F1C100s DRAM problems - Page 1
Forum section: electronics / general

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 09, 2024, 11:09:58 am
content: After some years I decided to try to solder the remaining F1C100s I had onto the FNIRSI 1013D that had problems and where I failed to solder the first of the two QFN based F1C100s I ordered on Aliexpress.Here is a post about what went wrong the first time:https://www.eevblog.com/forum/testgear/fnirsi-1013d-as-much-use-as-a-chocolate-fireguard/msg4652311/#msg4652311But now with my new camera and low melting point solder paste I thought to give it another try. Set the hot air to 170 degrees Celsius and put the paste on the PCB. It did not went as I hoped, probably due to to much paste. Had to push on the QFN and a lot of solder came from underneath. Took the part of again and cleaned the solder up to try it again. It went a bit better, but it did not align itself like seen on some youtube videos. Had to reheat again and gently push it in it's place.Unfortunately a second pad came loose, this time the read write select signal for the FPGA.All the connections to the QFN seem to be good when inspected with the camera microscope.Carefully made repairs on the missing pads, which also was not easy despite the better zoom of the camera. But I managed, and the core is running. The processor external clock is a reasonably stable 24MHz. (The Rigol scope shows measurement between ~23.8 and ~24.1 MHz and shows the same for the working one.)The only problem I have now is that the DRAM is showing random failures in keeping the data. I'm able to start the FEL code with the DRAM enabled and can read and write to the memory via this channel. After clearing the memory, successive readbacks show random faults in the data. Tried this with 0x00, 0x55, 0xAA, 0xFF and the results are similar. See the attached image.I checked the voltages and they look ok. There is a strange ripple on the 2.5V which feeds the DRAM, but on a working scope it it looks much the same or even worse. The xx0.png image shows the ripple on the problematic one and the xx1.png image shows what it is on a working one.When I start the scope it loads the code from the flash and initializes the display but all it displays is a bit noisy set of bars on the display. See picture below.Can it be that the soldering killed something, or can it be a dodgy chip (it came from Aliexpress), or am I missing something else?

author: Postal2
author_rank: Frequent Contributor
timestamp: December 09, 2024, 12:38:07 pm
content: Quote from: pcprogrammer on December 09, 2024, 11:09:58 amI have experience trying to replace AT91RM9200 from Aliexpress. The chips were good, but I was the fool. Without drying, the chip cracked somewhere inside.

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 09, 2024, 12:48:04 pm
content: Quote from: Postal2 on December 09, 2024, 12:38:07 pmNice picture, but what do you mean with "drying", and how does this relate to my problem?

author: Postal2
author_rank: Frequent Contributor
timestamp: December 09, 2024, 02:04:57 pm
content: Quote from: pcprogrammer on December 09, 2024, 12:48:04 pmSearch with keywords "drying chips before soldering",Quote from: pcprogrammer on December 09, 2024, 12:48:04 pmOpen a topic with the title "I want to learn how to solder" in the beginners section.When something inside the chip cracks from the expansion of steam, it is usually audible, but sometimes it is quiet, you need experience.I usually neglect drying at first when I have a supply of chips and they are not very expensive. But as soon as I encounter a problem similar to yours, the remaining chips are placed on the heater for several days.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 09, 2024, 03:05:36 pm
content: Quote from: Postal2 on December 09, 2024, 02:04:57 pmYou got a kind question, but decided to give a trash answer.Will remember this.Anyway. How are you soldering it? Place only a bit of solder on the ground pad, or the ic will sit high and cause this issues.You might tin both ic and board pads to make it flow easier.Coming fron AliExpress, apply a 50% chance it was defective crap...I've reflowed the F1C200s on my DSO2D10 several times without issues.I kept flattening the solder in the pads when probing the connections with the DMM, causing shorts, but 400°C air and some flux always brought it back to life.

author: Postal2
author_rank: Frequent Contributor
timestamp: December 09, 2024, 03:14:56 pm
content: Quote from: DavidAlfa on December 09, 2024, 03:05:36 pmThat's right. You can re-solder an already installed chip as many times as you want. Everything will change if you take a new one after storage.

