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BBC1 "World" generator aka C.O.W

 
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Re: BBC1 "World" generator aka C.O.W

Post by Michael Watterson » Mon Sep 16, 2013 10:24 pm

A pair of shorted adjacent pins on any one socket?

 
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Re: BBC1 "World" generator aka C.O.W

Post by Refugee » Mon Sep 16, 2013 10:51 pm

There was a bad batch of EPROM sockets out there what the unit was made. They even got into Tektronix scopes for a short while. I have forgotten what forum I read about them on. I had one on a VGA screen and due to time and what we would get for doing the repair I tied it in with a Tywrap.

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Mon Sep 16, 2013 11:52 pm

Hi Graham,
Yep tried the dip switches, thought this might be the cause as one of them was ever so slightly out of position, but after giving them all a good 10 or so operations and re setting the code .. No change.

Hi Refugee,
The Eprom sockets are all good quality gold plated turned pin variety (what else would you expect from the BBC) the sort that are specifically designed for multiple insertions (oh err missus!!)
Mind you I have come across the type you mean, nasty spring strip sort of thing where sometimes the spring bends up when the chip is pulled. Then there are those transistor sockets which TEKtronix seem to like. I have a wave form monitor "featuring" these which regularly needs a wiggling session.

And Hi Michael,
gave them all a good look over with the magnifying glass before they got pulled for the board swap. Having a leg "out the hole" was my first assumption too.

I'm tending to think something is going weird on the address buss, as the gold disc and perspective lines are one of the test patterns which is being read from another memory block. If you look at the frame grabs full size by clicking on them, you can just make out that the 2 images are interlaced. also when watching this live it was never the same each time. A couple of times when SEQ_7 was read it was almost normal with just a few random flickers then next time much worse or same as the frame grabs.

Oh well looks like I'm going to be doing some good old fashioned reverse engineering tracing tracks back from the roms to the address and data logic

off to bed now

regards all,

Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by Michael Watterson » Tue Sep 17, 2013 9:39 am

My theory is a 2bit map
The value thus selects Black, Gold or Blue or Grey. (maybe 00 = Black, 10 = Gold Globe image, 01 Blue Globe Image and 11= grey)

But I wasn't thinking of an EPROM pin, I was thinking of two adjacent socket pins shorting at reverse / track side of PCB. Even a shifted flake of solder etc. One short I think will do it.

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Wed Sep 18, 2013 12:27 am

Hi Graham,
I suspect you have much more understanding of the actual programming of the COW than me :)
I would say, having re read some of the other web articles, you have pretty much got the principles spot on in your description. Perhaps the words "test image" are a bad description, as in reality they are simply the foreground or background images, or mixtures of both selectable for test / line-up purposes
As you say, the foreground gold disc image is "breaking through" because the data to mask it is corrupt.
What threw me a bit is when a sequence card is out of its slot or some roms are out of that card with card in place, only the background blue disc and logo are displayed when that card / eprom are read.
However this makes sense when you realise that to "turn on" a particular pixel of the foreground gold disc and make it visible you require data bits from the roms whether its vaild or corrupt. No rom card or individual rom obviously means no data bits, so no foreground pixels are "turned on" to become visible over the blue background disc.
On the last sequence card there are only 12 map data roms and 6 roms prefixed TST. I wonder,Would these be responsible for the "quadrant" test pattern ("test pattern 3" in one of my frame grabs a few posts back) as its this last card that has its "read" led illuminated when that image is shown. Will try removing some of the roms to confirm when I have my next play.

Regards
Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Wed Sep 18, 2013 12:44 am

Hi Jeffrey,
No sadly I didn't get an extender board with mine either. Thanks for the offer of the use of a potentially suitable one though. Without one the only way to do active testing will be to put the card in position 10 in the card frame and try to get at things via the spare card spaces between it and the controller card ( which isn't much really)
Haven't had any time tonight to look at the card any further, maybe tomorrow

regards

Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Sat Sep 21, 2013 11:48 am

Hi All,
Last night I found the problem with the SEQ7 memory board - and looks like it was self inflicted :ccg

brokentrack.jpg


This tiny nick was enough to intermittently open circuit the A1 address line of the last row of eproms IC03 - IC73. A quick scrape of the track and a single strand from a bit of multicore flex soldered over the break has restored bovine contentment.

The backs of the circuit boards are screened with aluminium plates which also form an indexing key to prevent insertion in a wrong slot. These have nice square (if not particularly sharp) corners and I'm guessing one caught the board as I had several cards out at once piled up :aao whilst reading the eproms

I also had a quick play with the TST eproms on the last memory card (SEQ 9). With TST950 & 951 removed the gold disc foreground image is no longer available as a "test" image when selected by the rotary switch only the blue disc background image is displayed. From memory, I'm not on main pc now so can't check, I'm sure the eproms are filled with either FF or 00 as it made me look twice and have a couple of goes at reading them when backing up.
This ties in with the previous discussion about the sequence data keying bits of the foreground over the background, as a run of continuous identical data results in the WHOLE foreground image being displayed.

