Retro SSTV Anyone? II

Where it all started as far as most are concerned and saw heavy use from the 60s through to the 80s. Colour and Hi-res modes have unfortunately pushed this system into the backwaters of SSTV. Time to resurrect interest in this simple analogue system.

Re: Retro SSTV Anyone? II

Postby Steve Anderson » Fri May 05, 2017 9:34 pm

Semis, even those from the 60s are very reliable as long as there have been no other failures, e.g. the power supply. I would go looking for dry joints, open-circuit pull-up/pull-down resistors, switches where contacts are dirty/tarnished, pots whose wipers don't contact the track...and so on. But there is close on 100 chips in there so it is possible that some may be sick. This is going to be a labour of love I think!

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Re: Retro SSTV Anyone? II

Postby Klaas Robers » Tue May 09, 2017 5:47 pm

Good to tell me. I almost ordered several memory IC's, because there are vertical lines in the grey scale picture that obviously don't have to be there. But your remark reminded me that ALL IC's are placed in sockets. The sockets of that age were not too good, so I decided that it will be bad contacts. The yourney to my home couldn't be good for it. But I am going to search for the bad contacts rather than just removing the circuits and placing them back. I get already more and more familiar to the circuit details.

I should make a photograph of the disturbed picture as it is now, just for reference.
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Re: Retro SSTV Anyone? II

Postby Steve Anderson » Tue May 09, 2017 6:30 pm

Ah yes! I'd forgotten you mentioned all the ICs were in sockets, another area worth looking into. Pull them out, a squirt of contact cleaner, replace them and see if that improves matters. It's unusual that in what is really a consumer level product has IC sockets. For configuring 50/60Hz operation etc a few jumpers would have been enough rather than bending IC pins. A bit of a botch really. It's probably too early a design for DIP switches.

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Re: Retro SSTV Anyone? II

Postby Steve Anderson » Tue May 09, 2017 6:32 pm

Klaas Robers wrote:I should make a photograph of the disturbed picture as it is now, just for reference.

Yes, a reference point is always useful to be able to judge your progress. Relying on (your) memory is always risky. Especially if someone else comes along with similar problems and wishes for some guidance.

Recall in the MkI up-converter I had a RAM problem where I had faint, but noticeable vertical lines, I'm glad I took before and after photos for reference and comparison. At the time I put that down to a slightly slow RAM on some bits, but it may have been simply replacing the RAM chip cleaned the socket contacts. And that was a new socket!

It could have been the IC pins too, we'll never know. Soldering is usually very reliable but when developing a prototype sockets are almost imperative. They really don't have a place in a production product...they also add cost...and unreliability...as you may be finding out now.

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Re: Retro SSTV Anyone? II

Postby Klaas Robers » Tue May 09, 2017 8:23 pm

I made a photo of the monitor screen. As you (will) see, this version displays a dotted picture. I think this is to mask artifacts of propagation delays. May be I can try later to undo the dotting by bending two pins of an IC outside its socket.

This should be a 4 steps grey scale, but you see that vertical lines are visible instead. It is not easily seen where the fault is, because the Robot uses Gray code inside and converts this to binary just prior to D-A conversion. I think this is done because there is no true synchronisation following the ADC, the changing value is snatched into memory. Then Gray code is an advantage as between two steps there is always just one bit changed. So the error is never more than one grey step.

The grey scale is generated as four digital values and stored into memory, so the ADC is not yet in the chain. The Gray codes are:
Black: 1000
Dark : 1111
Light: 0111
White 0000
I am going to check the "Data In" and "Data Out" of the 16 RAM chips, with the scope synchronised to the line sync.

The Robot has another anomality: four horizontaly successive dots are stored in four different chips. The result is that the address can be kept stable for 4 successive dots while the data outputs are muliplexed to construct the video out signal. This explains vertical white lines, a line comes out of a certain chip. You can see: the white lines have a spacing of exactly 4 dots.

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Edit (Andrew Davie): Image resized and placed inline. Original image still available as link.
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Re: Retro SSTV Anyone? II

Postby Klaas Robers » Wed May 10, 2017 7:36 am

I did the Data-In - Data-Out test for the 16 memory IC's. Firstly it is strange to see that after you have written a 1, you read a 0, and if you wrote a 0 you read a 1. That explains the mysterious 7404 inverters in the 4 data out lines (U57 and U58).

But unhappily I found 6 of the 16 memory chips to be defective. At least it looks like that. The Data-Out is always a 0 (for one chip) or a 1 (floating, for the other 5 chips) The position of the defect in the picture moves when I change the position of the chips. Strange enough all 4 LSB chips were defective, one MSB-chip was defective, which caused the bright white lines in the black bar, and one chip in the bit 1 row was defective.

I have now exchanged the MSB eroneous chip for a working bit1 row chip, which almost removed the white lines. The next photo shows the result. I also "switched off" the dotting, indeed by bending two pins (9 and 10) of an 7400 (U104) out of its socket.
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Re: Retro SSTV Anyone? II

Postby Steve Anderson » Wed May 10, 2017 1:24 pm

Progress indeed. 6 out of 16 chips defective is an unusually high percentage, and grouped together in generally one area of the array. The hard part may be getting replacements.

I've downloaded the datasheet for them, they're unusual in that they're in 22-pin DIP packages - I've never come across 22-pin devices before. 20-pin, yes, 24-pin, yes, but never 22.

