Late last week, Pramod was able to revive our T.M.N.T. – Turtles in Time PCB. The repair process was extensive, it involved desoldering and validating all of the ROMs and logic chips, socketing and replacing roughly 70% of them with new components, reflowing the entire board. Brandon, one of teams members took time out of his schedule to work on this earlier in the year and I greatly appreciate it!
Even after all of this work, the PCB was still stuck in a watchdog reset. Pramod eventually traced the issue to component 053997, which wasn’t receiving power, and restored functionality by bridging VCC from the neighboring 054253 PAL.
Once the PCB was up and running, I asked Pramod to record audio directly from the CN4 - Sound Out connector so I could implement proper audio gain, confirm what the mix for FM (YM2151) and PCM audio (K053260), and validate mono and stereo output.Over the weekend, I updated our K053260 PCM chip to handle summation and panning of FM audio alongside its PCM channels in both mono and stereo. The FM signals are now routed through the chip’s auxiliary ports, so all mixing is handled internally just like on the original PCB. Getting the stereo balance right was tricky, but it now matches the hardware output.This also means the mix faithfully reproduces quirks from the original hardware, such as the audio “pops” that occur during PCM playback. For example, playing back sound code 82 in the service menu produces two distinctive audible pops in the music, exactly as it does on the original PCB. I’ve included a few comparison recordings from the PCB and core with today’s post for reference.The core has reached a level of accuracy that we are happy with, and we'll resume work on G.I. Joe. This is the closest match to the original hardware I have experienced, surpassing both commercial releases and traditional emulators.
Now that our framework is in place, once we wrap up a few other projects I’ll be turning my attention to audio filtering. The goal is to better capture the character of “analog” playback, since the raw digital output from an FPGA doesn’t fully reflect the way the original hardware sounded.The audio options for the MiSTer version have been updated. You will still find toggles for the audio mix (mono or stereo), FM audio, and BGM/SFX, but now there is also a unified gain control. It has four settings at 25%, 50%, 75% and 100%. This matches the left and right channel volume pots on the original PCB.
I’ve pushed an updated release to update_all (MiSTer) and pupdate (Pocket), or you can manually install it from the attachments below. Updates to Midway Z/Y-Unit platform will be coming soon to the Analogue Pocket soon, followed by the first T-Unit release, NBA Jam. Next week we’ll also see a new Cave 68000 release, Oni: The Ninja Master / Metamoqester, for MiSTer.Disclaimer: All product names, trademarks, and registered trademarks mentioned are the property of their respective owners. "Analogue", "Analogue Pocket", "OpenFPGA", "MAME", "MiSTer", "MiSTerFPGA", "Konami", "Midway", "Cave" and all derivative works are trademarks, registered trademarks, or copyrighted materials of their respective holders. Use of these names does not imply endorsement or association with this post. All rights reserved to their respective owners. This post is for educational and research purposes only.