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Author Topic: Cheap scope with LCD  (Read 7065 times)
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I have to do a bit of complaining for this product. I must say that this product has one big flaw to be sold as kit.

I've got my set, soldered first side, checked voltage according to manual, soldered another side, powered it on and what?

On LCD everything looked ok. Booted, all controls responded properly, frequency measurement worked perfectly. But signal was in form of flat line across upper half of the screen. Nothing was able to move it.

What next?

If it would be nice kit I would have documentation! Poor printout of schematic and layout is not enough. There should be a description and some reading in addition to that C14 reversed. Something like "assemble voltage converter to power opamps, check voltage on test point this and that, it should be whatever, solder another few elements, check something else"... Soldering everything on kit and powering up is a recipe for disaster. And for some people 30 bucks for couple hours of soldering is too much to just burn it!

That happened in my case. Some bad element in power converter was probably wrong. Maybe opamp. Obviously I have no idea what it could be now after all chips seem to be burned. Test points for power to opamps? 12V DC? maybe +/- 12V? Who knows? My knowledge is not as good to just look at schematic and know what voltage would be where and what exactly is happening. But I don't this kit is only for people that do know.

When I powered the unit and started to look what can be wrong it was not giving correct signal out of TL084. Some voltage was present, but not 500hz waveform that was coming in (my multimeter has frequency measurement). Another half of TL084 used in conjunction with AtMega to vary voltage out of it was probably also damaged. After couple plays with buttons my flat line is gone. ADC was getting 6-7+ V in. Probably adjusted too much out of TL084 and it burned.

What I have now? Working AtMega and lcd with menu. Almost zero chance to find bad elements to fix it in this smd nightmare with this kind of poor documentation.

Yes. Documentation is key to make from pile of parts and PCB a good kit worth your money. You sell kits so people can learn from them not only to solder some SMD resistors but how everything works. They should have chance to avoid disaster before it happens. If you're able to design this kind of equipment you could spare couple additional hours to write about it.

Why you're putting test points for something when there is zero information what should be on them? You don't solder kits by "solder everything on one side and check power". What next? Maybe there is no smoke when you power it on? You should assemble it with documentation in logical blocks, check proper operation for each one so one fault would not take down everything after it.

Scope is nice. For that price point is great event not workink smiley-wink But manufacturer should spend some time to make proper documentation for that, so people can have more chances to have working device. Charge few bucks more for that paper, I don't mind. It will be worth it.

What should I do next? Order bunch of parts from digikey or mouser, spend money for parts, shipping and try to fix it? Burn some more experimenting? Order another kit and try from scratch? Order it assembled? I don't know (I'm looking forward to your advise).

I know that it was first kit I've made that I don't like just because of that documentation.

Btw. Sorry for my English. I'm still trying to learn it.
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I feel your pain!

This KIT is definitely not suitable for "getting started" with electronics or SMD soldering. If the ATMega and the display is still working, maybe you can get jyetech to send you a set of replacement parts containing all the remaining stuff.

It's hard to tell what may or may not have been fried. If you desolder R24, you can isolate the ADC from all the opamp stuff. Then you could feed the ADC with a small DC voltage (0-1V) and see if the horizontal line moves up/down if you vary the voltage. This will be independent of all the switch positions. If the ADC still works you can leave it alone for the time being and check the opamp stuff (supply voltage, aplification factor...). If you've reversed D1 (zener) the NE5532 opamp should survive the short to GND, as it has short circuit protection on its output. just replacing the diode (or reversing it) should help.

If you've reversed D7, the opamps won't get a negative supply voltage and will not work.

The 500Hz test signal is created by the ATMega64 cpu itself, so if that doesn't work.... if you switch it to frequency measurement mode, all the opamps are bypassed and it should be able to measure frequency no matter if the opamps are dead or not.

I've posted some pictures of the correct orientation of the diodes on the seeedstudio.com support forum. there is a thread for the jyetech scope.
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johnny126:

Thank you for let me know this great forum (and others from here). I feel sorry for the difficulties (poor documentation increased these difficulties) you encountered when assemlbed the kit and agree to most comments you made to the documentation of the scope. The documents definitely need to be improved. Especially they should contain contents specific to beginners. We will make plan for revison of related documents and do that as soon as we can.

For the unit you have now I would like to make some suggestions for troubleshooting it. Since LCD and all keys are working the digital portion of the unit are ok. The problem is in its analog portion that includes analog power supplies, opamps and ADC. Here are a few steps you can follow:

Please first check AV+ and AV- with a volt meter, particularly the AV-. AV- should be -6V or lower if you use a power supply of +9V or higher. If AV- is close to 0V then you would not be able to see any traces. For AV- problem please check:
 
1 ) Is D7 placed correct? - D7 should be placed with its striped end pointing 7805. If D7 is placed wrong Q1 is likely be burnt. Q1, if burnt, can be replaced with any general purpose PNP transistor  (even a through-hole one).
2 ) Is L2 open? - Please check it with multimeter. It should read about 3 ohms.
3 ) Any possible short/open of components around Q1 and Q2?

AV+ is not very critical. Any value from +6v - +15V will be ok. AV+ is directly from input of power supply via an inductor. So its value should only slightly lower than power supply voltage(+VRAW).

If AV+ and AV- both are OK and there no trace seen then you can check ADC (TLC5510).

