6560/6561 related oscilloscope and vectorscope images

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lance.ewing
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Wed Jun 22, 2016 3:58 pm

@eslapion
Do you happen to know what resistance value your variable luminance resistor is set to? i.e. the one labelled R10 in the s-video mod instructions here: http://sleepingelephant.com/denial/wiki ... deo_output

And does your board have the R8 and R9 resistors as shown on that wiki page? And if so, do they have the values shown, i.e. 240 for R8 and 510 for R9?

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 22, 2016 11:26 pm

lance.ewing wrote:@eslapion
Do you happen to know what resistance value your variable luminance resistor is set to? i.e. the one labelled R10 in the s-video mod instructions here: http://sleepingelephant.com/denial/wiki ... deo_output

And does your board have the R8 and R9 resistors as shown on that wiki page? And if so, do they have the values shown, i.e. 240 for R8 and 510 for R9?

I made my own S-Video mod in a very different way than suggested. Note: This is a VIC-20 with PET style keyboard I am using here with a very early serial number.

Since I had a spare 6560-101 (I didn't want to risk damaging the original 1981 chip), I removed the original chip, installed the spare and bent out the chroma pin from the chip. I directly soldered a surface mount sized (1206) capacitor to that pin, soldered in series a 360 Ohms resistor and fed that directly to a female S-Video connector installed inside the computer.

The board shown in the S-Video mod is the VIC-20cr so most of the parts shown in there don't even exist on my board.

Also, the VIC-20 with PSK has a tiny inductor that acts as a noise filter which doesn't exist on the VIC-20cr. IMHO, this gives it the very best video output of all VIC-20 revisions.

The solution proposed by A4000bear is a good approach if you have a VIC-20cr and your 6560/61 is soldered to the board, neither of which is true for me.

The video amplifier of the VIC-20 with PSK comprises about double the number of components of the VIC-20cr and is shown here: http://www.zimmers.net/anonftp/pub/cbm/ ... 4001_1.gif

Potentiometer R10 is replaced with R7 and is normally adjusted so the pk-pk amplitude from black to white is slightly less than 1V. As shown in earlier captures, the amplitude measured was 928mV which is perfectly acceptable. The VIC-20 with PSK also has another pot R32 which doesn't exist on the VIC-20cr and its function is to adjust the DC offset of the common emitter amplifier. R8 and R8 are replaced with a transistor current control system (Q6).
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Fri Jun 24, 2016 12:47 pm

To be honest, I don't think I need to know what your variable resistor value is currently set to (or whether its there or not). After analysing the circuit for a bit, I've realised that it doesn't even matter what your equivalent of the R9 resistor is either. The important fact is that you're seeing roughly 3V for White. The White colour is unique in that it has no pull down within the 6561E (and presumably the 6560). So that simplifies the circuit a bit. It means that you can theoretically pick any pull up and pull down resistance values in this simplified voltage divider, as long as the output voltage between them is 3 volts for White.

So I could pick 510 or 470 or whatever, and then calculate what the variable resistor would need to be set to in order for the output voltage to be about 3V. I realise that the circuit is a little bit more complex than this, but I'm hoping that I can view it in this simplified form for the purposes of helping with my analysis of the Luminance section of the die shot, which I hope to post several posts on later this evening.

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Fri Jun 24, 2016 2:51 pm

@lance.ewing
That's not quite true.

You also have to make sure the blanking (black is identical luckily for us) level to white level is slightly below 1V p-p.

You have to adjust the amplitude first, then the DC offset to get white to 3V.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Fri Jun 24, 2016 3:09 pm

I notice that you have 928 mV for the value between black/blanking and white. I've also noticed that the s-video mod instructions say this:

The variable resistor, R10 will still function, allowing you to adjust the luminance level as before. If you have an oscilloscope, adjust this resistor to give a Y signal level of 1 volt from sync tip to white, while your monitor is connected.

Firstly, when it says "sync tip", what does it mean? Is this the bottom of the sync pulse, or does it mean the top, i.e. the black/blanking level?

Your measurements show that the value between black and white is 928 mV, but the value between the bottom of the sync pulse and white is (correct me if I'm wrong) 928 mV + 350 mV = 1278 mV. The s-video mod instructions suggest that the variable resistor can be tweaked to adjust the gap between these levels, but I'm not actually sure if it is talking about the bottom of the sync dip, or the top.

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sat Jun 25, 2016 7:59 am

@lance.ewing
"tip" is ambiguous at best.

I tend to have more faith in the Commodore service manual than public wikis especially since this is only a copy/paste from a forum thread.

The S-Video mod wasn't scrutinized by a qualified video technician.

I have a Blu-Ray player which is one of the very few pieces of equipment I have left on which I could display to S-Video an SMPTE bars and tone reference to compare but it would be a ton of trouble getting a scope attached to that!
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby Tom » Wed Jun 29, 2016 9:04 am

I don't think this has been covered yet: is it possible to confirm or deny that in non-interlaced mode vertical sync ends halfway across a horizontal scan?

