Amiga 1200 chip RAM repair

Another adventure with my Amiga 1200, recently when booting I was met with a green solid color boot screen instead of loading AmigaOS 3.1 (workbench) as expected. According to boot error color codes that’s most likely bad chip RAM (the first 2MB of RAM shared with custom chips). I burned Diagrom v1.3 on EPROMs using the MiniPro TL866A programmer and installed those in the motherboard ROM sockets. Diagrom outputs diagnostics via serial port (9600 baud 8n1) on the A1200 which I connected to the COM port on my PC running Linux, the output from Diagrom confirmed that the chip RAM was bad.

The Amiga 1200 motherboard

The chip RAM consists of the four chips located close to the center (upper) part of the motherboard, the two ROM sockets are below. Here’s a close up photo of the area with the RAM chips.

Amiga 1200 chip RAM

Amazingly I managed to find the same RAM chips KM416C256BJ-7 sold on eBay, so bought five of them which arrived a week later. These chips are in a SOJ package, directly soldered onto the motherboard, so I used my SMD rework station to desolder the suspected bad chip using hot air, then cleaned up, and added solder.

One chip removed

I soldered in a new chip, but this was apparently the wrong chip, RAM test still failed, but instead of switching back I just replaced one by one until three chips were replaced and I ended up with address line errors in the Diagrom output. This was turning into a nightmare, and I started to doubt the “new” chips were working.

After going over the schematics again I figured out a way to cross check by measuring zero Ohm (connection) on the data lines and address lines between RAM chips using a multimeter, this made me discover several bad solder joints so had to apply more flux and reheat the chips as needed several times before the solder joints were solid. Admittedly I’m a rookie with the SMD rework station (hot air), much prefer the soldering iron, but things started to improve after upping the temp to 380C.

The Diagrom chip RAM test finally went through OK, so I happily assembled the A1200, put the original ROMs back and AmigaOS (workbench) booted fine, but only 1MB of chip RAM was detected. Frustrated, after looking at the schematics again I noticed that the A1200 3.1 ROM will boot (pass tests) even if only 1MB chip RAM is detected (U16 and U17 required, U18 and U19 optional).

I disassembled the A1200 once more and started measuring the data and address lines on the motherboard, all seemed OK. After some head scratching I decided to measure all pins (not just address and data lines), and found out that on U19, one of the RAM chips, the UCAS line (“Upper Column Address Strobe”, pin 28) was not connecting to the board. After soldering pin 28 on U19 manually using my iron the full 2MB chip RAM was detected, and passing all tests. The repair was finally over.

Banned for using VPN

I recently got banned from Reddit with this warning message showing up:

“This account has been permanently banned. Check your inbox for a message with more information.”

Looks like it really is permanent this time. The first time roughly two weeks ago the stated reason was account security related, after resetting the password it worked fine. Now I got banned again for the same reason, but this time the password reset email doesn’t show up. My Reddit account was created in 2017 and not used much, reading content for the most part as opposed to writing. I’m assuming the reason for the ban in this case is because I’m using a VPN (Virtual Private Network), but not completely sure.

I’ve had similar problems with other services using VPN as well, like bank apps on the phone, video streaming through the browser, and more. In some cases the app/service give error message straight that using VPN is not allowed, while in other cases the reason is not obvious at all. The overall trend seems to be that using tools protecting privacy are considered bad in general and should be punished somehow. In this case the choice was easy, skip Reddit while continuing to use VPN, but there are services which would be a lot harder to skip if this trend continues.

Repairing the Amiga 1200 keyboard

Here’s my Amiga 1200, it’s a lot of fun. I use it mostly to play games, program in C language (sometimes 68k assembly) and to connect to the HP 1660AS logic analyzer / oscilloscope through the serial RS-232 port. The nerd specs are; CPU 68EC020 @ 14 MHz (stock), 68882 @ 40 MHz, 2MB Chip + 8MB Fast RAM, RTC, 3.1 ROMs, IDE-CF+4GB, WiFi WPA2/AES.

Amiga 1200 in the lab
Amiga 1200 in the lab

In 2024 I replaced my Amiga 1200 keyboard membrane because some of the keys were failing, bought it from retrofuzion.com which is a good store in my experience, highly recommended.

Amiga 1200 keyboard membrane
Amiga 1200 keyboard membrane

Then a few days ago my shift key on the A1200 keyboard started failing, after taking it apart turns out it was the key plunger (aka key post) for the shift key which was bad, it looks like this.

A1200 key plunger
A1200 key plunger

The black part is some kind of conductive rubber which is what makes contact with the keyboard membrane when a key is pressed, over time (decades) the rubber loses its conductivity which can be checked by measuring resistance with a multimeter.

Bad 1200 key plunger
Bad A1200 key plunger

The bad key plunger as shown is 1511 ohm which is way too high. I found working key plungers on eBay for the A1200 keyboard. After measuring a few of these by now the good ones are usually around 100 ohm, the bad ones over 500 ohm in my experience. After replacing the key plunger with a new one which is 88 ohm the shift key works again.

