Re: 6569 luminances

From: Gerrit Heitsch <>
Date: Mon, 14 May 2012 12:56:55 +0200
Message-ID: <>
On 05/14/2012 12:23 PM, wrote:
> On 2012-05-14, at 07:37, Gerrit Heitsch wrote:
>> He... considering that the original circuit was an image published on the website. I just made it into ASCII so it can be easily posted.
> Your ASCII-art skills are remarkable in this context.

Thank you... Took a while to do it though as wasn't much fun in 'vi'.

Here's the link to the circuit from the original posting:

Further on in the thread they got more fancy with tries to eliminate the 
vertical bars generated by the 8565. Since I only wanted it for a 6569 I 
used this simple stage of the evolution.

Remember that this ciruit will only produce a Y/C-Signal. If you want 
composite, you'll have to add a capacitor of a few hundred pF between 
Chroma and Luma. Ideally this is done in the plug and not on the board 
so you can still use Y/C for monitors that have the proper input.

>>> Tried what works better in such case? Or is it 470 for VIC and 1k for TED?
>> So far I have only built one for a C16 and there the 470 Ohm seem to work.
> Have you noticed tangible improvement in picture quality?

For the C16 not much changed. This could be 2 reasons:

1) The modulator doesn't mess with the signals too much.

2) The PCB layout of the C16 board is broken, Chroma and Luma signals 
run side by side for quite a bit of distance. This results in enough 
Chroma being coupled into Luma that you get a color picture if you just 
connect the Luma signal to the monitor. I did cut the Chroma trace and 
ran a direct wire which did help some.

>>>> Do _not_ use metal film resistors,
>>> Why?
>> Because they are a metal film with a spiral groove in it. Which is sufficiently close to a coil that it will act as one once the frequency gets high enough (This circuit goes up into the MHz range). The effects are not very big but enough to influence the picture quality.
> I see, thanks. But this applies not only to metal film. Carbon film, wire, ... , doesn't it? So I guess the safest bet is a carbon comp. or similar.

I used the cheap carbon film resistors, the ones sells for 
less than 2 Euros per bag of a 100. No problems.

My first ciruit used a 1 KOhm precision poti instead of the 2 510 Ohm 
resitors in the Chroma part. This allows you to adjust the level. Was 
able to turn it down to zero and get a black/white picture. One needs to 
be careful though since just using a poti will allow you to overdrive 
the transistor or overload the driver in the VIC if you turn it the 
other way too far.

> Thank you Gerrit! I truly appreciate your inputs and willingness to share and help.
> BTW. I checked again the temperatures of the elements. Next to VRs and VIC, the next biggest "heat offenders" are SID and PLA. I even placed some self adhesive radiators on them some years ago. Especially SID gets really hot. Then the next is CHAROM. Don't know why. BASIC doesn't get so hot. But this makes me think about this +12V you took down to 10.. Since both boiling plates (VIC and SID) use the +12, would lowering it in general allow SID still to work but dissipate less heat? Would it have any adverse effect elsewhere? Shall have to check..

The ROMs run on +5V only, so messing with +12V won't help them. The SID 
uses the +12V for some of the output stage and since it's analog, 
changing the voltage might change the sound. So be careful what you do. 
Unless I missed something, the +12V are only used for 6569 and 6581.

As for the ROMs... you could desolder all of them, and add a little 
adapter with a 74LS11 and a properly programmed 27C256 on it. Then you 
have all 3 ROMs in a single CMOS-EPROM which needs a lot less power, 
especially if in standby (_CS high).


- Build an adapter to use a 27xxx-EPROM in the socket of a 24pin 2364 
ROM. Most of it is 1:1, just a few lines need to be rerouted. Do not 
connect the _CS line directly. Place it either into the KERNAL or BASIC 

- Connect all 3 _CS signals for the ROMs to the 3 inputs of one of the 
gates of the 74LS11. The output goes to _CS and _OE of the EPROM.

- Also connect two of the _CS-Signals to A13 and A14 of the EPROM.

The 74LS11 is a 3-input AND gate. So when the CPU wants to talk to one 
of the 3 ROMs, one of the inputs of the AND goes LOW, resulting in the 
output going LOW and activating the EPROM. Which part of the EPROM gets 
selected is also done by 2 of the _CS lines. You just need to put the 8 
K BASIC and KERNAL and the 4 K char into the right parts of the EPROM. 
The 8 K block where A13 and A14 are both low stays empty.


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Received on 2012-05-14 11:00:35

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