I'm daring to imagine that this explains the ostensibly off-by-33 line counter — it's a count of 65-cycle periods since vertical sync ended.

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 29, 2016 10:37 am

Tom wrote:I don't think this has been covered yet: is it possible to confirm or deny that in non-interlaced mode vertical sync ends halfway across a horizontal scan?

I'm daring to imagine that this explains the ostensibly off-by-33 line counter — it's a count of 65-cycle periods since vertical sync ended.

I closely examined the horizontal blanking interval in the previous captures, I guess it's time to switch to the vertical one...
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby Tom » Wed Jun 29, 2016 12:17 pm

eslapion wrote:
Tom wrote:I don't think this has been covered yet: is it possible to confirm or deny that in non-interlaced mode vertical sync ends halfway across a horizontal scan?

I'm daring to imagine that this explains the ostensibly off-by-33 line counter — it's a count of 65-cycle periods since vertical sync ended.

I closely examined the horizontal blanking interval in the previous captures, I guess it's time to switch to the vertical one...

Cool. My current best guess model is that the horizontal counter and vertical counter have no direct link to one another. If the non-interlaced display has a vertical sync that ends on the half-line then that makes the model consistent.

Also if your scope can easily record the number of lines between sync and the first non-border line then that would also resolve whether vertical sync logically goes at the beginning or end of a field, though it's probably somewhat academic.

If you were in possession of a PAL Vic, which I think you're not (?), would that be compatible with your equipment?

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 29, 2016 1:45 pm

Tom wrote:Cool. My current best guess model is that the horizontal counter and vertical counter have no direct link to one another. If the non-interlaced display has a vertical sync that ends on the half-line then that makes the model consistent.

Also if your scope can easily record the number of lines between sync and the first non-border line then that would also resolve whether vertical sync logically goes at the beginning or end of a field, though it's probably somewhat academic.

If you were in possession of a PAL Vic, which I think you're not (?), would that be compatible with your equipment?

I do have a PAL VIC-20 (purchased from MCes a few months ago) and I will try to give you all the information you want concerning the VBI but right now I'm on a mad rush. Canada Post is about to go on strike and I must churn out as many orders as quickly as I can.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby Tom » Wed Jun 29, 2016 1:49 pm

eslapion wrote:I do have a PAL VIC-20 (purchased from MCes a few months ago) and I will try to give you all the information you want concerning the VBI but right now I'm on a mad rush. Canada Post is about to go on strike and I must churn out as many orders as quickly as I can.

You're doing another huge unrewarded favour; I'll be grateful whenever. Thanks!

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 29, 2016 1:56 pm

Tom wrote:You're doing another huge unrewarded favour; I'll be grateful whenever. Thanks!

This darn scope which cost more than 2k$ back in 2003 is mostly busy collecting dust on the top shelf of the electronics workbench.

It has to be put to good use every now and then for purposes other than proving Jens Schönfeld is wrong...
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Fri Jul 01, 2016 2:38 pm

I'd love to see any information regarding the PAL VIC as well. As you know, the one and only die shot we have is from a PAL 6561-E, so anything we learn from external measurements of a PAL system should in theory be discoverable inside the die shot.

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sun Jul 10, 2016 5:09 pm

Awrite... over the last few weeks I was faced with chaos in my sales because of the Canada Post labor dispute and battling a medical problem with my left ear.

Can someone be kind enough to give me a recap of the captures I was supposed to do for you guys ?

I'm really sorry I let you down but 3 visits to the doctor as well as daily medication and all the stuff involved in dealing with postal problems with my customers took their toll. Add to that the guy who stole me a PLAnkton module.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby a4000bear » Mon Jul 11, 2016 7:13 am

lance.ewing wrote:I notice that you have 928 mV for the value between black/blanking and white. I've also noticed that the s-video mod instructions say this:

The variable resistor, R10 will still function, allowing you to adjust the luminance level as before. If you have an oscilloscope, adjust this resistor to give a Y signal level of 1 volt from sync tip to white, while your monitor is connected.

Firstly, when it says "sync tip", what does it mean? Is this the bottom of the sync pulse, or does it mean the top, i.e. the black/blanking level?



Sync tip refers to the bottom extremity of the sync pulse. In a correctly terminated video signal, the voltage between black level and maximum white level is 700mV. The level between the sync tip and the top of the sync signal (which is black level) is 300mV. Add the two together and you get 1V for the complete video signal. Note that these values are for PAL. There are some slight variations for NTSC which the attached drawing does not fully show.

When a video signal is modulated onto an RF carrier for transmission, the video signal is inverted, making the sync tip the highest voltage level and white level the lowest voltage level. This is why it's called 'sync tip'. This inversion is done to help reduce the effects of interference on the received TV picture, and is used on all TV systems apart from the original 405 line system as was developed for use in the UK in 1936.

PAL.gif
PAL.gif (5.62 KiB) Viewed 415 times


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