CRATE FXT 120/Reparied Then worked 2 weeks then failed Again Same symptoms???

[hughz]

Hello,,, Glad to of found this site as it helped a lot so any more input to help trouble shoot as to why this amp has went mute again is greatly needed and appreciated!!! Thanks in Advance!!

I have a CRATE FXT 120 That had No sound issues then I replaced the fets and it worked for about 2 weeks.. I did no prior test to see if I could get it to work the first time while no sound was present I just decided to replace the fets and it came to life again!!

After it failed to produce sound a second time after working for 2 weeks I jumped a patch cord from the speaker input jack to the rear DSP input by only inserting the tip of the 1/4 plug into the jack as all the way inserted gave me almost no response and horrible noise.. But touching only one tab on the rear of the DSP or the Channel gain select input it came back to life!!

Here's the quick breakdown to clarify--------Guitar is plugged into the input on the front by the on/off switch-------at the other side of the amp front by the knobs next to the reverb chorus effects onboard there's a insert jack and a speaker jack with a speaker symbol next to it.. The Back of the amp has only 2 input jacks----channel Gain Select---and DSP input for the onboard FX to run for your guitar sound overdrive channel...

I don't use the DSP I run on the clean channel and an off board processor for my preference.. Upon jumping the speaker input to the DSP jack on the back both channels of the amp work but you can only insert the 1/4 inch plug to the first tab on the DSP jack or channel gain select input and it will jam like it did before..

So I did check all my work and solder.. I inspected any other bad solder joints that may have occurred over time.. Jacks look clean or new.. Also the amp has been well kept and looks new---its just been played.. The speakers still sound great..

Also I have never been in need to run this amp at full volume or even half way with an off board processor.. After replacing TIP 142 and TIP 147 Fets it worked great and was only on volume 3 before it went silent..

One other thing the insert jack on front does not do anything in any combo to jumping it with a patch cord----only the speaker input can be used in combo with jumping a patch to the rear jacks only plugging into the first tab of the jack on back of amp..

Any ideas to trouble shoot would be excellent!!!

[52 Bill]

I will assume that English is not your primary language, because some of the terms that you are using are confusing to me.

Your guitar should be plugged into the jack marked input that is located on the front panel next to the gain 1 control. It is on the left side as you face the front of the amp.

The two jacks that are on the right side of the front panel are the insert jack and the extension speaker jack. The insert jack is like an FX loop, but it is a single stereo jack and not separate send and return jacks. The extension speaker jack is there to add an additional speaker cabinet to the amp.

Both of these jacks have switches built into them that interrupt the signal path and can cause the amp to stop making sound. They should both be sprayed with a little DeoxIt type cleaner and a plug inserted and removed from the jack a few times to try and clean the switch contacts.

The rear panel has two jacks on it that are for foot switches. One to change channels on the amp and the other to turn on and off the DSP FX.

Do not plug a cord into any two jacks on this amp. It can cause damage to the amp.

[hughz]

Previous post is a little long but it was how I went about trouble shooting my Crate after replacing the parts and then it not working again..

Hopefully this is better termed and simplified----- I always get contacts are dirty use Cleaner DeoxIT,, change cords,,, check fuse,,,told what an amp is basic training blah blah blah..

TIP 142 TIP 147 replaced---Contacts clean internally cleaned 1/4 inch plugged it to death----POTS Clean

Worked great after replacing FETS as it had no sound first time it broke down-----OR not producing sound--Dry Solder joints????? inspected tested looked over double check the obvious loose connections

Terms are as follows that are listed on the amp------- Input by gain 1---or overdrive side---insert jack and speaker jack front side with POTs---potentiometers-----Back side jacks/inputs are DSP jack and channel/gain select-----1/4 inputs... all cleaned still no response------mosfets---transitors--FETS--Black Nickel size squares--- Tested and seem fine still...???

Jumped it with a patch cord---yes maybe a bad idea but sound produced when doing this when applying the plug or cord to 1 tab contact on the back side 1/4 inch DSP jack--Or the channel gain select tab--any tab on the jack input brought the signal and produced sound--

--I had the board out to touch the tab on top of the jack exposed... Other end was plugged all the way into speaker extension input--on front side.. Sound came out of speakers nicely..????

Any Seasoned Pros electronics techy peoples out there that could give some much needed knowledge would be very well appreciated----

[TomCarlos]

Just an fyi.... the TIP 142 and TIP 147 are not FET devices (Field Effect Transistor). They are Darlington Pair Transistors.

Datasheet

Check the datasheet and test to make sure them appropriately. Chances are these would not fail on their own. Something must have caused a problem (if in fact the transistors are blown once again).


Tom

[g1]

It sounds like there is a problem with the ext.speaker jack. It is either defective or has a bad solder connection or cracked trace/pad.
When you are connecting that extra cable and you get sound, you are completing the circuit from the speaker's neg. terminal to ground (normally the ext.speaker jack should do this when nothing is plugged into it).
To verify this, locate JOW2 and JOW4 wire jumpers on the circuit board. Connect the 2 of them together with a piece of wire. Do you get sound now?

[hughz]

Gonna jump those 2 together and see right know... I'll post in a moment on the result...JOW2 JOW4..

[hughz]

g1 YOU ROCK MAN!!!! Never was a FETs issue!! Go figure.. The Darn Extension speaker input has 2 pins.. I checked them before however The back Pin upon Re-inspecting it was just BARELY lifted from connecting to the rear contact..

I could not tell at first and really wasn't sure if it was lifted still until I messed with it and went ahead and bent the under side up to make it connect to the top tab..

Plugged it in like you should to input and Boom Sound..

Still weird after replacing Transitors Darlington pairs that it worked for a short time.. Must be the weather causing expanding etc. As heat builds inside the amp... I would guess...

The amp sat for months in the summer when the issue occurred and I swapped TIP 142-147 in the near winter so that I'm sure played a part to the tab contracting during that time as it was colder..

Good point The simplest things such as this I will keep in mind next time.. Check input tabs are connected all the way.. Duh..!!

Thanks for the help!!!!!! Awesome!!!