VintageKustom.com: Repairing Kustom Amps » Need help with Commander power section

Home » VintageKustom.com » Repairing Kustom Amps » Need help with Commander power section

Show: Today's Messages :: Show Polls :: Message Navigator

Need help with Commander power section [message #19113]

Tue, 13 August 2013 13:03

Ted M
Messages: 5
Registered: August 2013
Location: RI

Junior Member

I have a Kustom commander that I would like to get going.

It has blown output transistors, a blown rectifier, and a blown fuse.

While looking over the schematic posted here https://docs.google.com/a/olenik.com/file/d/0B1FxxpOmGO8vWVY 4bVplTTVVZ3M/preview?pli=1&rm=demo

I noticed some dependencies between the schematic and parts layout.

Are R22 and R24 mixed up with R23 and R21 in the layout drawing?

That would seem to be the case when comparing my amp to the drawing. Has any one else noticed this, or was my amp assembled incorrectly? These are the big cement resistors next to the drivers. Mine are labeled .51 10% 5 watt. When I measure them in circuit, I'm getting 1.4 ohms. Ad these to the list?

I'm sure I'll have other questions as I make a list of parts needed.

Report message to a moderator

Re: Need help with Commander power section [message #19115 is a reply to message #19113]

Tue, 13 August 2013 13:35

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I never really noticed that before, but you're right the part numbers are wrong/mixed. I don't really look at the layout drawings that often though.

When you touch the two meter leads together what reading do you get? The resistors may be off value, but meter lead resistance is probably a big part of that.

Report message to a moderator

Re: Need help with Commander power section [message #19118 is a reply to message #19115]

Tue, 13 August 2013 13:56

Ted M
Messages: 5
Registered: August 2013
Location: RI

Junior Member

Hmmm, 1 ohm. So the .51 watt resistors are probably OK? My new ratshak .47 ohm also read 1.4-5 ohms.

I have NOS RCA 4009 and 4010 drivers. ratshak 2n3055's. and a 25amp 50 volt bridge rectifier.

I'm not super experienced fixing amp but know the basics of safety and have been studying up on some old posts related to fixing these circuits.

I'm sure I'll have more questions as I start getting into it more.

Report message to a moderator

Re: Need help with Commander power section [message #19119 is a reply to message #19113]

Tue, 13 August 2013 15:00

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Yes, it would seem that the emitter resistors are okay. Test every transistor on the board and every diode as well.

Watch out for the diode that mounts to the heatsink, the leads can be very brittle and will break off right at the case if you are not careful or lucky for that matter.

The only part that I would have a problem with is the rectifier bridge, 25 amps is way high, but okay, the 50 volts is a little too close for me. I'd rather see a 100 volt part there, but the 50 will work. Are you sure the original one is dead? I really don't see them go bad that often.

Report message to a moderator

Re: Need help with Commander power section [message #19122 is a reply to message #19118]

Tue, 13 August 2013 15:12

Ted M
Messages: 5
Registered: August 2013
Location: RI

Junior Member

Ok, after reading some posts here, I unhooked the red and green wires from the filter caps (taped the ends), and powered up the amp with a 1/2 amp fuse. The Fuse held.

So, the rectifier is not burned out after all? I had inconsistent readings testing it in circuit.

Can I hook the caps back up, and start the amp with the 3055's unplugged to see if the fuse holds?

Report message to a moderator

Re: Need help with Commander power section [message #19124 is a reply to message #19113]

Tue, 13 August 2013 16:12

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Which red and green wires did you remove from the caps, the ones to the circuit or the ones to the choke?

If the rectifier, choke and filter caps were hooked up and the fuse did not blow, then the power supply would seem to be okay.

You can run the power amp without the outputs, but don't connect the speaker or you may damage the drivers.

Report message to a moderator

Re: Need help with Commander power section [message #19126 is a reply to message #19124]

Tue, 13 August 2013 16:20

Ted M
Messages: 5
Registered: August 2013
Location: RI

Junior Member

I removed both sides (the dual wire and single wire) from both red and green.

Should I do this test again with the transformer to caps connected but the PS board disconnected?

Ok I did the test with the choke connected to the filter caps, and the power board disconnected, .5 amp fuse held.

From testing in circuit, think maybe just one of the outputs is blown. If I power it up with the 3055's unplugged, the caps connected to the power board and the fuse doesn't blow, can I assume the rest of the board is ok?

[Updated on: Tue, 13 August 2013 16:30]

Report message to a moderator

Re: Need help with Commander power section [message #19127 is a reply to message #19113]

Tue, 13 August 2013 16:27

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

That would be the next test to see that the filter caps are okay and that you getting the normal + & -40 vdc from the power supply. You can also test the ac voltage on each of the filter caps to see how much ripple there is.

A 1/2 amp fuse may or may not hold with this test, as the caps may initially draw a pretty good surge.

Report message to a moderator

Re: Need help with Commander power section [message #19129 is a reply to message #19113]

Tue, 13 August 2013 16:49

Ted M
Messages: 5
Registered: August 2013
Location: RI

Junior Member

I think I updated my post while you where replying.

I tested the rectifier hooked to the caps and choke, fuse held.

Report message to a moderator

Re: Need help with Commander power section [message #19130 is a reply to message #19129]

Tue, 13 August 2013 17:05

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I personally never assume that there is no other problem when an output shorts, because maybe 60-80% of the time there are other things damaged on the board, typically the drivers.

Why not test the rest of the transistors on the board?

Report message to a moderator

Previous Topic:	severe reverb problem on K100 model 2
Next Topic:	Investigating Kustom 2 Valve Problem

Goto Forum:

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sat Apr #d 11:19:55 EDT 2024

.:: Contact :: Home ::.