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SOHA I Problem

post #1 of 8
1/3/10 at 8:16am
Thread Starter 
Hi,

i cased up and rewired my SOHA I, when i turn it on VR1 becomes very hot and i messure 20V at the 12V testpoint. I have built in the 15V version because i also use jisbos. is the vr1 reg broken or does something else on the bord cause the extreme heat of the vr1?
i could try to build in another vr1 but im not sure if it helps. the vr1 was already broken before maybe they become too hot..
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post #2 of 8
1/3/10 at 8:58am
VR1 =12V Fixed Regulator 78L12
So it would not be higher than too much than 12V unless you connect the pins wrongly.
Try to take a look the pins definition on the datasheet and also see clearly how people place the 78L12 from the following pics.

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post #3 of 8
1/3/10 at 9:03am

Here is my modified SOHA VR1 and VR2.
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post #4 of 8
1/3/10 at 9:28am
Thread Starter 
ive tried to replace vr1 with a 12v model and extra cooling but it still gets crazy hot, something must be wrong on my board..

but im quite sure its not the vr1 this time. do you have an idea what can cause the extreme heat on vr1? its only vr1 not vr2
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post #5 of 8
1/3/10 at 9:28am
I had this problem and there was a short on the PCB, the PCB's were of poor quality with a lot of shorts to the ground plane found. If you shine a light under the board you might find it and cut it out.
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post #6 of 8
1/3/10 at 11:00pm
This sounds very similar to the symptom I had when I had the power transformer wired wrong. I forgot to connect the center tap to ground, and ended up with double the voltage on one side (VR1?) and almost nothing out of VR2. That meant that VR1 would have had to dissipate almost twice the voltage (as heat) that it should have had to normally. Fortunately it didn't hurt anything.
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post #7 of 8
1/4/10 at 4:44am
Thread Starter 
well the pcb is rly in a bad condition since it was my first self-built amp ever. i will get a new pcb and then rebuild the soha completely in a clean way.

thx for ur help anyway, this was a last try to rescue the old pcb^^
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post #8 of 8
1/4/10 at 12:08pm
I was able to salvage mine by checking for shorts on the VR1 output lines and cut the ground plan stray thread.
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