Thread: Zx81
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Old 14th Mar 2020, 11:15 am   #52
John Earland
Hexode
 
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
Default Re: Zx81

I think I have decided to try the mod described in the blog but could I ask for some clarity?

According to the blog:
"I decided the best approach was to snip that video line from the ULA and divert the signal originally destined for the RF box to the base of my transistor instead. I then wired up the collector to the 5V line and add the resistor to the emitter, the other end of which I earthed on the RF box. I then used a wire to grab the signal from the emitter (prior to the resistor) and threaded this through the spare hole. It was then a matter of unsoldering the RF output wire from the RCA socket and soldering on my composite video wire (coming through the spare hole). Figure 9 shows the finished result. Not pretty but it works!

Okay, so I have a 100R Ohm resistor and I'm waiting for the 2n3904 transisitor to arrive. So, in my language (and I thinking this through in my head) am I correct with the following:

1. Cut the RF line and attach to the transistor's middle pin.
2. Solder the 'collector' side of the transistor to the 5v wire (never seen a transistor so I hope I know which pin is the collector when it arrives!)
3. Solder the resistor to the 'emitter' pin of the transistor and solder the other end to an Earth
4. Solder a wire to the middle section of the TV socket (RCA?) pass this out through the spare hole
5. Solder this wire to the transistor's emitter pin but before the resistor

Could you explain how the position of the resistor in this examples saves the IC?
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