Cheapmod Mini - a brand-new Cheapmod-based modchip for the OG Xbox

[SylverReZ]

 

The Cheapmod Mini is a modchip in a small form-factor for the Original Xbox. Based off the Cheapmod schematics, the chip comprises of a single 49LF020 (256k) LPC flash to fit (1 x 256k) custom BIOS.

Features:

• 256k LPC flash fitted for (1x256k) custom BIOS (e.g. Cerbios).
• Boot imports, backups and DVDs region free.
• Running unsigned code such as homebrew.
• Installation of a custom dashboard (e.g. UnleashX).
• Easy to upgrade the HDD (no HDD locking required).
• Very easy to install - via pin header or by soldering directly to the motherboard.
• Low-cost and affordable.
• Free and open-source.

Disadvantages:

• Works only for 1.0, 1.1 and 1.6 mainboards.
• 256k can only be used to fit one custom BIOS.

Diagrams can be found here on the SylverReZ website: https://m4x1mumrez87.neocities.org/cheapmod

Will be released on my main GitHub at: https://github.com/m4x10187

Edited February 11 by SylverReZ

[SylverReZ]

An update regarding the order of my final revision PCBs, they arrived by Royal Mail in a really posh blue box with JLCPCB branding. I never thought that the chips would be the same size as a small coin (so bizzare). One current problem that I'm facing at the minute, is that the later 49LF020 'A' and 'B' variants do not work with the cheapmod according to a user on XBOX-SCENE in relation to the address bus bug. I am scowering places to find genuine old stock chips before I can test any further, this will be a big investment of course because no other supplier except marketplaces such as eBay will sell them. I will be avoiding AliExpress and cheap Chinesium fakes of the 49LF020, as they usually are resurfaced 49LF020A/B chips.

Edited July 11, 2023 by SylverReZ

[DobaMuffin]

The cheapmod works due to an address bug in the 49lf020 in which it will accept any address as a valid address and will happily send the data requested. This hardware bug was fixed on the 49lf020a/b variants and thus no longer worked with them. On 1.0 and 1.1 units, it was as simple as grounding d0 and wiring it up to the lpc interface. On 1.3-1.4, you had to reconnect the lframe signal from the mcpx to the lpc header since the lframe signal is only present on those board revisions for the 1.2 units, and those were development units only containing an mcpx x2 chip. Interest for the cheapmod grew again when the 1.6 came out since the xyclops used the lpc interface to boot the console, and thus all of the necessary signals for a cheapmod were present on the board. This required rebuilding the lpc interface on the 1.6 motherboard and cutting the lframe signal going to xyclops so that there would be no contention for the bus as the xyclops didn't see any valid memory read cycles.

Of course, all of these issues were solved when basic modchips like the aladdin came out. They created their own lframe signals for the flash chip on board, and they also fixed the memory addresses so that is was also in a valid range for the flash chip. They also dealt with lframe or d0 by grounding them on boot to disable the onboard tsop flash, or to cancel the lframe cycle for the xcyclops.

[SylverReZ]

Just now, DobaMuffin said:

The cheapmod works due to an address bug in the 49lf020 in which it will accept any address as a valid address and will happily send the data requested. This hardware bug was fixed on the 49lf020a/b variants and thus no longer worked with them. On 1.0 and 1.1 units, it was as simple as grounding d0 and wiring it up to the lpc interface. On 1.3-1.4, you had to reconnect the lframe signal from the mcpx to the lpc header since the lframe signal is only present on those board revisions for the 1.2 units, and those were development units only containing an mcpx x2 chip. Interest for the cheapmod grew again when the 1.6 came out since the xyclops used the lpc interface to boot the console, and thus all of the necessary signals for a cheapmod were present on the board. This required rebuilding the lpc interface on the 1.6 motherboard and cutting the lframe signal going to xyclops so that there would be no contention for the bus as the xyclops didn't see any valid memory read cycles.

Of course, all of these issues were solved when basic modchips like the aladdin came out. They created their own lframe signals for the flash chip on board, and they also fixed the memory addresses so that is was also in a valid range for the flash chip. They also dealt with lframe or d0 by grounding them on boot to disable the onboard tsop flash, or to cancel the lframe cycle for the xcyclops.

Thanks for the well descripted info.

[DobaMuffin]

No problem. It's all info I've gathered over the past few years, either through discussions with people, independent reading of old articles and books, or through research into the cpld code for open source modchips.

[SylverReZ]

Just now, DobaMuffin said:

No problem. It's all info I've gathered over the past few years, either through discussions with people, independent reading of old articles and books, or through research into the cpld code for open source modchips.

You're very helpful with all of this stuff in mind. Right now, I am currently working on a 1.6 revision diagram for the Cheapmod Mini, after it was reported that installation was 100% possible.

[DobaMuffin]

Yeah. I believe I was the one who mentioned it was possible tbh. I know I've done it on my personal consoles before. It's very simple. Take an lpc rebuild board, install it, and then cut a certain trace on the top of the motherboard near the xyclops chip to cut lframe going to it.

[SylverReZ]

Attached are 1.6 diagrams for the cheapmod. My own diagram will be place onto my website once its fully done.

[SylverReZ]

 

 

Edited July 12, 2023 by SylverReZ

[SylverReZ]

A limited stock of Cheapmod Mini chips will be sold on eBay, its unclear when these chips are going to sell but time will tell. These chips will be programmed with any BIOS you want, as long as it sticks to the 256k range - Cerbios, X2, M8+...

Edited January 30 by SylverReZ

[SylverReZ]

 

[SylverReZ]

Ladies, gents, and everybody of all genders. I am finally happy to bring you the repository to Cheapmod Mini.

https://github.com/m4x10187/cheapmod-mini

[SylverReZ]

If your Cheapmod Mini isn't working due to fragging, even though you've installed it correctly, then it could be down to a voltage issue. Make the following modifications as shown in the diagram. If your chip works fine, then this is not needed. So far no cases of fragging have been discovered from my testing, but it can happen unexpectedly.

[SylverReZ]

Finalized gerbers for Cheapmod Mini v2. Let me know if there are any issues with the PCB; I have thoroughly checked the traces and everything seems to be in order.

BOM:

U1: SST49LF020-PLCC32

C1 - 0.1uF 0603

PPTC062LFBN-RC (for the connector)

cheapmod-mini-v2-final.zip

Edited February 11 by SylverReZ