Opentendo project not working

Discuss hardware-related topics, such as development cartridges, CopyNES, PowerPak, EPROMs, or whatever.

Moderator: Moderators

Post Reply
Victorvisions
Posts: 12
Joined: Sat May 27, 2023 11:03 am

Opentendo project not working

Post by Victorvisions »

Looking for help on an Opentendo build, I’m running out of ideas on where to go from here as I’ve tried swapping around and changing a few things already but still get no image.
The original NES I pulled parts from had a bad PPU (I could get an image everytime on boot up it was just scrambled) so I thought I’d try building a new Opentendo instead of replacing it. I primarily used the BOM to order all new components so figured it’d work no problem but easier said than done apparently. There was a few components I pulled from the original being they were hard to find new replacements for.
Those components were:
* Q1, Q2, Q3
* RA2
* DA1, DA2, DA3, DA4
* U10 (NES lock-out chip was previously disabled on old nes)
* EXP-connector
* U6 (CPU)
* U1, U4 (SRAMS)
* P4, P5, P6
* MOD-RF

I believe I might have burned up the cpu removing it with a hot air gun being the original NES no longer worked after removing it and putting it back in the original with a IC test socket. So I ordered the aftermarket part UA6527 along with the aftermarket PPU UA6528 from a reputable source on eBay. However I do still have the original CPU in case I didn’t burn it up. With this concern I also started to question my SRAMS so I ordered some 16k ones I found online (PN:6116SA120DB) but still no success, once again I did keep the originals. I have ordered the parts for a NULLCIC board too (in case I fried that component as well) after reading some people’s comments about a timing issue I believe? I originally had C6, and C7 installed following the silk screen but later removed them after seeing other peoples builds without them. I reflowed all the solder recently and feel like I have fairly good contact for everything. I went around the board and confirmed with a dmm that all the resistors were installed correctly however have not checked anything else. And finally when I hook it up to my tv I’m using a GBS-control rgb port to get an image so I won’t have color but I also can never get an image, just static.
If anyone has anyone suggestions or ideas that’d be greatly appreciated as I’d love to not see this NES go to waste. Thanks!
Victorvisions
Posts: 12
Joined: Sat May 27, 2023 11:03 am

Re: Opentendo project not working

Post by Victorvisions »

Here’s some photos of the build
Attachments
Solder used for install
Solder used for install
SRAM replacements bought on mouser
SRAM replacements bought on mouser
PCBA in housing with game installed
PCBA in housing with game installed
Tope side of Opentendo PCBA
Tope side of Opentendo PCBA
Bottom side of Opentendo PCBA
Bottom side of Opentendo PCBA
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Opentendo project not working

Post by lidnariq »

What test equipment do you have access to?
Victorvisions
Posts: 12
Joined: Sat May 27, 2023 11:03 am

Re: Opentendo project not working

Post by Victorvisions »

lidnariq wrote: Sat May 27, 2023 12:21 pm What test equipment do you have access to?
I have a DMM and could borrow a Power supply from work and maybe even a oscilloscope if needed.
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Opentendo project not working

Post by lidnariq »

Given a lack of video output:
check if voltages on the CPU and PPU are 5V
check if the 21.5MHz crystal driver is operating at close-to-accurate frequencies
check if the CPU and PPUs' /RESET inputs are high
check if 60Hz and 16kHz are audible (good luck) on the video output pin
User avatar
krzysiobal
Posts: 1037
Joined: Sun Jun 12, 2011 12:06 pm
Location: Poland
Contact:

Re: Opentendo project not working

Post by krzysiobal »

Check for presence of M2 at cartridge output. No M2 might be indicator of broken CPU but also can be a sign that your crystal oscillator produces too low amplitude (CPU is extremely picky about that)
Image My website: http://krzysiobal.com | Image My NES/FC flashcart: http://krzysiocart.com
Victorvisions
Posts: 12
Joined: Sat May 27, 2023 11:03 am

Re: Opentendo project not working

Post by Victorvisions »

lidnariq wrote: Sat May 27, 2023 7:55 pm Given a lack of video output:
check if voltages on the CPU and PPU are 5V
check if the 21.5MHz crystal driver is operating at close-to-accurate frequencies
check if the CPU and PPUs' /RESET inputs are high
check if 60Hz and 16kHz are audible (good luck) on the video output pin
Just wanted to follow up with my results, well I can’t say for certain what my issue was but I think it was perhaps either the 72 pin connector not having good contact or my after market cpu.

Earlier in the week I tried swapping my crystal oscillator back to the oem one from my donar board but had no success in getting video still so today I brought home an oscilloscope. Testing the frequency of the oem one installed I got a reading of 21.473mhz so I was happy with that result and moved on to checking some of my voltage readings.

CPU and PPU both had a reading of 5v and the reset on cpu is high but I couldn’t figure out what pin on the PPU was reset.

I also tried to check the output pin of M2 on the 72 pin connector but got very low readings in the mv so I swapped to the oem cpu and got a high of 2.38v reading on M2 so decided to test my video output again with the current setup and after a few power cycles I got video feed!

I’m currently cleaning everything up and gonna try seeing if I can get a more consistent video feed and if not will perhaps consider buying an oem cpu online.

Thanks for all your guys help with troubleshooting this and any other tips or recommendations are always appreciated!
Attachments
A1D047C5-3048-4559-A5F9-B9802EAEF126.jpeg
5B0686B1-6477-4A44-9D09-6B879215F88A.jpeg
3F5CE20A-8F12-4685-8019-45411B0E8BFE.jpeg
Victorvisions
Posts: 12
Joined: Sat May 27, 2023 11:03 am

Re: Opentendo project not working

Post by Victorvisions »

Ok I almost have my build 100%
So after completing the opentendo I installed a NES RGB 4.0 board and the only issues I’m noticing still is it doesn’t boot up first go every time and then once in any game I’m experiencing a slight slow down in audio (hard to tell if the gameplay is slowed down or not).
And then lastly the edges of my game is not perfectly squared off, and from what I can see of other peoples builds this isn’t normal.
Could all this be caused by the oem cpu perhaps getting damaged during the removal process from the donar board?
Attachments
D2382585-9F56-47D8-A652-3EE82644C60D.jpeg
Post Reply