Correct, the 411s invert the data, you write a 1, a 0 comes out...odd again (See datasheet).

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Re: Retro SSTV Anyone? II

Postby Andrew Davie » Wed May 10, 2017 1:39 pm

Steve Anderson wrote:Progress indeed. 6 out of 16 chips defective is an unusually high percentage, and grouped together in generally one area of the array. The hard part may be getting replacements.

I've downloaded the datasheet for them, they're unusual in that they're in 22-pin DIP packages - I've never come across 22-pin devices before. 20-pin, yes, 24-pin, yes, but never 22.

Correct, the 411s invert the data, you write a 1, a 0 comes out...odd again (See datasheet).

Steve A.


Perhaps this is a source... http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=UPD411
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Re: Retro SSTV Anyone? II

Postby Klaas Robers » Thu May 11, 2017 12:48 am

There are not UPD411 in thi9s board, but MM5280N-5 chips. I found a source on Ebay that had 12 pieces and I ordered 8 of them. But I am going to test the ones I have one by one, by placing them in a properly working position / socket. Then I can see that the problem is definitely in the chip, as a good chip works in this position. It might not be impossible that a previous owner placed the not working chips in the row of bit 0, as this is not so annoying in the picture. I have hardly information on the history of this box.

Yes, they are 22 pins, same pitch but slightly wider than the usual 14, 16, 18 and 20 pin packages. And there are sockets for them !

I keep you informed.
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Re: Retro SSTV Anyone? II

Postby Klaas Robers » Thu May 11, 2017 4:28 am

I did the one-by-one-replace-test, that is replacing one by one the suspected chips to a MSb position socket and indeed: five chips gave white lines in the black bar (output is always 1) and one chip gave black lines in the white bar (output is always 0). I left them out of the Robot 400 and stored them in a kind of chip grave yard. They are definitely checked as died.

Then, when I replaced the original IC in this position the MSb worked again fine. Now I am waiting for the replacement chips..... The arrival date is foreseen to be 23 May - 16 June. We'll wait........
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Re: Retro SSTV Anyone? II

Postby Steve Anderson » Thu May 11, 2017 4:18 pm

Good, that's narrowed down most of the faults (we hope). What's left after that we hope will be simple or even better, nothing at all!

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Re: Retro SSTV Anyone? II

Postby Andrew Davie » Thu May 11, 2017 4:47 pm

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Re: Retro SSTV Anyone? II

Postby Steve Anderson » Thu May 11, 2017 8:07 pm

Yes, I might be too, if it were not for the fact they don't ship to Thailand. It says. "No power to unit." Probably just needs the rear breaker pushing in, or something simple in the power supply. What all that 'stuff' is on the left-hand side of the front panel is...anyone's guess. It also is a 115V/60Hz unit, possibly plugged into 240V. This could have also fried many of the chips as well as the PSU.

So not only would the PSU need fixing in addition to fried semi's but conversion to 240V/50Hz and EU standard SSTV. You really want to (need to) have one to accept one in this potentially bad condition. If I were to buy it and if I could fix it I would make it switchable between EU and US line/frame rates and 120/128 lines (if possible).

I think I would wait until a better example came along, i.e. I would pass on this one...even at their asking price...

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Re: Retro SSTV Anyone? II

Postby Andrew Davie » Thu May 11, 2017 10:04 pm

Steve Anderson wrote:Yes, I might be too, if it were not for the fact they don't ship to Thailand. It says. "No power to unit." Probably just needs the rear breaker pushing in, or something simple in the power supply. What all that 'stuff' is on the left-hand side of the front panel is...anyone's guess. It also is a 115V/60Hz unit, possibly plugged into 240V. This could have also fried many of the chips as well as the PSU.

So not only would the PSU need fixing in addition to fried semi's but conversion to 240V/50Hz and EU standard SSTV. You really want to (need to) have one to accept one in this potentially bad condition. If I were to buy it and if I could fix it I would make it switchable between EU and US line/frame rates and 120/128 lines (if possible).

I think I would wait until a better example came along, i.e. I would pass on this one...even at their asking price...

Steve A.



Stuff on the front left is remains of a "property of..." sticker, and probably an inventory number. It's unlikely it's been plugged into 240V because a) it's located in the USA and 240V should be pretty scarce in those parts, and b) it has a 110V plug on it. I doubt it's suffered the fate you suspect. I have USA relatives; it could be mine.....
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Re: Retro SSTV Anyone? II

Postby Klaas Robers » Fri May 12, 2017 7:01 am

And it shows an extra switch on the front, as well as two extra indicator LEDs. One of them could be an SSTV sync detection LED, I mis that in the original circuit. It would be very usefull when tuning in on an SSTV signal.

I am happy that mine is almost not modified. Last weekend I got my old tone generator back, so I can now check the SSTV input chain and even the ADC. The input is rather sensitive, with no input signal at all it displays typical FM noise. I haven't seen that on the oscilloscope yet. Tomorrow I have quite some time.....

The Robot 400 has standard a two input winding mains transformer, Steve, see the sent circuit diagram. So it is easy to convert to 230 volt in, even if it comes from the US. I also see some non standard connectors on the back. It looks as if the video memory can be read and written through a muli-pin connector to and from a computer. This might be called the DMA (small extra switch on the front). Any way the unit is no more almost standard.

Ebay.com informs me that I can order it to The Netherlands. That will cost me $ 57.40 extra on shipping and transport. Strange that you can't get it in Thailand....
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