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Gallien-Krueger 1001RB-II no power to speakers but direct out works ??

Started by Zappacat, June 04, 2010, 03:01:48 PM

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Zappacat

Gallien-Krueger 1001RB-II : A friend of mine was playing this amp the other night and suddenly he lost all power to his speakers but the direct out was still working.  He continued to play it, no smoke.  I hooked it up and get the same thing.  

My first step in troubleshooting it is to test the toroidal power supply and see if it's working.

The second picture shows a group a wires that come from the transformer and attach to the main board via spade connectors at the far edge of the board.  I haven't been able to test the voltages on these yet.  I assume these are to power the preamp and stuff like that.

The third picture shows group of secondary wires going to what I presume is the power section.  These wires are connected to a modular plug terminal that connects to the plug in between the big capacitors.  The voltages I'm getting off of these wires with the power on can only be measured in millivolts.  Does the plug need to be plugged into the board in order to read the voltages properly or can I just disconnect it from between those big caps and get accurate readings?

Will a continuity test between ANY of these wires and the transformer primary tell me if the transformer is any good?

The following information is taken directly from the power supply label as seen in the pictures :

Input AC:
0-100V-110V-120V
(BRN)RED-ORG-YEL-GRN

0-100V-120V ~50/60Hz
BLE-GRY-VIO

Does 0 in these specs indicate gound?
Why are there two input specs with only one having the ~50/60Hz designation?
What does (BRN) mean?

Output AC:
40.2V 7.74A RED-RED
40.2V 7.74A YEL-YEL
29.9V-0-29.9V 6.44A ORG-BLK-ORG

Assuming the power transformer is on and functioning properly I should be able to hook up my voltmeter and measure :

40.2V AC with one probe on red and the other grounded to what?
29.9V with one probe on orange and the other on orange
approximately 15V with one probe on orange and the other on black

Am I on the right track here?

Thanks in advance.
I put my pants on just like the rest of you - one leg at a time. Except, once my pants are on, I make gold records.

Enzo

While they do fail once in a while, transformers are the LAST thing on the suspect list.  If power is missing to the power amp, it is way more likely to be an open fuse, a broken solder connection, and open resistor, etc.

The direct out works?  In BOTH pre and post settings?   That means preamp is OK.

Is signal present on the master volume control?  and on its wiper?  Is it getting to the power amp board?  Is there signal on pin 1 of the PA input connector?  Is there signal on R19 on the power amp?

I assume we have tried different speakers and speaker cords.

Is there ANY sound in the speakers?  Any little thump or pop at power on/off?  ANd little background hum or noise, or other sign of life?

Is there V+ and V- on the collectors of the power transistors?

Zappacat

I've been trying to find a schematic for this.  Requested it from GK 2 days ago.  Still no response.  Do you have the schematic?
I put my pants on just like the rest of you - one leg at a time. Except, once my pants are on, I make gold records.

J M Fahey

From the pictures (plus the transformer data) I guess it's a complex Class H (or F or G, take your pick) amplifier, with dual-tier voltage rails, probably around +/-40V and +/-90V or thereabouts, truly a beast.
I would not like to have that on my bench without all the servicing backup possible and then some.

Enzo

Yes it is a complex amp, but when the problem is NO sound, I think there is a lot of checking that can be done without the prints.

Jack1962

Indeed you can check a ton of stuff without a diagram on this amp , and perhaps get lucky and find the problem. I would start from signal input to the driver and power section of this amp. chances are if you have power to the preamp and it is functional , your power tranformer is fine. my advise on this one is don't waste alot of time on it until you get the diagrams and any service documentation your can obtain.


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