Cheap scope with LCD

http://www.emachinetool.com/new/catalog/vertical.cfm?ProductID=719

It's good enough for small PCBs and other odd jobs. There are even CNC mods for it. I haven't tested it with metal though. The nice thing about it is that it's really small and portable and not too expensive.

Looks nice thanks :slight_smile:

I've been able to make it crash with the 070 firmware and a clean power supply. I've checked with my big scope that the ADC chip doesn't get any clock signal form the ATmega64 anymore when it is crashed. That could explain why the screen shows nothing anymore or at least doesn't get any updates. I've also confirmed that the CPU is only rated up to 16MHz (ATmega64-16AU) but it is clocked with 20MHz in the scope. Maybe this one doesn't tolerate 20MHz and gets upset.

To make sure it's not caused by bad solder joints, I've touched up all the pins of the ATmega and the ADC chip, but that didn't improve things at all.

I will make one last attempt to fix it by replacing the CPU hoping it works. If that doesn't help I will salvage some parts (display, switches, ADC) and the rest will go into the TRASH.

Mine seems to have the ATmega64-16AU and a 20MHz crystal.

Most components can tolerate a slight overclock, but who knows.

I suppose you could try to use a native 20MHz part and see if it works better :slight_smile:

Well, the 20MHz ATmega644 chips are all TQFP44 as far as I can see and I'm not going to make a new PCB for that thing.

I've checked with my scope that the "dead" buttons actually work. The signal gets to the chip, but it doesn't react. The ADC chip doesn't have a busy line or some sort of protocol, so it shouldn't be able to freeze the CPU (unless it short some pins). It could be the ADC chip, but as I also get corrupted fonts on the screen sometimes, I think it must be the CPU. Once I have a replacement ATmega, I will cut all lines to the ADC and see if it still crashes. If that's the case it simply must be a bad processor. I also could try to see if the ADC still works when the program has freezed by injecting an external clock to it and scope the data output lines for a change.

It simply has to be the damn cpu...

They should have made it field replaceable.

Oh well :frowning:

It's good enough for small PCBs and other odd jobs. There are even CNC mods for it.

This is something I've wanted to do for a while. I searched and the CNC mods seem to just be a few people who have done it and posted pictures with a general idea. Do you know of any specific plans or better yet complete conversion kits?

At least for the short term, I'm looking to cut/engrave project enclosure panels. The machine you linked might be a bit small for that. though.

Thanks

The machine indeed is SMALL, not much larger then a common food processor.

You can buy CNC enabled version of this here: Note | Hinweis | Nota | Let op | Nota | Serveur surchargé

They also have bigger ones for more serious task and ones with longer x-travel. Of course they cost more than just 300?. Last time I checked, you could also get an upgrade KIT for it. Unless you want this particular machine, I'm sure you can find similar ones on your continent. As with every piece of machinery, good stuff ain't cheap.

I got mine Saturday and am having fun with it. The display is a bit dim for my old eyes but otherwise it works fine.

I've been trying to find a schematic for the beast but haven't had any luck. Can someone point me to one?

The DIY KIT contains a schematic. It's a bit low quality as small colored text was rastered on the BW laser printout. I could scan it when I get back home. Its pretty simple and straight forward. The only "nifty" stuff is the negative voltage creation for the opamps (at least from my point of view).

The DIY KIT contains a schematic. It's a bit low quality as small colored text was rastered on the BW laser printout. I could scan it when I get back home. Its pretty simple and straight forward. The only "nifty" stuff is the negative voltage creation for the opamps (at least from my point of view).

That would be great! Thank you.

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 :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.

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.

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.

Thank you madworm.

My AtMega still works (the most important part :slight_smile: ). 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 :slight_smile:

Thank you for posting JYE Tech :slight_smile:

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.

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.

gnu_linux:

Thank you for suggestions! We will consider that in future modifications.

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

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:

<

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