Golborne Vintage Radio

Just been doing a little more work on this and I have noticed that with a 525 line source the the output looks a little woolly when compared with a 625 line source.
With a 525 line source some artefacts can be seen before and after any vertical lines. Horizontal lines are not affected. 
The source that I am using is a test card from another Hedghog PSC. Viewed on a monitor the 525 and 625 line test cards look equally good and sharp.
I know that this test card can be a bit harsh but it is not causing any problems at 625 lines.
As it is only vertical lines that is effected what ever is causing this must be in or around the decoder.
The converter should only effect horizontal lines.

It does not photo easily but I have tried. Photo below.

Frank

Looks like under and overshoot on the photo.
Or ringing.

Hi Trevor.
That's a good description of what it looks like.
I must have a look at what filters the TVP5150 uses. From memory I think some are switchable.

Frank.

Well that was a fruitless time spent with that. I eventual tried a different 525 line signal source and it is fine.
It must be down to the harshness of the card.

Frank

I don't think the testcards that you generate in a Hedghog have strict bandwidth limiting. I know it's ultimately limited by sampling frequency but it may still upset the filtering in the decoder chip.

Hi Jeffrey
As you have said the test card is only limited by the video clock frequency. There are some transitions from mid grey to/from peak white and even some peak white to/from black which just takes one cycle. This is far from ideal.
I had thought that it would effect 625 and 405 similarly but there you go.

Frank

Reminds me of the time I was doing some work on standards converters years ago. I was getting odd results with crosshatch. Turned out that the generator had it's interlace backwards. So the white line on the 2nd field was above the 1st. This completely fouled up the interpolation.

Worst part was that I had designed the crosshatch generator.

Another happy Hedghog user. I just (finally) finished getting my Hedghog (MkI) completed and its now working very nicely, after a few hiccups.

The fine soldering was taken carefully and steadily with lots of flux from the flux pen, and the smallest solder I could find. It came out very nicely, especially after a nice clean-up with flux remover. Surprisingly, soldering in the tiny 32-pin chip using "drag soldering" (under a microscope) was virtually the easiest bit to do. The tiny resistors on the other hand had to be watched like a hawk, otherwise they tried to head for the hills (or under the bench, mostly). The tiny 6-pin analogue switch IC proved a bit fragile. Trying to remove a solder splash between pins I instead removed a pin! RS came to my rescue with relacement chips quite quickly and cheaply.

Worryingly, the kit was dead with very high current draw (>500ma) on switch on, despite the rails testing fine (about 1K across the 5V rail), but after a lot of testing, examination and desoldering, I finally desoldered the modulator chips and the fault(s) vanished. The problem turned out to be fake Chinese modulator chips, proved by seeing good composite video with the chips removed. Both chips tested identically faulty, with 200-300mA current draw each when probed outside the board with a 5v psu (+5v on pin 15, 0v on pin 16 if you need to check).

Chris Wood quickly came to my rescue with replacement modulator chips which were duly soldered in . The device finally worked after an initial heart-stopping moment with no output before we realised that the DIP switches were not yet set correctly!

So yet another huge cheer for Frank C for this lovely design. Well done, sir!

-Jeremy

Hi Jeremy
Well done on successfully completing it.
I find the analogue switches the hardest to solder. There is not much on them to hold while aligning and soldering them. It can be difficult to see the pin 1 mark and if some flux gets on top of the case nearly impossible to see it. 

I had one modulator with the same problem as yours. The rest of the pack of 10 that it came in were OK.
My method of fault finding was a bit crude. I left it powered up current limited at 1A for a short while.
A finger to the case of the modulators revealed which one was faulty.

Happy viewing with your Hedghog
Frank

Leave it powered up like that and it will desolder itself from the PCB!

If I want another Hedghog I know that I'd just buy one from Stephen Evans rather than play around with SM assembly.