Re: 6569 luminances

From: Gerrit Heitsch <>
Date: Sun, 13 May 2012 22:16:15 +0200
Message-ID: <>
On 05/13/2012 09:22 PM, wrote:
>> It's only 2 transistors, a 1N4148, some resistors and 2 capacitors.
> Accidentally having diagram at hand?

Sure... I think I posted it before, but a bit of ASCII-graphics won't hurt:

Video amp for TED or VIC-II. To be used in place of the RF
modulator, generating better signal quality.

Note: This circuit removes the CVBS output! It's Y/C only!

                    ___ R1
   chroma in  -----|___|---+     +5V
                           |      |
                           |      |
                    R2     |      |
                    ___    |    |/
              +----|___|---*----|  T1
              |                 |\
              |   R4        R3    V
              |   ___       ___   |
              |         |
              |         |        || C1
             ---        +--------||---------- chroma out
             GND                 ||

               D1       R5    +5V
                       ___   |
   luma in ---|<|--*--|___|--*-------------------+
                   |         |                   |
                   |         |                   |
                   |       |/                   ===  C2
                   +-------|  T2                 |
                           |\                    |
                             V                   |
                             |   R6        R7    |
                             |   ___       ___   |
                                       |         |
                                       |        ---
                                       |        GND
                                       +--------- luma out

  T1 = T2 = BC547B
  D1      = 1N4148
  R1 = R2 = 510 Ohm
  R3      = 68  Ohm
  R4      = 270 Ohm
  R5      = 470 Ohm (TED manual suggests 1 KOhm)
  R6 = R7 = 150 Ohm
  C1      = 1nF
  C2      = 100nF

Do _not_ use metal film resistors, keep connections short.

luma in    = pin 23 on TED, pin 15 on VIC-II
chroma in  = pin 13 on TED, pin 14 on VIC-II

luma out   = pin 1 on video output
chroma out = pin 6 on video output

These 2 video amps might work on other outputs if they are designed as

Chroma: The output is open source and should be terminated with 1 KOhm
         to GND

Luma/Sync: The output is open drain and requires an external pullup

>> A while ago I did an experiment, using 3 1N4001 diodes I limited Vdd of the 6569R5 on my test board to about +10V instead of +12V. The chip still worked fine, including the color output, just got a bit less hot.
> Interesting idea - I haven't tried that. You put a divider there or something more sophisticated?

No, just 3 diodes in series between +12V and pin 13 of the 6569R5. Each 
diode will kill between 0.6 and 0.7 volts.

If the voltage goes too low, one of my 6569R3 will still run, but 
produce a black/white picture, the chroma circuit no longer working 

>>> Yup - those were IMHO the best boards. With lots of unused space though. Mine (the one I refer to) is 250425. I keep it because it is a) the original first I bought and b) it is customised, with practically everything socketed, etc.
>> Now you only need to replace 2114 color RAM with a CMOS version
> I have never thought of/measured it - is the difference worth the effort?

The original 2114 is NMOS and gets noticably warm. The CMOS-Version 
(LC3514A or MB8414) does not. A few milliamps here, a few miliamps there...

>>   and the 7805 and 7812 with state of the art switching regulators and you're set.
> Yup, with the VIC working at lower temp and other power savings it might pay, I guess. Have you done this with yours? If yes, then what parts you used?

I have replaced the 7805 on one of my C16 boards with a RECOM 
R-78B5.0-1.5 and the onboard 7805 on a 250407 with a RECOM R-785.0-1.0. 
They stay cool and need no heatsink. They are quite expensive though, 
about 10 Euros a piece, so don't expect them to pay for them with the 
power you save. I do it to have less heat inside the box.

Replacing the 7812 as well can be done, but it's questionable since it 
doesn't produce that much heat. The VIC is the biggest load on it and it 
needs about 40mA at +12V.

If you can't get the RECOM regulators, you could look for the clones 
made by 'TRACO POWER', their equivalent is called 'TSR 1-2450' for the 
+5V part and is the same size.


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Received on 2012-05-13 21:00:05

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