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Tenda S105 5-Port 10/100 Ethernet Switch

Top
Top

Here’s a tiny ethernet switch from the great fle market that is eBay – the Tenda S105. This unit has 5 ports, but only supports 10/100M. Still, for something so small it’s not bad.

Bottom
Bottom

Not much on the bottom, there’s a pair of screw hooks for mounting this to a surface.

Ports
Ports

The 5 ports on the front actually have the pins for the unused pairs of the ethernet cables removed – saving every penny here.

PCB Top
PCB Top

The casing just unclips, revealing the small PCB. Nothing much on the top, just the connectors, isolating transformers & the crystal for the switch IC.

PCB Bottom
PCB Bottom

The bottom of the PCB is a little more busy, mainly with decoupling components. There’s a 3.3v linear regulator to step down the 5v input for the switch IC.

Switch IC
Switch IC

The IC doing all the data switching is an IP175G 5-Port 10/100 Switch from IC+ Corp. No datasheet available for this, but it’s going to be a bog-standard switch.

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STVG-502 Karaoke Machine CRT

Image Display

Here’s the CRT circuitry from a tossed STVG-502 Karaoke Machine, which got a good soaking in Manchester’s brilliantly wet weather before I managed to get hold of it:

Main PCB
Main PCB

I didn’t do a full teardown of this unit, since it was soaking wet & smelled rather badly of sour milk, so instead I quickly gutted it for the useful parts. These machines are a combination of a CD+G player, CRT composite monitor for displaying the CD+G lyrics & a small audio amplifier & 3W speaker. Power is provided from the mains via a transformer, with both 12 & 24v windings. One half of the board has the audio amplifier sections, the other the CRT drive, running from the 12v & 24v supplies respectively. I chopped off the audio section, as that wasn’t needed.

Linear Regulator
Linear Regulator

On this huge heatsink is what I originally thought was the horizontal drive transistor is actually a 12v linear regulator – the board gets fed 16v AC. This is then run through a rectifier which will produce an approx 22v rail, and after the smaller transistor on the left used for power switching. The 22v then gets dropped through a 1/2W 1Ω resistor, then the linear regulator drops it down to 12v for the rest of the circuit – dissipating a goodly amount of power in the process.

Horizontal Output Transistor
Horizontal Output Transistor

This is in fact the horizontal drive transistor, a 2SD613, which according to the datasheet, is intended for audio amplifier output stage applications, not CRT drive. Regardless, it’s an 85v 6A NPN transistor, and does get a bit on the warm side, but was never given a heatsink from the factory.

CRT Drive IC
CRT Drive IC

All the drive signals for the CRT are taken care of by this single DIP IC – a CD1379CP from Silicore. Considering the older CRT-based devices I have, with entire boards twice the size of this one dedicated to discrete components required to drive a CRT, this is definitely an advance in technology. Very few external components are being used, and no custom magnetics.

Video Input
Video Input

The video signal comes in from the CD+G player module on this connector, it’s a standard composite input. The composite video is fed into an amplifier after the controller IC. This video amp is powered from a 140v rail from the flyback transformer, to give enough signal to drive the CRT cathode.

LOPT
LOPT

The high voltage transformer is a BSH8-N5513L, I’ve not been able to find any data on this, but it looks like a standard off the shelf transformer from the listings on the Chinese supplier sites. There are very few support components around here, just a couple of diodes to rectify the high voltage focus supply, and no linearity coil. Weirdly, the 1st accelerating anode of the tube is grounded in this circuit. Very few adjustments are provided, most are set with fixed resistors to keep the cost low.

The CRT

14SX3Y4 CRT
14SX3Y4 CRT

Here’s the CRT, it’s a 5″ monochrome model. I’ve not been able to find much data on this either.

Bent Electron Gun
Bent Electron Gun

Seems the gents in the Shenzhen factory were having a bit of an off day when this one was made – the electron gun assembly is actually tilted in the neck of the tube – as a result the spot formed with no deflection is far from the centre of the screen. This tube does still produce a pretty good picture though, this manufacturing error is easily corrected for with the positioning magnets on the deflection yoke.

Final Mods

PCB Mods
PCB Mods

I’ve installed a couple of mod wires on the bottom of the PCB to get this to work outside the original application, without the room heater of a linear regulator in circuit this will run fine from a 12v supply. The PCB quality is a bit naff – even quick heating with a soldering iron makes tracks fall off the laminated paper board.

Image Display
Image Display

Image quality is surprisingly good for the cheapest CRT-based monitor I’ve ever seen, I figured a Fallout reference was required here; anyone for a proper CRT-based PipBoy? 😉 Shame the phosphor isn’t green.

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Blog Housekeeping & More Of The Same

Since I’ve been working on the backend servers a lot over the past few days, I’ve decided it was time to get some broken things on the blog fixed.

Firstly, the radiation monitor graphs. Originally I was using a Raspberry Pi to grab the data from the local monitor, and that was connecting via FTP to the server over in the datacentre to push it’s graph images. Since the server is now on the same local network as the monitor, there’s no need to faff about with FTP servers, so I’ve rejigged things with some perl scripts from cristianst85 over on GitHub, running on the web server itself.
I deviated from the suggested place to put the scripts on the server & opted to store everything within the Experimental Engineering hosting space, so it gets backed up at the same time as everything else on a nightly basis.

This is also accessible from the menu at top left, the script pulls data from the monitor & updates the images every 60 seconds via a cron job.

I’ve removed a couple of dead pages from the blog system, along with some backend tidying of the filesystem. Over the years things have gotten quite messy behind the scenes. This blog is actually getting quite large on disk, I’ve hit the 15GB mark, not including the database!

Caching is enabled for all posts on the blog now, this should help speed things up for repeat visitors, but as most of my content is (large) image based, this might be of limited help. I’m currently tuning the MySQL server for the load conditions, but this takes time, as every time I change some configuration settings I have to watch how things go for a few days, before tweaking some more.

Server Control Panels – More Of The Same

Sorry Sentora. I tried, and failed to convert over to using it as my new server control panel. Unfortunately it just doesn’t give me the same level of control over my systems, so I’ll be sticking with Virtualmin for the foreseeable future. Sentora stores everything in, (to me at least), very odd places under /var/ and gave me some odd results with “www.” versions of websites – some www. hosts would work fine, others wouldn’t at all & just redirect to the Sentora login interface instead. This wasn’t consistient between hosting accounts either, and since I didn’t have much time to get the migration underway, this problem was the main nail in the coffin.

Just storing everything under the sun in /var/ makes life a bit more awkward with the base CentOS install, as it allocates very little space to / by default, (no separate /var partition in default CentOS), giving most of the disk space to /home. Virtualmin on the other hand, stores website public files & Maildirs under /home, saving /var for MySQL databases & misc stuff.

The backup system provided is also utterly useless, there’s no restore function at all, and just piles everything in the account into a single archive. By comparison, Virtualmin has a very comprehensive backup system built in, that supports total automation of the process, along with full automatic restore functionality for when it’s needed.

Sentora did have some good points though:
It handled E-Mail logins & mail filters much more gracefully than Virtualmin does, and comes with Roundcube already built into the interface ready to use. With Virtualmin the options are to use the Usermin side of the system for E-Mail, which I find utterly awful to use, or install a webmail client under one of the hosted domains (my personal choice).
Mail filtering is taken care of with Sieve under Sentora, while Procmail does the job under Virtualmin.

Sentora does have a nicer, simpler, more friendly interface, but it hides most of the low-level system stuff away, while under Virtualmin *everything* on the system is accessible, and it provides control interfaces for all the common server daemons.