Crate problem

[Valvehead]

I have a GLX65 Crate combo that doesnt want to switch to the "Solo" channel. I cant find a schematic for it-wondering if anyone here has been inside one.

I checked the push button switch, its ok.

Ive cleaned and re-flowed the footswitch jack .

Ive also moved the ribbon cables around with the amp on. Still cant make it switch .

any experience with these?

[Enzo]

Did you measure the resistance between contacts and cutouts on the FS jack? The parts that touch the FS plug don't matter, it is the side contacts that open when the plug goes in that matter. DOn't rely on cleaning, MEASURE the contact resistance. I keep a small burnishing tool next to me on the bench for those jacks.

[Valvehead]

The contact resistance on all 3 contacts is 0.1 ohm . I tried inserting a stereo plug into this jack and shorting the other end in each possible way. This didnt work either.

[Enzo]

Send me an email with Crate GLX65 schematic as the subject line. Send it to:

tmenzo at msn dot com

[Valvehead]

i wish i could find the schematic online.

I may have to buy one from Crate.

I dont see any relays on that end of the board, are they using some other method to switch i wonder? I dont hear any relays when going from the Rhythm channel to the clean channel. The lights change, but no "click" .

[Enzo]

I said:

Send me an email with Crate GLX65 schematic as the subject line. Send it to:

tmenzo at msn dot com

I'll send it to you.
If that isn't online enough for you, I am sorry.

[Valvehead]

Thats the scem--but i dont see how they are switching between the 3 channels . Q1 or Q2 ?

[Enzo]

Q1,2,3,4,7,21,25,28,29 Couple others switch DSP.

COntrol voltage B runs Q1,2,28
COntrol B1 runs Q7
Control C runs Q3,25,29
Control A runs Q4,21

And I might have missed some.

[Valvehead]

thats way over my head enzo...........



any suggestions on what to look at regarding the non-switching?

i dont even see a switch symbol on the scem---while there are 2 actual pushbutton switches on the front of the amp .

[Enzo]

I sent three sets of drawings. One was just a jack or something, one was 18 pages of the DSP, and the other was the two page amp curcuit, drawing 561.

On that drawing, page 2, far left, lower left corner, that is the switching circuitry. At the left edge is a 6 pin connection J21. It is the wires that go over to the actual FS jacks on the chasis. When nothing is plugged into the FS jacks, the internal cutout contacts of the jack short pins 1 to 2, and pins 3 to 4. Pin 5 is ground and the other stuff is DSP which is a separate iszue.

Immediately to the right of J21 are the two panel switches - SW1, SW2.

Sw1, when closed, grounds pin 2, whuch is connected through the jack to pin 1. Pin 1, follow the lines down to the diode D25, then shirts the top of D25 to ground or not, depending upon the switch. D25 is a zener. It makes 3 volts across itself, powered by the 16 volts coming through R74 above it.

That 3 volts will turn on Q22 there. Grounding D25 removes the 3 volts and Q22 turns off. The top of Q22 goes to a little box called B1, and also a couple more B boxes after some resistors. When Q22 is on, those Bs go to zero volts, and when Q22 is off, they rise to 16v or some other positive voltage.

That list of transistors I made? That B voltage goes to all those transistors, turning THEM off and on. While we are at it, the B voltage turning off and on also works Q30, whose only job is to light the SOLO light.

SW2 controls Q17, whuch turns the A voltage off and on. A goes to all the transistors I listed for A.

Now go back to page 1, where the preamp circuits are. Right in the middle are the SOLO and RHYTHM level controls, P6, P12. And below that the clean volume control. The wiper of each of those feeds to a transistor - Q28,25,21, in this example. Those three transistors all gather together to feed their signal throuh C49 and into IC4B. Each transistor is controlled by the little box with a B or an A in it, the same B and A voltages we just discussed.

Those transistors are JFETs - junction field effect transistors. JFETS act like a switch. Their S and D terminals are connected together inside unless the third leg - G for gate - turns it off. So in teh case I just described with the volume controls, each transistor is turned off or on to select which volume control to pay attention to. WHichever one os on at any time passes the signal from its associated volume control on to the rest of the amp - they select which channel we hear.

ANd there it is, channel switching.

You can hook a bunch of JFETs to one control voltage, and they can be scattered all over. You switch to the clean channel, and one selects its volume contol, at the same time another alters teh gain of another stage.

[Valvehead]

thanks--i will try and start testing in a couple days

[Valvehead]

I found the following today:

Bear with me Enzo...

R74 does have 16v across it, regardless of switching.


D25 does NOT have 3 volts across it, but one end does ground good. It only has 4mv across it.


The junction of Q22 and C48 stays at 12.3v regardless of switching. Shouldnt that go from 0v to 12v ?


I notice that when pushing SW 1A in/out , that one pin stays grounded .

when pushing sw 2A , the ground lifts on sw 2A.

[Enzo]

R74 has 16v across it all the time becasue something is holding down the top of the zener. C48 junctions with Q22 at both ends. Please use terms like emitter, base, and collector. If you are unsure, the emitter is on the bottom here, it goes to ground directly in the case of Q22, and is always the one with the arrow. The collector is the one at the top, at the other end from the emitter. Here it goes to R67. The third terminal is the base - on the left side of Q22. The base of Q22 connects through R81 to D25.

SO if you mean the collector of Q22 ought to go up and down, you are right, but it can't if the transistor is not turned off and on at its base.

ONly so many possibilities here: D25 is shorted or very leaky. the switch is or the jack is shorted or has a solder bridge to ground. Or Q22 is bad.

WHat resistance is across D25 with powr removed? It is a diode, so it ought to test like one. If low, then we need to find out why. Any of the three things above could cause that. So unplug the ribbon to the jack. Any difference? Would eliminate the jack assembly.

When Q22 is on, there will be about a half to a full volt at the base. But when it is on, the collector voltage will go low. Yours is not.

The zener is there to protect the Q22 from excess base current and transients from the jack. I don't know that the voltage there ever gets all the way to 3, but it goes up to something when the switch is open.

Issolate the problem to the jacks, the switch, or the electronics. Unplug the jacks. Does the zener come up? You can use a grounded clip lead to ground that point or not to exercise the circuit.

[Valvehead]

Enzo--you are the man!

it was D25 , tested bad . I had another diode (same one) sitting around so i replaced it.

switches channels great now !

THANKS