Crate CR-165B amp ?

[gtrplayr1976]

Hey folks,

I'm working on a Crate CR-165B amp for a friend. I've had many issues, but i want to take one at a time. I'll include the schematic for reference.
this issue is with the poweramp/supply. Resistor R21 is burning on powerup. I do not have the preamp/control board connected, and I do not have the board heatsink screwed to chassis. I have replaced about all the transistors on the board except Q3 which checked ok. Diodes have been checked/replaced. C15, and C16 replaced. Any ideas ?
Crate CR-165B.pdf

[Enzo]

Resistors burn up for a reason, it is never their own fault. The reason is excess current flowing through them. That excess current has to come from somewhere, there will be a path for it.

Please do not connect a speaker load to this amp until we have it stable and no DC on its output.

If R21 burns up, then it is very likely a problem with Q7 and/or Q9. And possibly R20 is open. Make sure R27,28 are not open.

R11-14 and the bias control are very important, make sure none of them are open, and see that the bias control works.

And while you are at it, check R18,19 on the bottom half.

[gtrplayr1976]

Resistors burn up for a reason, it is never their own fault. The reason is excess current flowing through them. That excess current has to come from somewhere, there will be a path for it.

Please do not connect a speaker load to this amp until we have it stable and no DC on its output.

If R21 burns up, then it is very likely a problem with Q7 and/or Q9. And possibly R20 is open. Make sure R27,28 are not open.

R11-14 and the bias control are very important, make sure none of them are open, and see that the bias control works.

And while you are at it, check R18,19 on the bottom half.

OK Enzo....thank you.

[gtrplayr1976]

ok....all resistors and bias checked ok. Q9 ..although new..was bad. That has been replaced. To test this should I have both boards mounted, and connected together, or just connect the PS board to transformer, and leave the jumper to the preamp/control board off ?
Thanks for the help.

[Enzo]

I have no reason to want the preamp disconnected. SOmetimes input connections carry a ground connection to the input stage of the power amp and is thus necessary. DOn;t think so here, but no reason to take chances.

When you replace parts, and then fire the amp up and a fuse blows, then never assume the parts you just installed are still good. A bad driver transistor can destroy a new output transistor in an instant. SO you must always recheck even the new parts after a fuse blow.

Look up "light bulb limiter" and make one and use it.

[gtrplayr1976]

Enzo, Could you use a Rheostat instead of a light bulb, and on/off switch ?

Thanks, Tom

[Enzo]

The point of the light bulb is that if the amp is shorted inside the lamp comes on and uses up the power.

It is a light bulb in a socket with two clip wires. I can't imagine anything simpler or cheaper.


Yes, I can use a variac with current meter and a lot of caution, but I run a pro shop. The bulb trick will save you a lot of parts.

[gtrplayr1976]

Sounds like a plan. I'll give it a try. Thanks Enzo.

[gtrplayr1976]

Ok Enzo.....where do I connect this light bulb limiter ?

Thanks, Tom

[Enzo]

If you read the web pages associated with the limiter - and many people have written about them - there should be discussion of its use. It is connected in SERIES with the AC power mains.

[gtrplayr1976]

I found it Enzo...thank you.

[gtrplayr1976]

Ok Enzo..I finally made the limiter. I have a 25 watt bulb in the circuit. I plugged it all in ,and turned on the power. The lamp was bright for a second, and is now very dim. So far nothing has blown. Most voltages I'm seeing are 26.5 to -26.5 DC, but it's kind of hard to find some of the TPs from the backside of the PS board. I will take a closer look if there's something in particular I should check ? I'm reading with the negative to chassis ground.

Thank you, Tom

[dorrisant]

Would someone be so kind as to repost a schematic for the CR-165B... The link above in the original post is dead.

Thanks in advance!

Tony

[nickb]

Here ya go bud http://bmamps.com/Schematics/crate/C...Schematics.pdf

[gtrplayr1976]

Would someone be so kind as to repost a schematic for the CR-165B... The link above in the original post is dead.

Thanks in advance!

Tony

I need to dig mine out ,and try to fix it again