No volume with Crate GLX1200H

[DJ_Critterus]

Hi guys. First time poster, long time reader here.

I bought this GLX1200H/cab in working condition as a spare practice amp/cab. About a month later, I ended up with very low volume with the master and everything else cranked to 11 . I am also sure that the mute button is not engaged as it will get a little bit louder, then a loud quiter when I change settings with it. I've had it hooked to several different cabinets with the same issue.

With some of my better guitars I get a loud hum. I also don't have the foot pedal yet and it will be in Tuesday. Could there be something wrong with this circuit causing this issue?

I tried calling Crate and the only answer I received was that it could be a bad power supply, I'd have to fill out a waiver for a schematic, and I never received it.

Any help would be greatly appreciated and let me know if you need more info to get better insight.

thanks,

DJ

[DrGonz78]

What happens to the volume when you ball up your fist and give it the ole' Enzo love tap??? Does banging on the amp suggest any loose connections or intermittent behavior in the volume. The title suggests that there is "No Volume" and the post description say's "very low volume", so which one is it or is it both? Either way we need to test the preamp and try to isolate the power amp. Does the amp have line out or effects out(send) jacks? Plug that into another amp to see if the symptoms are the same or if the preamp is working properly. Even connecting a cable from the send effects to the return effects jacks can help trouble shoot the amp. The main thing we want to know is if any of the contacts on these jacks is dirty and causing interruption in the signal path. Also, need to isolate the problem more. Give as much detail and ask as many questions, Good Luck.

People that just say "it could be a bad power supply" are not really giving great advice. The loud hum can be a number of things on the signal path and even on the power supply side(Main Filter Caps).

If you call Loud(Crate) again they usually are pretty good about getting the schematic sent by email. All you have to do is respond to their release waiver email and they send it over really quick.

[DJ_Critterus]

Oops. I posted that wrong. It's extremely low volume. I have tried plugging into the effects circuits per the troubleshooting from crate and it's the same issue. The good ole love tap didn't do anything except make a loud thump and get me wondering if a BFH would work better

It does have the send and return effects and I don't have a cable connecting both of those if that is what you are also referring to. I'll have to get my other amp out of the Jam Trailer tonight so I can try the other test you mentioned (we're not a garage band...We're a trailer band )

I think I found the correct schematic online and will look at that after I get better warm and fuzzy on what's going on.

thanks for the help and hopefully I gave some better info this time.

DJ

[SpareRibs]

Hello,
I have a Crate GX-40C I bought used with a similar problem. The send and return jacks are the problem. You will
have to clean or replace all of them as they are part of the circuit. It really sounded strange to me, but it worked. Check it out on the schematic.

[DJ_Critterus]

Thank you, SpareRibs. I'll work on that tonight and see how it goes. i do have a question. If the send and return jacks aren't being used (effects send/return i presume) how do they effect the circuit?

[g1]

There are usually switches in the return (and sometimes also send) jacks that close when nothing is plugged in to them. The signal routes through those closed switches. If the switches get dirty/oxidized, the signal may crackle or fade or cut in and out.
This explains switching jacks: http://music-electronics-forum.com/a...ck-problem.pdf

[Enzo]

So if you are NOT using the FX loop jacks, plug a spare cord from send to return and see if it wakes up the amp. VERY common problem on any amp with FX loop jacks.

[DJ_Critterus]

Thanks guys. I have been in and out of the hospital for a few days and am finally home. I'll try what Enzo suggested first before I go tearing things apart to clean them. Updates coming in a couple of hours.

[DJ_Critterus]

O.K. Here's what's happening. I plugged a cable into the effects send and return. I still have the same problem. What I am noticing now, since I never used the switch to turn on the back lights for the control panel, is that it flickers depending on how hard or soft I play. I will try cleaning those jacks later (need to get some electronics cleaner) when I am back to feeling well enough to drive again.

Could this actually be a power supply going on the frits?

[Jazz P Bass]

Could this actually be a power supply going on the frits?

You will never know unless you monitor it.

[DrGonz78]

Yes monitor the voltage as Jazz says... You found the schematic right? Post it... I only could find the GX1200H model but maybe they are very similar on the power supply side.

One gut feeling I have... There is typically a ribbon or braid cable that connects the preamp circuit from the power board. I would have a look at the voltages there too as we are *assuming* this is a main power board supply issue. We really have not evening gotten that far. Thus check voltages for the power amp and preamp circuits. We need to make sure the power board is passing the preamp voltages correctly. Let's see what we are looking at in numbers.

[Enzo]

Here:

There is also a sheet for teh FX card, and another sheet for just the FS jacks. I don;t think we need them, but ask if we do.

[DJ_Critterus]

It looks liek the transformer is bad. I am getting power on the board where it connects, but I am reading nothing when I test the primary leads to the transformer. The leads ont he secondary side are showing good, so it definitely has to be the issue. Now, I need to find one somewhere.

I am having trouble locating this part, but will probably have to call CRATE int he morning. It looks like the part# is HK76H-137 and another set of numbers on it is TT0760208410-E. Does anybody know of a site where I can use these part numbers to find the exact transformer or a suitable replacement?

[Jazz P Bass]

If the transformer is bad, how can the amplifier function at all.
There are test points on the schematic that Enzo posted.
The Primary is where the AC wall voltage enters the transformer.
The Secondary is the 'transformed' voltage.
After the rectifiers you should read + & - 40 volts dc.
TP 14 & TP 15.

[DrGonz78]

I am getting power on the board where it connects, but I am reading nothing when I test the primary leads to the transformer. The leads ont he secondary side are showing good, so it definitely has to be the issue.

Remember to express your findings in numbers and not generalities, be specific please. Show us in the underlined parts of the your statements here the voltages you tested. The power transformer is not something you want to rush out and try to find/replace. Chances are that it is working and we are not measuring something correctly. How are you measuring?