Thanks, guys !
I'm not shure enough in my abylities to fix this, so I'm gonna take it to qualified person.
Just sad that it's worked that way...

Arghhhhhhh ! So it looks like it's out of my hands. I have to take it to repair, damn.
Anyway, thank you Phil and Roly !

Great tips for cleaning, guys !
But, here we go again !
Yasterday I took the amp to my friends house for jamming and rehearsal. He's living a 100 m from me and I've transported the amp with a two wheel troley (or whatever you called it)...no too much bumps or anything...
And when I power up the amp, first there is no sound at all, completely sound dead. I thought that there some guitar cable has problem but when I changed it nothing has happened. Then, all of a sudden, it comes back. BUT...
I've played 20-30 seconds and previous sindrom comes back : farting or no sound at all. I have briged loop with guitar cable expecting a solution but nothing's happen. Then I realized that, when I slightly pulling out the main input jack from socket something crackle and the amp come alive. After that, I've put some contact spray on jack of the cable and put in-pull out input socket 20-30 times. And the amp start working...for maybe a minute than stops again. Than I went REALY pissed of and plug in another amp to finish the rehearsal.
Now, i found ineresting the fact that I have tried to rock input socket while the jack were still in it back and forth, left right and up and down and nothing cracled, nothing happened at all. I thought that it will crack or anything if the socket maybe have faulty soldier contact, but nothing.
In the end my fellow bass player said that I should try to power amp once again (despite all, they really liked how the amp sounds when it's working)) and I did and it works about a minute and then died again.
Now I'm really furious because I know a previous owner and believe him when he said that the amp worked with no issues, but now I don't know what to do. I know to fix guitars but don't how to fix an amps and don't have qualified repairman for the task ( from aforementioned reason). To complete irony, I had offers to sell the amp before this happened and, of course, they are withdrowned. Damn !

Thank you, guys for your help !
Amp now works with no problems !
When I briged send and return loop inputs with cable, problem egzisted only to the point I have removed jack from send input and then amp come alive. From then, I plugged in and unplugged jacks to both inputs several times and amp works as it should.
That hole in the ground is scary, however, your idea is still tempting...
I realy like this : "An amp is an amp is an amp..."  :tu:
This is my point of view regards guitars : I like to tune them in every possible way, just to make them best they can be, cheap or expensive. All of them are instruments that can make happy someone trying to make music ! :dbtu:
So, once more, thank you !

Thnx, Roly !
Tried to connect and disconnect jacks of the loop several times while amp still working and, from then, everything still works !
I even powered off the amp and just before few minutes powered it on and plugged guitar and -IT'S STILL ALIVE !
I hope that it'll remain that way. Maybe nothing is broken after all !
We'll see. If the problem persists or return I'll be back !
Thank you for everything once more !

Thanks for your input, guys !
Anyway, just power up the amp and , of ourse, farts. Again, I tried to rock speaker wires and so on and nothing happened. Than used one cable to connect loop and problem remains. BUT !
When I was disconnecting loop cable, when I pull out send jack than , amp come in alive ?
And, now still is. Can it be the problem ?
BTW, I tried to seek help from our amp gurues but fixing a solid state is...mmm...I don't know your phrase...but they think that SS amps are garbage and not worth their time

Hi everyone !
I have found a simmilar topic but not replays for a long time so I decided to start a new one.
Yesterday I have recieved used Hiwat Maxwatt G100R and when I plug the guitar signal was waaaaay too weak and amp is producing a kinda farting sound. I have mess a little bit with controls, switches and everything and channels were switching, gains were switching (for tone controls is a little hard to say from obvious reasons)...I checked cable, input, guitar (replace guitar and cable) and nothing changed. Then, all of a sudden it came alive and everything seems to function perfectly. Then I played guitar for a while (15-20 min) and - BAM- how it came, it goes same way, started to fart and cut output signal to 5% (not dead completely). Then I try to hit it from up above (Russian principle  :tu:) and then it start to come and go, than it went for good. I had to go somewhere but when I come back after few hours I plugged it in again and-it worked perfectly. Than I become pissed off and, while guitar was plugged in and on the drive channel, with one hand plucking the guitar and with another hand I grabbed it for handle and rock it back and forth for some time, trying to provoke upper mentioned situation. And after 10-15 rocks it went off the same way.
Afetr that, I have try to rock and pull wires from speaker but nothing have happened. I have plug out the guitar and amp from outlet and roll amp on the front side and look at speaker again, checked wires but everyrhing seemd to be ok.
Today, I contacted previous owner but he swears that the amp was in perfect order.
Is it possible that something gone wrong in transport ?
Please, if there is anybody that experienced the same with this amp, or somebody that think that he knows what's going on, give me replay !
Thanks in advance !