BillC

It's a voltage regulator, similar to the 78xx series.

The SIO connector is similar to multiple coaxial connectors integrated together. The outside of the coaxial plug is male but it also has a female socket in the center, while the corresponding coaxial jack is female with a male pin in the center.

The information that AliExpress asked for may be something new, but I didn't see any good reason to provide it and a good reason not to. I ended up ordering the parts I wanted for an ASUS 1215N from eBay, only CDN$2.50(<US$2) more than same items from AliExpress.

Another thing about AliExpress, when I signed up and tried to purchase some items they want copies of my ID, credit card, and credit card statement, just my credit card information and home address is enough for eBay and Amazon. Since I've had a friend have an issue with identity theft, and what they requested could be used for this, I declined to send the information and cancelled the order.

The new regulator is a switching type that is probably generating some ripple/noise. Checking the +5V output with a DMM set to AC volts should give you a reading of how much ripple is present.

If you set your DMM to AC volts when connected to the DC output it should give a reading of the AC ripple, the range will need to be adjusted since this should be low.

The US Doubler upgrade consists of replacement firmware and a double height IC module to increase the size of the 6810 RAM buffer. The CPU is not modified.

@Nezgar: The ROM socket is likely a type of zero insertion force(ZIF) socket, pulling out the end piece would unlock the pins for easy IC insertion/extraction. This one appears to be a low-profile version, most ZIF sockets are much taller.

I checked my 8bitclassics cable and it does match the connections from my previous post, both red and white RCA plugs connect to pin 3 of the DIN5M plug.

This cable only needs 4 output connectors for dual audio, s-video on the mini-DIN, composite should be yellow, and red/white should both be mono audio. Perhaps it was wired incorrectly, check continuity between the RCA plugs and the DIN plug. Yellow should connect to pin 4, red/white to pin 3.

If you're interested in upgrading RAM the U1MB upgrade eliminates the need for MMU/BASIC chips, plus a lot of other features.

@Michael: I see that you used an original 2364 Rev.C BASIC ROM, just thought I'd point out that the 600XL PCB Revision you used is able to be rejumpered to accept a 2764 EPROM. The socket has to be changed/extended using the existing 28-pin footprint as well.

According to an article I found 1.44MB media needs to be demagnetized by a bulk eraser before they can be formatted at 720KB. Depending on the age of the mechanism density can also be set either 720KB or 1.44MB by switch/jumper, or automatically by the HD sensor. Later 3.5" mechanisms may also have dropped support for 720KB media as a cost cutting measure, eliminating the sensor for HD media recognition and configuring the mechanism to operate only in HD mode. I did say my 1.44MB Sony mechanism is from the early 90's.

Some 1.44MB 3.5" mechanisms will work with the XF551. When I purchased a CSS 3.5" mod for the XF551(early 90's) it came with a Sony 1.44MB mechanism that works when used with 720KB 3.5" discs, the ones that do not have the extra hole indicating HD. It is also supposed to be possible to use 1.44MB media by wiping them with a bulk eraser and covering/plugging the HD sensor hole(or other method of disabling HD media recognition).