Regards
Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by Refugee » Sat Sep 21, 2013 1:21 pm

I was about to say that the damaged track was due to a bad tool being used to extract the EPROMs during copying. There is a lot of them and that increases the risk of concentration being lost.

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Sat Sep 21, 2013 6:15 pm

This is my extractor tool RS 489-2128

R4892128-08.jpg


I think it was my clumsy card handling that did it, there was also a de-coupling cap that got bent over pulling the leg out of the can so it was replaced.

bentcap.jpg


Regards
Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by Refugee » Sat Sep 21, 2013 6:23 pm

When I am working on racks I usually slide the cards most of the way back in but not engaged for safe keeping while I am working and then engage them again before powering up and testing.

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Mon Oct 07, 2013 7:10 pm

Hello All,
Been a bit busy last couple of weeks so the cow went on the back burner.
Over the weekend I got the horrible RIFA caps in the psu swapped for some decent class x and y as appropriate.

My thoughts have turned to fabricating a cover plate for the bottom memory card rack. Brushed aluminium plate is easy to come by, but I'm struggling to find the matching "card handle " strip a sample of which is shown below

Pict0193.jpg


Pict0194.jpg


I have tried the Rittall website but this profile of handle seems to have been discontinued. I wondered if anyone out there has a better knowledge of 80's sub rack case makers and can point me in the right direction ??

Regards
Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by Alistair D » Mon Apr 07, 2014 11:26 am

BVH2000 wrote:Hello All,
Been a bit busy last couple of weeks so the cow went on the back burner.
Over the weekend I got the horrible RIFA caps in the psu swapped for some decent class x and y as appropriate.

My thoughts have turned to fabricating a cover plate for the bottom memory card rack. Brushed aluminium plate is easy to come by, but I'm struggling to find the matching "card handle " strip a sample of which is shown below

Pict0193.jpg


Pict0194.jpg


I have tried the Rittall website but this profile of handle seems to have been discontinued. I wondered if anyone out there has a better knowledge of 80's sub rack case makers and can point me in the right direction ??

Regards
Neil


At work during the 80s and 90s we used quite lot of Vero racking. They did a separate catalogue for this.

Al

 
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Re: BBC1 "World" generator aka C.O.W

Post by Cathovisor » Mon Apr 07, 2014 5:52 pm

ppppenguin wrote:In the light of the smoke reported by BVH2000 and the smell I'm getting I really ought to check for iffy suppressor caps and mains filters.

I'd direct my attention to any soft-start circuitry first: IIRC the Advance MGT-series had a soft-start circuit and you could get quite a smokescreen out of these when the electrolytics in the soft-start circuit dried out.

The soft-start consists of a large wirewound resistor in series with the bridge rectifier on the mains side, and the theory is that after a short period determined by the electrolytic used in the timing circuit, it fired a triac that shorted out the wirewound. You don't need me to tell you what happens when it doesn't, but I had numerous occasions of this happening before we decided that it wasn't funny any more, we took all the PSUs out of service and replaced the electrolytics with 125 deg. C. ones and repaired/replaced the soft-start boards as appropriate.

The same PSU was used in the Designs Department digital decoder.

I'm sure I had some drawings for the MGT family PSUs... and you can still get them repaired if needs be:

http://www.advanceproductservices.co.uk/PSU-Repair-List.html
Last edited by Cathovisor on Mon Apr 07, 2014 6:05 pm, edited 2 times in total.

 
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Re: BBC1 "World" generator aka C.O.W

Post by Cathovisor » Mon Apr 07, 2014 6:03 pm

From my fading memory, it's internal. I'm pretty sure they had the soft-start, but I could easily be wrong and confusing it with another model.

 
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Re: BBC1 "World" generator aka C.O.W

Post by Cathovisor » Mon Apr 07, 2014 8:26 pm

Pretty sure I saw them in one of the stores, from when I cleared my locker out at work. It was literally cleared - I put it in my trailer and drove off with it! :bba

I've put feelers out with a former colleague and friend who used to build SMPSUs in a previous career - he may have kept the maps from when he left TC.

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Mon Apr 07, 2014 9:07 pm

Hi Jeff,
A quick reply to some of your questions
There is no sync on Y on my cow either and I have not found any obvious links etc to enable it. I assume station mixed sync was always readily available for pal coders and monitors so no need to combine it for its original use.

my PSU is PS4/11 and doesn't have the 2 screw heads visible on the front panel. It has the torrid pcb but the switch mode seems a different type, will try and get some pictures up soon

I'm surprised your mains lead is captive ,mine has XLR LNE on the back panel nicely marked MAINS .I guess the H&S police may have mandated the change if the cow has been in use post plug and socket regs. Incidentally mine was covered in "failed safety test stickers" quoting "able to insert fingers into case"

You are correct about a sequence memory card out of slot interrupting the animation. From your pic it looks like SEQ9 (the tenth card) which I think will also prevent the test image being displayed.
The sequence cards can be put in the rack in any order as the address is set on the card with dip switches so the above assumes the LEDs scroll in sequence from L to R when operating.
By the way, the cards are sometimes a right sod to get back in the edge con, quite a few times I have dithered about "giving it some" to get it to engage but they eventually go with a bit of wiggling and even pressure.

