Interton vc4000 power mod
- gozdnijezek
- 3 hours ago
- 6 min read
The Interton Video Computer 4000 (officially abbreviated as Interton VC 4000) is an 8-bit ROM cartridge-based second-generation home video game console that was released in Germany, England, France, Spain, Austria, the Netherlands and Australia in 1978 by German hearing aid manufacturer[2] Interton.[3][4] The console is quite obscure outside Germany, but many software-compatible systems can be found in numerous European countries (see versions of the 1292 Advanced Programmable Video System). The console is the successor of the Interton Video 3001 and was sold for 298DM and discontinued in 1983.[3] From Wikipedia
So I managed to get an Interton vc4000 that was in a sorry state (with all of the wires cut off) and a broken power supply. The transformer has a broken wire on the windings, that would be impossible/very hard to fix. The original power supply provides 15V and 8V AC which makes finding a modern 1:1 replacement a bit challenging, it also uses preoperatory plug. So I started looking for alternatives.
The original power supply provides 15V 230 mA and 8V 600mA AC
Since the first thing after the plug is the bridge rectifier (it transform AC to DC) that got me thinking on how to simplify things. First two things that came to mind were could it be done without any internal modification and if I had to modify the internal parts, how to make it as simple as possible.
So, of course I asked AI:
It will likely not work correctly. While it won't explode or damage the components immediately, the voltages inside the circuit will be too low to operate the console stably.
Specifically, the 8V input line will fail to produce a stable 5V output, and the 15V input line might struggle to maintain the 12V rail.
The Technical Explanation
This happens because the circuit is designed for AC (Alternating Current), which behaves differently than DC when rectified.
1. The Bridge Rectifier Drop
Both inputs go through bridge rectifiers (Br1 and Br2).
With DC Input: The bridge rectifier acts as polarity protection (so you can't hook up plus/minus backwards—it will work either way). However, the DC current must pass through two diodes inside the bridge. This causes a voltage drop of approximately 1.4V.
Result:
Your 15V DC becomes ~13.6V inside the circuit.
Your 8V DC becomes ~6.6V inside the circuit.
2. Missing the "AC Boost"
With AC Input: When you feed AC, the rectifiers and capacitors (C1, C2) charge up to the peak voltage, which is roughly 1.41 x V_RMS.
15V AC ~ 21V DC (internal peak).
8V AC ~ 11.3V DC (internal peak).
With DC Input: You don't get this boost. What you put in (minus the diode drop) is exactly what you get.
Detailed Analysis by Rail
1. The 8V Input (Bottom Rail)
Goal: Produce regulated +5V.
Your DC Input: $8V - 1.4V (diode drop) =6.6V.
The Problem: The voltage regulator (VR2, a 7805) requires an input at least 2V higher than its output to work effectively (this is called "dropout voltage"). It needs at least 7V to output a stable 5V.
Outcome: With only ~6.6V available, the regulator will "drop out." The output will likely sag below 5V (probably around 4.5V) and will carry any noise from the input. The console chips powered by this rail will likely crash or fail to boot.
2. The 15V Input (Top Rail)
Goal: Produce regulated +5V and +12V.
Your DC Input: $15V - 1.4V = 13.6V.
The +5V Regulator (VR1): This has enough headroom (13.6V > 7V). This part will work fine and run cooler than usual.
The +12V Circuit (Transistor T1): This discrete regulator needs an input higher than 12V to function.
With only 13.6V available, you only have 1.6V of "headroom."
While this is technically enough for the transistor to conduct, it is very tight. If there is any load sag, the voltage might drop below 12V, potentially affecting video or audio circuits (which typically use the 12V rail).
How to Make it Work with DC
If you want to use DC power supplies (which is a good idea to reduce heat and hum), you just need to use slightly higher voltages to compensate for the rectifier drop and the lack of AC peak boost.
Recommended DC Inputs:
Instead of 8V: Use 9V DC or 10V DC. (This ensures >7V reaches the regulator).
Instead of 15V: Use 18V DC to 20V DC. (This ensures the 12V rail has plenty of headroom). Note: A standard 19V laptop power brick is often a good candidate here, provided the amperage is sufficient.
Can this circuit be modified to work on just 12V
Yes, this circuit can be modified to work on a single 12V DC power supply, but you have to be careful about how you connect it to avoid under-powering the video chip or overheating the regulators.
Because the ground is common for all outputs (the upside-down T symbols), you can bridge the inputs. However, simply plugging 12V into the existing sockets will result in a voltage that is slightly too low for the "12V" rail.
Here are the three ways to do this, ranging from "Easiest" to "Best Performance."
Option 1: The "Lazy" Bridge (Easiest, but imperfect)
You bridge the two positive input pins together and feed them 12V DC.
How to do it: Connect your 12V DC positive wire to both the "15V~" and "8V~" top pins. Connect the negative wire to the bottom pins.
The Result:
5V Rails: Will work perfectly.
12V Rail: Will drop to roughly 10.5V - 11V. (Due to the diode drop inside the bridge rectifier + the transistor drop).
Risk: The console will likely run, but the video output might be dimmer, unstable, or have audio buzz because the 12V rail is running below spec.
Option 2: The "Internal" Injection (Recommended)
To make 12V work well, you should bypass the Bridge Rectifiers (Br1 and Br2) to avoid losing that precious 1.4V to diode drops.
How to do it:
Open the console.
Solder your +12V DC wire directly to the positive (+) leg of Capacitor C1.
Solder a jumper wire from C1 positive to C2 positive (bridging the two main filter caps).
Connect your Ground wire to the negative (-) leg of C1.
The Result:
You get the full 12V inside the circuit.
12V Rail Output: Will be approx 11.3V (12V - 0.7V transistor drop). This is usually close enough for the system to run stable.
Heat Warning: The bottom regulator (VR2) is now dropping 12V down to 5V (a 7V drop). It will get hotter than it did with the original 8V AC supply. You should ensure the heatsink is clean and maybe add a little thermal paste.
Option 3: The "True 12V" Bypass (Expert)
If you are using a modern, high-quality regulated 12V power supply (like a good wall wart), you don't need the internal 12V regulator (T1) at all.
How to do it:
Remove Transistor T1.
Install a wire jumper between the Collector (top pin) and Emitter (bottom pin) pads of T1.
Feed your 12V DC into the circuit as described in Option 2 (at Capacitor C1).
The Result:
The 12V rail gets exactly 12V (from your power supply).
The 5V rails generate their own 5V.
This is the most efficient method, but only do this if your external power supply is trusted (not a cheap, noisy one), because you are removing the console's internal protection for that rail.
Summary Recommendation
If you want to use a modern power brick, I recommend getting a 15V DC power supply (like a universal laptop charger set to 15V) and using Option 1 (Bridging the inputs).
15V DC provides enough headroom for the 12V rail to work exactly as designed.
It requires no internal soldering or modification to the motherboard.
Just make sure the polarity is correct (though the bridge rectifiers act as a safety guard). I went for the Option 2: The "Internal" Injection (Recommended).
Instructions
Conclusions
It is possible and actually quite simple to power Interton VC4000 off a single voltage and the reason for its original AC dual voltages power supply was probably cost and availability in the 80s. The design could probably be refined a lot, as basically you could replace the whole power board with a modern design, as the whole console runs on 12V and 5V. The 12V is used only for the video generation.
Regarding the current modification I would also say it could benefit from some refinement, since I connected all of the power lines into one, I suspect this contributes to some noise I'm seeing on RF. One 7805 is currently also without a heatsink, I think it could benefit to add one.
Reference:
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