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 09, 2024, 03:38:46 pm
content: Quote from: Postal2 on December 09, 2024, 02:04:57 pmWell if you hand spent a couple more words on writing your first post it would have been clear directly that you intended to say "make sure a chip is free of possible moisture before soldering, much like how one needs to dry filament before 3D printing", but I will chuck it up to a not your native language thing.Not sure if this might have been the root of my problem though. The chip has been lying at reasonably normal room temperature and humidity in a drawer in it's original strip packaging for a couple of years.

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 09, 2024, 03:44:09 pm
content: Quote from: DavidAlfa on December 09, 2024, 03:05:36 pmAfter removing the first failure and cleaning the pads, I applied some solder paste on the pads, but most likely way to much. It did flow nicely at low temperature, but like I wrote a lot came squiring from underneath the chip. So removed it again and cleaned of the remaining solder. Added flux and placed the chip back on the PCB. This time it took better, but was misaligned at one end, so had to heat it up again and gently move it into place.After that I used my soldering iron to redo the four sides to make sure the pads were connected.

author: Postal2
author_rank: Frequent Contributor
timestamp: December 09, 2024, 03:50:55 pm
content: Quote from: pcprogrammer on December 09, 2024, 03:38:46 pmI don't solder chips on an industrial scale, but even with my small quantities I can say that this is very likely.Quote from: DavidAlfa on December 09, 2024, 03:05:36 pmI have never received a single faulty chip from AliExpress, except for those I damaged myself. Some simple chips with fake markings had a reasonable amount of defects. I am even writing this on a computer with a processor from AliExpress.In the case of the AT91RM9200, I also encountered an incompatible revision of one of the chips, although the chip itself was working. I couldn't find any information about the revisions, so I bought different ones.I just remembered that when I ordered 2 pieces of AT91RM9200-CI-002 from Aliexpress, the seller directly wrote that they need to be dried. Well, I tried not to dry them and ruined one of the 2 (DRAM interface fell off).

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 10, 2024, 09:49:45 am
content: Quote from: Postal2 on December 09, 2024, 03:14:56 pmI have been thinking about this and find it odd, that it would not be a problem once a chip has been soldered before. If it is about hygroscopic material would it not attract moisture again after being soldered and cause a risk next time round?Or is it about possible moisture in the cavity (if any) where the die sits, that is trapped during production?If it happens does it leave any visible evidence that it happened?

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 10, 2024, 09:54:18 am
content: I don't think it's moisture. Maybe a bad soldering joint?

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 10, 2024, 10:35:39 am
content: Quote from: DavidAlfa on December 10, 2024, 09:54:18 amI have just hit the thing again with 300 degree hot air, but it is still having the DRAM problems.Do you know which memory controller is used in the F1C100s?With a manual I can maybe get a grip on what settings to manipulate to see if it is possible to get it working more reliable.

author: Postal2
author_rank: Frequent Contributor
timestamp: December 10, 2024, 10:40:23 am
content: Quote from: pcprogrammer on December 10, 2024, 09:49:45 amI thought the same 10 years ago and dried old boards completely before soldering. Then I stopped drying them and never had any problems.Quote from: pcprogrammer on December 10, 2024, 09:49:45 amThere are no external marks, but a click can be heard when landing.Quote from: pcprogrammer on December 10, 2024, 10:35:39 amWhen the AT91RM broke, the signals to the DRAM looked fine, it loaded the second bootloader there, but at the moment of starting the code from the DRAM it hung.One might assume that the chips are washed in a bath to make them look better. However, when you choose a seller with an expensive price, it turns out that this "reliable" seller bought the same batch on Aliexpress.

author: Postal2
author_rank: Frequent Contributor
timestamp: December 14, 2024, 05:10:40 am
content: Screenshot from the page for ordering microcircuits from Aliexpress.https://aliexpress.com/item/1005008195168303.html

