Problem with function Generator - Page 1
Forum section: electronics / beginners

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 06, 2012, 03:52:51 pm
content: My function generator has developed a problem as seen in attached pictures it uses a 2206cp chip in a chip holder ,so i'm wondering if this is going bad,i've had a look around nothing seems to be burning or popped, I wonder if they put it on a chipholdersocket because they will go wrong, any way ordered one cost £2.00p free postage, has any of you seen this type of fault before, it also crossed my mind if it was a capacitor starting to go down this happens after approx 10 mins it's fine then it jitters a bit into full distortion.Paul

author: SeanB
author_rank: Super Contributor
timestamp: October 06, 2012, 05:38:25 pm
content: Probably a bad chip. If it runs hot it would be a good idea to freeze it when it is faulty and see if it comes right. If so put a heatsink on the new one to keep it going for longer.

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 06, 2012, 05:43:06 pm
content: Thank you I've got some small heatsinks would a dot of epoxy be ok

author: SeanB
author_rank: Super Contributor
timestamp: October 06, 2012, 05:53:37 pm
content: 2 part epoxy does work well, you can get a thermal epoxy as well.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 06, 2012, 06:11:06 pm
content: since you provided very little info, only a signal picture with no scale whatsoever and a chip which i cant find the datasheet, so let me give my shoot which i prefer most. your chip produces ringing due to bad pcb or connection. using socket introduces significant inductance coupled with stray or bypass capacitance and the right temperature will force the chip into oscillation...is the chip recovered after turned off and is the fault repetitive?

author: SeanB
author_rank: Super Contributor
timestamp: October 06, 2012, 06:15:33 pm
content: XR2206, a quite old design, and reasonable in it's day.

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 06, 2012, 06:47:41 pm
content: here's the latestif I turn the F/G upside down the chip is the right way up it works fine, but then if I turn the F/G the right way up, so the chip is upside down the fault appears. so I'm going to take the chip out, carefully cleanpins and see what happens Hmm.

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 06, 2012, 07:02:37 pm
content: No difference , I have noticed that I have the sine wave up which has gone large as it's been doing, if I zoom in it's made up of small sine waves 6 layers and zoomed out it's one divison wide ,same on triangle & Square.

author: saturation
author_rank: Super Contributor
timestamp: October 06, 2012, 07:11:56 pm
content: I'm not sure what type of quality this device make is, but If changing positions did something, that can help quite a bit; look at the solder joints. You can also operate the device with the lid off, due care of course, and press on the IC and other components to see if it makes a difference, either if it repeats the problem or fixes it.

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 06, 2012, 07:18:17 pm
content: OK this is how it looks at the minute scope setting remain the same .5 volt/div, 200 us time/div as its always been function generator square wave 100k, coarse @8 fine @0 dc offset 0 /amplitude /0.25%.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 06, 2012, 07:36:27 pm
content: Like what was already said before, if turning it upside down changes the waveform it must be a mechanical problem, examine the PCB and the connections to it, and also any earth connections. Looking at the first picture you posted makes me think that it could also be a power supply problem, like when there is a lot of AC on the supply, maybe the output capacitor is loose?

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 06, 2012, 07:44:41 pm
content: I think I've found it one of the small electrolyic capacitors up near the power supply, the screen was as the photo I wiggled the top of the capacitor,the wave shape came back to where it belongs, so think I'm going to change all 4 of the caps in that area and see where it goes looking on the inside it was manufactured in 1984, so perhaps they will start to play up.This could be my first serious repair, it's quite exciting.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 06, 2012, 07:51:48 pm
content: Or it is just a bad connection... good luck anyway!

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 06, 2012, 09:49:59 pm
content: Hi Everyone, update on my function Generator the caps I changed were 10UF 50v, I replaced them with Sanyo 10UF 100v, put it altogether and it's worked fine for the last 40 minutes, so fingers crossed, I have out of curosity kept them for when I get a ESR meter and see exactly whats going on, just incase it was dry joints, thank you for all the advice. Here's a picture taken seconds ago ,must have been on for 1 hour by now.Paul