and the new one is definitively of lower quality.
And you were also right about the circuit offering to much voltage. The original ones are actually the STK4050V not the 4048, I don't know why, but I just ordered the wrong ones...
I completely unsoldered the IC and the unit works again. The right one is on its way now.
I opened up both of the ICs and the new one is definitively of lower quality.
And you were also right about the circuit offering to much voltage. The original ones are actually the STK4050V not the 4048, I don't know why, but I just ordered the wrong ones...
I completely unsoldered the IC and the unit works again. The right one is on its way now.
- Status
- Not open for further replies.