1 ) Do not connect any input signal. Check voltage at its pin 19 with a multimeter. For a normal ADC if this voltage falls between 0.6V to 2.6V trace should appear on screen. If the voltage is out of the range try to change V.Pos to see if it can be brought into the range. If not check soldering/values of opamps and related components.

Since the opamps can withstand up to 30V between their pos and neg power supply pins they are not easy to get burnt.

2 ) Check voltages at pin 16 (17) and pin 22 (23) of 5510. They should be about 2.6V and 0.6V, respectively. If they are far from these values then the chip is bad.

3 ) If voltages about are all normal and still no trace on screen then check ADC connections. Power the unit off and check connections between 5510 and Mega64 with a ohmmeter. These connections include the 8 data lines (pin 3 - 10 of 5510) and clock line (pin 12 of 5510). Please use a sharp probe tip and check from pin to pin (not from soldering pads). This is try to uncover any bad soldering (possible opens/shorts). Since the pins are small vision check are un-reliable.

If all above are good but still no trace displayed then a scope is needed to do further investigations. Or replace the chips. Anyway please first try the steps stated and let me know what you get.

We encourage users write us regarding to any problems/issues in using/assembling the scopes. We will do our best to help.
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Thank you madworm.

My AtMega still works (the most important part smiley ). I'm planning to order the rest of the chips and some other components (transistors, diodes) and go with replacement after isolating specific parts of the circuit.

Can you check for me what should be the voltage on AV+ & AV-? I'm pretty sure that this is the first part that is wrong on mine.

I'm not starting with electronics. I just didn't expect to be left with kit that have to be soldered in one shot (almost) with zero information about common failures or information to debug the circuit.

But as the last EEVBlog says, when it doesn't work it is the best way to learn electronics smiley
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Thank you for posting JYE Tech smiley

Very helpful.

I bought the assembled unit and the kit and was very satisfied.

Is it possible to modify the PCB to use the cheaper ATMEGA644P-20AU TQFP-44 at 20MHz with 32 IO pins or one of the new ATXmega chips?

It might be extremely helpful to put the ATmega chip on a small daughtercard so it can be easily swapped out.
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Thank you JyeTech for all information. I'll try to debug this circuit and I'll post any results that I have.

I'm looking forward to get the new documentation.
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gnu_linux:

Thank you for suggestions! We will consider that in future modifications.
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This is cool I have been looking for something that I could put in my pocket and use on automobiles to test the signals to the computer on the fly. I can't wait to get mine. I hope that someone will build a box for it as some of my other bug build units look nasty and are a problem without the case. Finding a good case is a real pain. I used makeup containers in the past but they have gotten so small.

Any feed back from fellow readers about good cheap cases would be nice. I like the ones I can find at the dallor store. A portable soap box is one of my favorates.

Thanks all,
Hugh
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A question regarding firmware update...
I built myself a Mega ISP to update the formware, downloaded the files for the 080 version from the manufacturer's web site and ran the following .BAT file:

<
Code:
avrdude -P com5 -c avrisp -b 19200  -p m64 -U lfuse:w:0xAE:m -U hfuse:w:0xC0:m -U efuse:w:0xFF:m
avrdude -P com5 -c avrisp -b 19200  -p m64 -U eeprom:w:113-06201-080.eep -B 100
avrdude -P com5 -c avrisp -b 19200  -p m64 -U flash:w:113-06202-020.hex
avrdude -P com5 -c avrisp -b 19200  -p m64 -D -U flash:w:113-06201-080.hex

No matter how I set the fuse for EEPROM clear safety, I always get:


avrdude: verifying ...
avrdude: verification error, first mismatch at byte 0x0000
         0x13 != 0x00
avrdude: verification error; content mismatch


when trying to write the EEPROM. Everything else updates OK, however, the scope is not really working.

Can anyone offer advice?

Best,
    Jens
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Solution to the EEPROM problem posted on the seeedstudio forum.
Fill the eeprom manually using terminal mode...

Best,
   Jens
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awesome!
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I just completed assembling the DIY kit.  I had to put some washers under the front panel to get the push button switches to work freely.

I agree most people should not attempt this kit due to the SMD parts and the limited documentation.  I think the solution to the kit would to have a partial kit with all the SMD parts mounted like the ATmega64.

Update: www.jyetech.com now has a DIY kit with all SMD soldered on for $40 USD.

My kit came with 70 series firmware which I upgraded using a USB to TTL adapter.  Works great.

I am greatly impressed with this kit!
« Last Edit: July 25, 2009, 12:25:53 pm by mlindeblom » Logged

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Some of the SMD resistors are easily manageable, but for some reason others are a bit tiny. I wonder if that was a matter of cost or availability. I don't know if the smallest parts are 402 (didn't measure them), but that's about the smallest size I can handle with tweezers and soldering iron. I managed to misplace/drop two of those and had a hard time finding them again.

Soldering the ICs is by far the easiest part. I'd even go as far as saying that I would have preferred soldering all the chips myself. All the tiny resistors is what takes hours.
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• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

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to be really useable and not another toy you'dd need at least an external trigger... latest firmware support external trigger, but you do need to solder resistor and there is no entrance stage nor connector...
I really hope they'll create a new version featuring a good external trigger/or a second signal output.

great product otherwise... I'dd prolly buy the kit with all SMD already soldered if they'll add it to seeedstudio or sparkfun...
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They have the all SMD presoldered now.
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• Upload doesn't work? Do a loop-back test.
• There's absolutely NO excuse for not having an ISP!
• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

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