The vLA81 is a modern plugin replacement for the ZX81 ULA. It is one of several ULA replacements I have made for members of the Sinclair computer family including the vLA82 for the Spectrum 48K, the vLA128 for the Spectrum 128K (Toastrack) and +2 (Grey case) and the vLA1 for the Sinclair ZX Interface 1.
As they simply don't make ZX81 ULAs anymore, then unfortunately if the ULA has failed (and there's not much else on a ZX81 to fail), then options for repair are rapidly diminishing. The vLA81 provides a simple way to keep these icons of 80's computing going.
Apart from providing the functionality of both the earlier 2C158E/184 ULA (without back porch) and the 2C210E (with back porch), the vLA81 also has a few extras added.
vLA81 features:
- Fits within the same 40 pin DIL socket outline as the original ULA.
- Narrow IC pins for easy plugin ULA replacement. In most cases the existing socket will be OK (unless, of course, the existing ULA is soldered in).
- Provides the same functionality as the 2C210E Sinclair ULA.
- Video level selectable between standard video (suitable for direct connection to a 75 ohm monitor input) and high sync level (suitable for the modulator input or some video mod boards).
- Back porch on/off select.
- Internal 32K memory support (High or Low for the different hires schemes).
- Programmable user configuration gives access to:
- Inverse or normal video and choice of black or white border.
- 50/60 Hz video standard.
- Ability to map ram to the ROM space (write protect enable/disable – 32K internal ram required).
- Tested with an extensive suite of ZX81 software.
- Ideal for preserving the original ZX81 ULA.
- Low power consumption.
Whether you want to just get a faulty ZX81 back up and running, or want to extend the ZX81 with expanded memory and HIRES, the vLA81 can provide what you need.
Customer Reviews
I needed a replacement ULA as it failed after trying to fit a ZX Wespi MCU to an old ZX81. I ordered the vLA81 and it worked straight out of the box. I must say that I was pleasantly surprised in how quickly it was delivered from NZ to the UK.
Well Done! all round.
Ferranti ULAs are said to fail at some point due to excessive temperature rise on the chip itself. Mine had not suffered from that yet, but I could not keep my finger on it long without burning it. The replacement uLA81 works perfectly.
The additional benefit is that you can connect pin-16 to the composite video input of a monitor for high picture quality. So, you can get rid of the RF modulator.
In my case, it saved a bit of time for building a buffer amplifier to be able to use pin-16 of the original Ferranti ULA.
After living in various lofts from 1985, I finally got round to getting it out and trying to power it up! It worked perfectly when I put it away, but now initially all I could get was a very blurred "K" eventually going to a white screen. I recapped it , no better. Also at this point broke the keyboard cable! Sio new keyboard and composite mod was next, still nothing ram pack off or ramp on. Got a used replacement VLA from Ebay, this worked for short periods but eventually the 81 crashed. Saw the VLA81 and decided one last go to resurrect, it arrived no problem from NZ and I plugged it in, hallelujah a perfect "K" cursor, soak tested it for 24 hours no problems. Now written many Basic programs and upgraded to internal 16K, all good many thanks VRetro.
perfettamente funzionante
Used this to replace a dead ULA on an 'Issue 3' board. I had to desolder the original and replace it with a socket, but once I'd done I installed the vLA81 and switched on. It was great to see the ZX81 back to life! Of course my next project is now to install 32k RAM...