• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Problem with GK 700RB I combo fan

S

Stakes_Is_High

Apr 14, 2012
19
0
#1
Hey guys I have a GK 700RB I combo amp and I well aware that there is a thermal range in which the fan begins to spin. After extended playing, the amp is not hot to the touch but is noticeably warm and I have never seen the fan start on its own. If I blow into the fan grating from the top to rotate the fan it will remain spinning. Anyone have any ideas on how I can make sure the amp is receiving adequate cooling?
 
#3
You probably didn't get a response because (maybe) no one who read your post has that exact amp.

Maybe someone with a standalone 700RB head will reply. Your amp's fan should come on at least as early as the fan in a standalone 700RB head, since the combo head is running in a closed box (rather than in free air, with the minor benefits of convection), and so appears to rely exclusively on air pulled in through the top vent for cooling.

How hard have you been running the amp? At anything over bedroom practice volume, like at a practice or a gig, imo the fan ought to be spinning, unless it's winter where you are and the areas you're using the amp in are cold. But you can always call GK tech support and ask. Whatever they tell you would be the definitive answer.
 
#4
Thanks for the response. I've been pushing it near 12 o'clock on the woofer volume and at 12 on the preamp stage for about 1-2 hours at a time and it's quite hot here. The amp is definitely warm enough to warrant at least some fan rotation. I'm just wondering if it's a circuit issue because if I blow on the fan to make it rotate it uses the momentum and then begins to work. Unless I provide the initiation of the fan rotation it does not seem to start on its own...
 
#5
Stakes_Is_High said:
Hey guys I have a GK 700RB I combo amp and I well aware that there is a thermal range in which the fan begins to spin. After extended playing, the amp is not hot to the touch but is noticeably warm and I have never seen the fan start on its own. If I blow into the fan grating from the top to rotate the fan it will remain spinning. Anyone have any ideas on how I can make sure the amp is receiving adequate cooling?
Click to expand...
If you blow into the fan it keeps spinning that sounds like the fan has some dust or dirt that keeping it from spinning.Ive used contact cleaner with a small compressor to clean them & never had problems.Fans get very dirty & need to be cleaned every so often.Some amps have a filter even to help stop the crap from getting into the fan & the amp.
FTR- My first Powramp has 2 daul speed fans & only one was working right out of the box.The tech said that fans are the most common problem with poweramps heating up or bassamps for that matter.
 
#7
@Growly that's a good point. I didn't mention before but after it starts spinning it isn't really a smooth fan sound either it is a little squeaky and clicky sounding. I'll try to open it up and give the fan a good cleaning. If that doesn't work I think I'll give the GK service number a call.
@4strings that's exactly why this fan issue is worrying me. Thankfully this amp tends to run relatively cool but I don't want to rely on pure luck for this thing not to burn out.
 
#8
I have had that combo, which is just a 700rb stuffed into a wider rack. I have also owned a 1001rb, 1001rb2, and a 400rbIII. The fans on all of them do not come on until after some playing, and it usually has to be up for a couple minutes to get the heat for it to even start moving. My 400RBIII had a faulty fan circuit that kept if from turning on at all, and I didn't realize that the amp had a problem when I bought it used until it shut off on my frist practice about 4 songs in. I never hear the fans in the GK amps run.

I ended up pulling the cover off all the amps and pointing a hair dryer (on it's hot setting) right at the temp sensor for the fan circuit. After a couple minutes, the fan started turning on. Be careful because of the exposed electronics.

Wes
 
#9
@Wes I haven't opened it up yet because I have to get some deoxit and compressed air but since you have had the combo amp before, is the thermal sensor in a fairly obvious location? I'm not exactly sure what it looks like as I've only opened up this amp to check a fuse.
 
#10
Take a look and see if you can find it. I believe you will find some wires that come off the fan back to a circuit board, then off the board to the temp sensor. If you can't find it, I'll pull an amp out of the rack and take a picture for you.
Wes
 
#15
Thanks again for responses guys. I just bought some compressed air and took out the power amp from the cabinet housing. Is the thermal sensor just a part of the heatsink like a CPU? If that's the case then I'll just try the hair dryer test on the heatsink after I clean the fan. I might even try the fan in one of my computer builds to test the fan alone.

@Novax I think there is a protection circuit but the test apparently passes because the start up light is red for a few seconds after turning on and then turns green which is what is supposed to happen from my knowledge at least.
 
#19
Alright guys I just performed the hairdryer test and noticed two things. I watched the fan closely during the entire process and the fan "twitched" after a few minutes of heat on its own but did not spin. I flicked the fan and it immediately starting spinning. Second thing I noticed was that after the fan remained spinning, I paid attention to the sound of the RPMs. I continued to use the hairdryer for a few more minutes, and the sound of the RPMs indicated that it did in fact speed up.

The conclusion I have reached is that the fan is no good but the thermal sensor is still functioning which means it's an easy fix. I'll purchase a replacement fan and report on its function once I install it.

Thanks for the suggestions! Much appreciated. Now I just have to figure out if I can get the horn working as the horn amp does not appear to have any response at all as I tried to post about a few months ago here if anyone has starting point. http://www.talkbass.com/forum/f15/tweeter-issue-gk-700rb-model-1-115-combo-873436/.
 

Latest posts

Top Bottom
Back