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 17, 2024, 07:28:50 pm
content: Today I received the F1C200s that I ordered on Aliexpress. (https://www.aliexpress.com/item/1005008145851074.html) Not cheap, but the easiest source for me.I soldered it to the board and that again was a bit of a bumpy ride.At first the SD card and SPI FLASH had bad connections, but due to that it went straight into FEL mode, through which I was able to verify the core was working. After some fiddling with both my iron and hot air, I managed to get it "properly" soldered and it now works. Memory is stable.But, there is always a but, the original problem of the inverse colors on the display is still there.Time for some serious hardware debugging. Have to hook up my Yokogawa scope with 32 channels logic analyzer to the display and see if I can spot the problem, but first measure all the voltages with both a DMM and a scope.

author: Postal2
author_rank: Frequent Contributor
timestamp: December 18, 2024, 01:38:39 am
content: Quote from: pcprogrammer on December 17, 2024, 07:28:50 pmYou have a knack for finding something nasty.Nevertheless, I got interested and bought (cheap):F1C200shttps://www.aliexpress.com/item/1005008183948081.htmlDevboardhttps://www.aliexpress.com/item/1005003479943027.htmlQuote from: pcprogrammer on December 17, 2024, 07:28:50 pmUnbelievable.

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 18, 2024, 06:54:12 am
content: Quote from: Postal2 on December 18, 2024, 01:38:39 amIncluding shipping a bit more expensive than the one I got when mixed with other purchase. Mine is choice item and when total order above 10 euro shipping is free.Quote from: Postal2 on December 18, 2024, 01:38:39 amI bought this one a while back:https://www.aliexpress.com/item/1005004920193384.htmlWas the best deal on Aliexpress I could find on this board.Quote from: Postal2 on December 18, 2024, 01:38:39 amNot everybody can be as great as you when it comes to soldering.

author: Postal2
author_rank: Frequent Contributor
timestamp: December 18, 2024, 08:40:17 am
content: Quote from: pcprogrammer on December 18, 2024, 06:54:12 amWell, you have achievements too. You have already surpassed Tektronix, now you need to surpass Citizen. All you need to do is write a good firmware for this device:https://www.aliexpress.com/item/1005006810392046.html

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 18, 2024, 06:01:29 pm
content: I found the culprit that was causing the colors to be inverted.I checked the voltages and they were a bit high, so I replaced a feedback resistor on the power supply to reduce them, but it made no difference.Did some more measuring near the LCD, where there is a voltage divider (R44/R45 in the schematic of the processor part I draw) and it turned out that the 10K resistor was shot. Replaced it and now it is working fine.Have to see if the other issues of random restarts and dropouts are also gone.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 18, 2024, 07:02:20 pm
content: Nobody needs more useless electronic trash. Just learn the colors... or use the phone.

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 18, 2024, 07:07:48 pm
content: Quote from: DavidAlfa on December 18, 2024, 07:02:20 pmI wrote it has been fixed, so the colors are perfectly fine now. I just saved it from becoming electronic trash. Sure wasted a couple of chips that will end up in the trash, but that is less than a complete scope.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 18, 2024, 07:10:42 pm
content: Ah! My post was for that dumb calculator, not you!

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 18, 2024, 07:13:42 pm
content: Quote from: DavidAlfa on December 18, 2024, 07:10:42 pmAh yes, that makes sense. Best to use a quote next time.

author: Postal2
author_rank: Frequent Contributor
timestamp: December 18, 2024, 07:23:31 pm
content: Quote from: pcprogrammer on December 18, 2024, 06:01:29 pmThis resistor sets the divider for the Vcom voltage. It is not burnt out, it was always like that. But your solution to fix it in software was excellent.Quote from: pcprogrammer on December 18, 2024, 07:07:48 pmAnother brilliant victory.Quote from: DavidAlfa on December 18, 2024, 07:02:20 pmI use a Fnirsi oscilloscope and a calculator would look great next to it (especially with firmware from pcprogrammer).