BOSOZ Problem

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vdi_nenna

vdi_nenna

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Joined 2000
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No Good!

I rebuilt the regulators. I got them working with a 2 amp slo-blo fuse. The 750 ohm 1/2 watt resistor got smoked. I switched to 15k and the voltages were fine. I got 58v-+. Plugged it into the main circuit and I watched a spark fly from one of the FET on the regulator board.

At this point, even if it did work, I wouldn't trust to leave it on while I'm out of the room. I just don't trust it.

This circuit will have to live without regulator boards. It sounds real good without them. It leaves me to wonder what it would sound like with the reg board, but somethings are better left untouched.

Raoul, I'd buy that reg board from you, but I'm afraid it will be the same story. Thanks! I'm going to make a nice filtered, unregulated power supply, and try to be happy with it.:(

thanks,

Vince
 
R

Raoul

Member
Joined 2003
Hi Vince,

I actually wasn't concerned with compensation for the board, but I understand if you don't feel that you can trust the thing alone in a room. I also have a few of those FETs (or at least the IRF510/9510) sitting in bins. I haven't been using them very quickly, so if you ever need a few I could toss some in an envelope.

Good luck with the unregulated supply.

ps. Do you have any way of taking a few pic's of the psu and main board and the connections?
 
R

Raoul

Member
Joined 2003
Email sent. I had a little time this evening, so I tested the PS board with my working mainboard and the same transformers that you purchased from ApexJr (good deal, BTW). Everything checked out fine. Q101 and Q102 Drain checked out at about 83V+/-, Source at just over 60V+/-.
 
vdi_nenna

vdi_nenna

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Joined 2000
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I guess you are saying I should have used a 5 watt or better?
I didn't calculate the disipation. Lazy, novice mistake.

I don't know how much difference it makes, but the FET burned on the + side; not on the - side where I used the 750 ohm resistor. It didn't burn when 15k was in place.
 
R

Raoul

Member
Joined 2003
I think that you should be fine with a 15Kohm 1/4w resistor on both the positive and negative side, driving to ground.

(from page 7 of 9, BZLS manual .pdf posted at www.passdiy.com)

"It is possible to test the power supply board without the main board. Simply load the V+ with 15Kohms 1/4watt to ground and the V - 15Kohm to ground and look for the 80 volt values on the plus and minus rails and the 60 volt values on the plus and minus regulated rails."

So you are on the right track with your original testing, methinks.
 
vdi_nenna

vdi_nenna

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Joined 2000
Paid Member
Hi Guys,

I got back around to trying to repair the regulated PS for the BOSOZ. I rebuild the PS with a few new FETS, Caps and bridges.
The negative side gets -58v and the positive side is at 0.

After the large caps on the PS board, there's about +86v on the negative and positive rail. At R101 (4.75k 1/4w), there is about +86v, but after R101 on the + rail I get no voltage. I replaced the resistor with a 2w 4.73k resistor and I get the same thing- 0 volts. The negative side shows 61v after R102.

Voltage across R101 is 86v. Voltage across R102 is 24v.

Any idea what this problem is?

Thanks,

Vince
 
B

BDP

Member
Joined 2002
Check your string of zener diodes. With the power off check the resistance of the zener string to ground. If its a short try lifting one lead in the string to open the circuit. You should then get a capacitance multipier with the output of the regulator 4 volts less than the input. Use a dummy load so you don't ruin your preamp while testing.

BDP
 
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