Converting 405 lines to 625 lines using a Hedghog II
 

I like to make it clear from the outset that this thread relates only to the Hedghog II. The original Hedghog has not got the hardware to do 405 to 625.

In August 2019 Jeffrey Borinsky successfully built a 625 to 405 standards converter. He detailed how he did it in a thread on Golborne Vintage Radio Forum.
The big thing was that he found a way to use a video decoder that was designed for 625/525 lines only, to successfully acquire a 405 signal. This was a big development and has allowed me to write new firmware for Hedghog II which will allow it to convert from 405 to 625 as well as doing 625 to 405.
No change to hardware is required just a firmware upgrade

Jeffery was able to make the SAA7118 video decoder in his converter lock to 405 lines by under clocking it. I tried under clocking the TVP5150 in a Hedghog II and it worked.But the data clock from the TVP5150 had too much jitter in it to give good results. However I found that over clocking it worked much better and produced a data clock clean enough for Hedghog II to use.

When in 405 to 625 mode its data clock is close to 35 MHz which is quite a bit above its normal 27 MHz.
To date it has been tested in a number of Hedghog II and each one worked well with the TVP5150 showing no signs of distress or any sort of ill effect.
But as the TVP5150 is working so far outside its normal operating area no guarantee can be given firstly that every TVP5150 will work and secondly that if it does work that it wont be damaged.
In my opinion I think that the TVP5150 will be OK but as I have said no guarantees.

I have no suitable VCR to record/playback 405 lines so I don't know how well it will preform with a VCR as source.
If someone does try it with a VCR I would be interested to know how it worked. So maybe you could post here with the results..

I have uploaded new firmware to the Hedghog web page which allows a Hedghog II to work as a 405 to 625 converter as well as converting from 625 to 405.

Stephen forum member Freya is supplying fully constructed Hedghogs

Frank

Re: Converting 405 lines to 625 lines using a Hedghog II
 

From memory the Hitachi VT11 and the Ferguson 3V29 was ideal for this purpose, the DOC sometimes cut in unexpectedly, as far as I remember it went well with them, and they were a common machine, good luck in finding one.

Re: Converting 405 lines to 625 lines using a Hedghog II
 

Hi Tony,
On the 3v29, the DOC gets in the way producing a ghost image half way across the picture on 405 line playback.

I spent some time trying to bypass the part of the video IC that deals with the DOC. In the end, I just grounded the DOC output pin (or input pin, I can't remember now) on the chip & that cured the problem.

Apart from that, it works very well in 405 mode.

Of course for 625 playback, it's very noticeable without the DOC functioning!

Cheers
Nick

Re: Converting 405 lines to 625 lines using a Hedghog II
 

For those sufficiently confident with VCR circuitry, the ability to switch drop-out correction on for 625 and off for 405 sounds like a useful mod.

Re: Converting 405 lines to 625 lines using a Hedghog II
 

Mitsubishi HS-M60V makes a superb 405 machine. Plays back and records beautifully.

Re: Converting 405 lines to 625 lines using a Hedghog II
 

Thanks for the information on the video recorders and disabling the DOC.

Frank

Re: Converting 405 lines to 625 lines using a Hedghog II
 

Frank's design works fine when the input is a 405 line signal from a very steady source (like a 625 - 405 line converter Big Grin), but unfortunately the 405 line video signal from my VCR won't work.

Especially, as probably expected, the horizontal sync goes haywire.


Jac

p.s. my VCR is a Sharp VC-M300

Re: Converting 405 lines to 625 lines using a Hedghog II
 

Hi Jac
Thanks for testing and letting us know.
I had feared that might be the case if there is jitter on the line sync from the VCR.
I have no VCR myself to test

Frank