openrcforums

jhsa wrote: Hmm, would placing a resistor in series with the trims switches, or increase the value of the existing ones fix the problem?

João

It is easier to add a resistor into the switch wire, than it is to change the smd resistor. At least for most people. With the resistor in the switch line it does change/discharge the capacitor more slowly.
-Gohst

jhsa wrote:Any chance of someone having this problem trying to bypass the 5V regulator and use another one with more power?

7805 fitted bypassing 100mA 78L05. No change.

you're fast

NOT replacing the existing resistors, they are AFTER the de-bounce capacitor.
Adding a resistor in the wire from the trim switches will drastically reduce any spike caused when switching. Not having a resistor is, in my opinion, poor design.
Flaps: Since you have a Tx with the problem, perhaps you are in a good position to try this fix. A 1K resistor should be fine, the capacitor will discharge inside 1mS, but the current will be limited to 5mA. The 1K will also provide a low enough input voltage to the processor to guarantee a logic 0.

If this does fix the problem, then it sounds like it should be done to all 8 trim switches, the 4 direction buttons and the MENU and EXIT buttons.

Maybe I can find what the effect is that causes the reset, e.g. is it the regulator, a processor brownout, the processor seeing a reset pulse, or what.

A thought, are the spikes, that are likely a negative spike on the ground signal being coupled into the processor reset by the large tantalum capacitor on the reset signal. Port D, the trim switches connections, is close to the RESET pin. May be a first test is to remove the RESET capacitor and see if that solves the problem.

I'll see if I can get my '128 board in a Tx for testing.

Mike.

Reset capacitor removed. No effect on the fault.

Will try the resistor fix now.

Flaps, (...so...) you (...do...) rock!

yes, but don't tell her. sshhhhh

I have never been called a rock.. Ohh well. First time for anything.

Okay. RHS horizontal trim was redone, as a ground path was found to still be intact. One 820 Ohm resistor fitted in series with each trim switch. So far it seems to have sorted out the problem. Still to do the other side.

In this case is it the same inserting the resistor on the ground side of the switch circuit and on the other side? If that is true, then a weak regulator and the voltage spikes are eliminated

I've just taken the board you modified out and inspected it (Reference to edited post, picture no longer in the post). What I think you have in fact done is to cut a track that is joining ground to the sticks and added the 820 Ohm resistor across that. There is a ground plane on the other side of the board.
It looks to me that the vertical trims are wired directly to the 9-way connector on the main board while the horizontal trims have the sticks wired through their adapter board.
Counting from the right in your picture, I think the connections are trim, trim, ground, stick, stick, analog power. The horizontal trims are connected to ANALOG ground, the vertical trims are NOT.

Mike.

Edit: Analogue ground is connected to digital ground via a 10uH inductor on the main board.

Yes I revised what I did earlier. Which was edited out as soon as I realised that there was another ground path on the other side of the trim board. So now there is two resistors. One connected to each of the trim switches. Track is cut where the red lines are.

Both sides are now modified. No matter how much I click the switches the system will not reboot.

The unmodified transmitter acts the same way without the modifications being done. That one is a later one. I wonder if they changed anything because they may have found this problem? Mind you. I was using the 'faulty' transmitter for a long while with the m64 without anything showing up..

I have to admit that I feel a lot better having replaced the 100mA 5 Volt regulator with a 1 Amp one.

That sounds beautiful! can you please post pictures of what you have done exactly? I'm not shure if I get it right what is to do. As soon as I get my new M128 I will try it (and see if the board is still alive

Chris

Thanks for the pic, I was too slow on my mobile...

I understand now why it is only the horizontal trims causing the problem. It is poor design to use the analogue ground for a digital signal.
The 'best' solution would be to provide a proper digital ground to the switches, but the resistors are easier to do, and seem to sort the problem.

Can you confirm whether you have M128s or M128As on you boards, just to have some completeness as to what is causing the problem to which processors.

Mike.

If only this issue was found BEFORE I decided to resolder my m2561 & apparently damage my main board. Strange that one of my two m128 transmitters had this issue, solved by replacing the m128. Both have been working perfectly for months...

I've had a M128 with the trim problems. Next I will probably try a M128A, depends on what will arrive first.

Chris

I have a 128A and no issues.

I wonder which chips I have on both my radios, because I have no issues. At least never found any..

Bought my chips from Ebay from a seller (sharpseller2000) who was selling them in pairs. Both of mine are 128 - 16AU .. One TX fine other had to be modified.

Same to me, same seller, same chips.
One tx modded, no problems (up to now)

Reinhard

hhmmmm I think i bought from the same seller.

http://www.ebay.de/itm/330583868266?ssP ... 1423.l2649

On the product page scroll down and see what it says

This auction is fo 2piece .........(A54)
ATMEGA128-16AU MCU Memory
ATMEGA128A-AU Genuine Atmel

Mine are all 128-16AU, from two different sellers, adeleparts2010 & sharpseller2000

As a slight aside.

Today it was rather fortunate that I had programmed up a servo cycler on a channel in the TX. There were odd moments when the servo would go erratic. It wasn't the servo or any noise on the TX power rails (already added extra 100 nF capacitors to the 7805).. It turned out to be a temperature sensitive 128. Quick squirt with freezer (minimal charging variety) on the chip cured the problem and a blast from my hair dryer made the fault return. Let's hope that this is a one off with the chips from China....

New 128 ordered at great expense from CPC Farnell rather than trust one from China. Pity things haven't moved on far enough with the M2561.. Another time maybe..

well, I think we will soon find out. Summer is nearly here..

João

Hello and good morning,

I just finished soldering the new M128 and the Rs (i used 470 Ω) to the trim buttons and it works perfectly. Thank you all for your investigations!
I will find out how temperature sensitive my M128 is and do some tests on the battery drain, that was a probem of my last M128 too. But for now it all looks very good

Chris

Great stuff Chris. I won't call you a rock just yet.

I hope the temperature test gives you the green light.

It will be interesting to see what the current drain is with your TX. I didn't measure mine before I changed out the 78L05 for a 7805 up to the point I removed the temperature sensitive chip. I do know that the back of the 7805 was slightly warm to the touch. So I feel that the current draw must have been at a reasonable level.

I believe I saw on the datasheets that the 128A is lower current than the 128. If you have a choice, go for the 128A. From places like Farnell it's cheaper anyway.

Mike.

I think it is normal that the regulator gets warm even at low current drain, maybe due to being regulating from nearly 12V..

João

MikeB wrote:I believe I saw on the datasheets that the 128A is lower current than the 128. If you have a choice, go for the 128A. From places like Farnell it's cheaper anyway..

Farnell was cheaper than those from UK sellers on Ebay. Even better with free postage using the WEBFREE facility.

I scanned through the 386 pages concerning the Atmel 128-16au. I couldn't see any mention of current levels..

João - This was on a TX that is running from NiMh cells. The voltage at the time of the finger test was 9.3 Volts.

From the complete datasheets available through atmel.com
atmega128 17mA typical, 19mA max (page 319)
atmega128A 9.8mA typical, 19mA max (page 321)
These are the currents listed for active@8MHz

-Gohst

I'm looking at the graphs for typical current consumption. I see about 32mA for the 128 at 5V 16MHz and 18mA for the 128A at 5V 16MHz.

Mike.