Cheap XR2206 Function Generator Overheating...

Question

Hello All,

I've been working to learn more about analog circuitry, for this purpose I decided I would try a XR2206 bases function generator cheap yes, but hopefully a place to start. When I first received the unit I tested it (can't give a positive rating on eBay unless it works) and I was able to see the three waveforms. They had soem jitter and other issues but overall it worked.

Today I decided to get start really working with it and noticed that the XR2206 IC started to get very warm. As I was not 100% I had connected it the right way, I tried connecting it in reverse (probably not the smartest idea thinking back). The IC was still getting pretty warm and this was not even with the voltage at the recommended level (using 5V instead of 9V, I always start from zero and turn up the supply). I then disconnected the GND from the oscilloscope and the IC started to cool off, connecting it again and it heats up. I have now tried this with two scopes (TBS 120B-EDU and DS)X1120G) and the same thing happens with both of them. I do know that the plug all my equipment is connected to is not grounded (old wiring, looking to rectify this just not sure how at the moment).

If anyone has some ideas as to why connecting the scope would cause the IC to heat up I would be very interested in then and exploring this issue further.

Thanks

Kas

P.s I'm not sure that this is the right group to post this in but, I'm not sure where else this should go.

ewinter2112 · Answer

I purchased one of these as a project for my grandson because it was inexpensive. And you get what you pay for but still well worth the money.

I cant speak to you specific issue but .................

To begin with there are a few design errors that will cause minor pain but nothing major such as R1 s/b 10k. R2 is wired backwards (clockwise decreases amplitude).

R7 and R* s/b 10:1.

Amplitude pot is linear taper and should be logarithmic,

And other omissions in the design and incorrect values.

But what was found was that the XR2206 ic included in the kit is not an authentic Exar part. (logo marked on part and it has fake datecode.

It does not operate over the VCC specified range with stable output freq. and other issues.

if you purchase an authentic part you will see a big difference.

Here is a long boring video that describes some problems with the design.

https://www.youtube.com/watch?v=02XtneCHnDA

Keep in mind, all indications are the Exar (now maxlinear) XR2206 is obsolete.

michaelkellett · Answer

If it's drawing 220mA then the chip will get hot (3W at 14V makes for a very hot chip) . Almost certainly the chip is blown. It's a very long time since I used one of these and I can't remember how easy they were to blow up. I realise that you want to learn about analogue circuits - do you want to make a signal generator or was playing with it a end in itself. If you want a signal generator I can make some other suggestions that are not based on obsolete parts and might be more forgiving. MK

kas.lewis · Answer

the-dubster , From what I can see it's consuming 0.22A with a supply of 14V. After disconnecting the scope it's still drawing the same current. Maybe it was an illusion that it was only over heating when connected to the scope. (Its also fun doubting yourself after the fact ). Kas

kas.lewis · Answer

Hello michaelkellett , I don't have a good picture of the schematic but I have included one that I have. I should mention as previously mentioned it appears the scope is not having an effect, I just thought it was at the beginning. Doing a second test has shown the IC heating up even with no scope connected. This is the setup, cart is there just to ensure the two power points don't touch each other. Here is the schematic, sorry for the really bad quality. Thanks Kas

kas.lewis · Answer

the-dubster , I hear you, once you get to the exciting part it's all downhill from there. However in this case I think the exciting part is the end goal seeing if I can see what is broken. Fixing it I don't think is possible (the silicone is probably gone) but I've often wondered what happens when an IC is blown. If the SlowMoGuys or SmarterEveryDay could video in super slow motion the inside of an IC as it blows that would be pretty cool and interesting... I think. Kas

the-dubster · Answer

jw0752 apparently the scope and PSU are not currently grounded - the plug they connect to does not have a ground (old wiring according to kas.lewis 220mA is WAAAAAYYYYY too high @ 14V! (Absolute maximum rating IIRC is 750mW - 26V @ 20mA is only 520mW - You're ripping 3W plus through that! Does it still produce the waveforms out? I suspect you may have a goosed IC . . . .

the-dubster · Answer

I'll be completely honest kas.lewis the pun was purely unintentional! I spotted where it was after you said!! I can see why that would be interesting, plus it's quite often as far as I get when trying to fix things! "ooohhhh, it's open, I'll just see if I can . . . . . . right, bored now - I'll put that aside and look at something else". I have loads of things at that stage.

Cheap XR2206 Function Generator Overheating...

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