SecureChatAnywhere ESP32 project

I’m working on a hardware project to be able to use a smartphone to send and receive encrypted messages manually based on my old SecureChatAnywhere project for desktop computers (Java):
https://github.com/modrobert/SecureChatAnywhere

SecureChatAnywhere is a lightweight program written in Java with the purpose of making it easy to encrypt and decrypt any kind of text messages using AES-128/CBC symmetric encryption. The graphical user interface (GUI) is designed as a convenient “copy & paste tool” for computers to manage encryption and decryption stand-alone, in other words without relying on any kind of external communication.

Optimistically I trust desktop computers dealing with plaintext, but not smartphones since they are compromised by design (the cryptographic keys are in control by the vendors). The idea is that the smartphone only handles ciphertext since it is not trusted.

I’m using an ESP32S3 dev kit for the implementation of SecureChatAnywhere for use with a browser on smartphones (e.g. Android or IOS).

ESP32S3 devkit with display

Here’s the C programming progress so far:
[✓] AES-128/CBC with PKCS#7 padding
[✓] http server for ciphertext input and output viewed via browser on the smartphone
[✓] Bluetooth BLE 5.2 HID keyboard host with power save support (this took a lot of time)
[✓] USB 2.0 HID keyboard host
[✓] esp32 I2C display support
[   ] PCB design

All software parts have been tested working individually, I’m now at the stage of combining the software to work together as one. Eventually I will design a PCB and get a suitable case for the project.

New domain and forums

I have registered a domain modrobert.org for the weblog and opened new forums. You are welcome to join. The current forums as listed below:

ʻOumuamua’s light curve

After reading about Avi Loeb‘s proposal to check for radio emissions from the interstellar object ʻOumuamua I had an idea.

What if the tumbling motion of ʻOumuamua based on the observed light curve emitted actually is a way of communicating? I mean that the object was set in a deliberate oscillating motion to deliver a message in the light spectrum using light from a nearby star.

I’m thinking specifically of this part where the light curve is measured:

Source: https://en.wikipedia.org/wiki/%CA%BBOumuamua#Trajectory

Accounting for Vega’s proper motion, it would have taken ʻOumuamua 600,000 years to reach the Solar System from Vega.

Source

Please note that I still doubt there is alien life in the universe besides earth, but hypothetically, if you are going to send a message which takes roughly 600,000 years to reach its destination, how would you do that in practice?

Our modern technology capable of transmitting radio signals only last decades at best, usually even less, so ʻOumuamua producing radio signals seems unlikely. On the other hand, an object launched with deliberate trajectory, certain spin (tumbling in 3 dimensions), which is made from a material where the approximate deterioration in space can be calculated seems more likely even if it’s still a long shot.

ZeroBB – A minimalistic forum on the Tor network

If you have news to report, ideas to share, dislike moderation, and prefer to be anonymous, then read on.

ZeroBB is based on ZeroBin which is an open-source online paste tool where the server has zero knowledge of pasted data. The exception is when you make a new post to the public forum by having “Forum index” checked, the web server will know the key for that post since it is public. The data is encrypted/decrypted in the browser using 256 bits AES.

0bb

ZeroBB is running as a Tor hidden service v3 which means you have complete end-to-end encryption, no HTTPS required (regardless what your browser states). The Tor network also provides decent anonymity, it’s not perfect, but it has great potential.

http://gd6is466quuhsgzbztyv4sjswdhgfii63wf54qsb32v27xmm5dxbtmid.onion/0bb/

The Tor onion URL is long, but it serves a purpose as it also doubles as a key to access the site which in my opinion makes it more secure than DNS. Try to avoid using proxy services to access Tor as it compromises the security (MITM), also avoid services making the URL shorter if you want to keep the post secret. For more info about the Tor network, or to download the Tor browser, check the project site here: https://www.torproject.org/

ZeroBB Features:

  • No moderation.
  • No registration required.
  • No cookies.
  • No database.
  • Post anonymously (comments optionally have nicknames).
  • The user (OP) can delete their post¹ or set initial expiration time limit.
  • Data is compressed and encrypted in the browser before sending to server.
  • Uses 256 bits AES JS library².
  • Search engines can’t index³ the content.
  • Lean and mean minimalistic design.
  • Modified to work over the Tor network.

¹ In order to delete a post and all comments associated with it the “Delete link” URL (token) is required which is given after submitting a new post.
² Check https://sebsauvage.net/wiki/doku.php?id=php:zerobin for more details.
³ As long as search engines don’t execute JavaScript code when crawling (which they don’t AFAIK).

There is no specific direction what this forum is about, personally I like hacking related stuff, programming, reversing electronics and software, and being able share info without being tracked or censored. The forum/board functionality is bare minimum at the moment, pretty far from ideal, but it is work in progress. Let me know if you find any bugs, lots of code is in flux due to active development so expect some downtime.

A solution to global warming after the fact

During dinner today I got an idea how to combat global warming  as a solution after the fact, long after we passed the so called “point of no return”.  My idea is to detonate a bunch of nukes in large uninhabited forest areas on earth which hypothetically triggers a nuclear winter.

Sure, an ice age might not be great, but better than global warming. Besides, what do we have to lose after passing the point of no return and plant life (in effect all life) is dying? If the idea fails, at least humanity goes out with a bang! I wouldn’t have it any other way.

nukes_to_the_rescue