Now, what I would REALLY like to know, what region or nation do you get displayed under BBC1 when you operate the CEEFAX switch ????
Also out of interest what are the serial numbers of the memory cards, mine are /157 to /166 for the seq memory (except /298 where /160 would be) and /9 to /12 for the fixed memory the crate itself is /7

Glad you first light (moo?) was a bit less pyrotechnic than mine :-))

Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Mon Apr 07, 2014 9:24 pm

Hi again Jeff,
Just noticed something in your first pic, is that the front panel of the bottom section on top of the crate ??
If so, could I beg and bribe you for a scan of the artwork as I have sourced a new blank panel for my missing one and would love to see if I can get it screen printed like the original.
I'm still searching for some suitable alloy extrusion "handle strip" tho :-((

Kind regards

Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by Cathovisor » Mon Apr 07, 2014 10:09 pm

BVH2000 wrote:There is no sync on Y on my cow either and I have not found any obvious links etc to enable it. I assume station mixed sync was always readily available for pal coders and monitors so no need to combine it for its original use.

That'd be correct. The practice, in my workplace at least, was for unencoded signals to be distributed RGBS - YUV(+S) was quite a rarity. Syncs and Blanking were distributed pulses from CAR (along with VAS and CSC, and earlier - LD and FD) and were fed into the coders, so there was no need for any unencoded piece of kit to produce syncs on its output.

I suspect the reason the Museum's has been modified to a captive mains lead was simply to get rid of the (deprecated) XLR-LNE easily. Punching the panel to take a regular IEC inlet would seem to be a good idea.

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Mon Apr 07, 2014 10:45 pm

Cathovisor wrote:
BVH2000 wrote:There is no sync on Y on my cow either and I have not found any obvious links etc to enable it. I assume station mixed sync was always readily available for pal coders and monitors so no need to combine it for its original use.

That'd be correct. The practice, in my workplace at least, was for unencoded signals to be distributed RGBS - YUV(+S) was quite a rarity. Syncs and Blanking were distributed pulses from CAR (along with VAS and CSC, and earlier - LD and FD) and were fed into the coders, so there was no need for any unencoded piece of kit to produce syncs on its output.

I suspect the reason the Museum's has been modified to a captive mains lead was simply to get rid of the (deprecated) XLR-LNE easily. Punching the panel to take a regular IEC inlet would seem to be a good idea.


I got a nice ex BBC rack of AM4/536 VDAs the other week.
Each 6 o/p card is nicely labelled such as CB (colour Black ?) NET1 NET2 (Network 1 /2 ie. BBC1 BBC2) and TC which I guess was Timecode (or maybe Testcard ?)

Regards

Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by Michael Watterson » Tue Apr 08, 2014 11:24 am

I presume "5" is what USA calls Component, the RCA connectors for Ordinary or Progressive video from DVD and also analogue HD? (They don't seem to have used SCART or RGB in USA domestic gear).

I presume S-video as common on S-VHS and also known as Y/C is Y + sync and PAL or NTSC Chroma?

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Tue Apr 08, 2014 7:41 pm

ppppenguin wrote:A few more observations.

The PSU is a heavy module with 3 main parts inside. There is a big unit, with huge heatsink fins on the back which I think is the +5V PSU.It's an Advance MGT400, looks like this one: http://www.ebay.co.uk/itm/Advance-MGT40 ... 7675.l2557 though I'm pretty sure the one int he COW is doing a 5V output. Possibly a switchmode with a conventional 50Hz mains transformer. Then there's another packaged module with markings I don't fully understand. Marked NSR 512-9 LiPC. This would appear to be a switchmode -5V regualator: http://www.datasheetarchive.com/dl/Data ... 285489.pdf The final module is a PCB with a toroid (filter?) and a few other bits on it.


Some pictures of my power supplier PS4/11

6.JPG

1.JPG

2.JPG

7.JPG

4.JPG

5.JPG

3.JPG

11.JPG


Jeff looks like you PSU is a later equivalent model. Does yours have the 7905 -5v reg on the torrid board which has been replaced by your -5v switchmode module, or is the switchmode the original _5v reg for this model ?

Neil
Last edited by BVH2000 on Tue Apr 08, 2014 7:48 pm, edited 1 time in total.

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Tue Apr 08, 2014 7:46 pm

ppppenguin wrote:The Museum's COW has clearly been modified. The telltale mounting holes of an XLR-LNE are just visible.


Mains inlet on my crate

12.JPG

13.JPG


Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by Cathovisor » Tue Apr 08, 2014 8:13 pm

The whole thing would have been the PS4/11 - mounting frame, filter, 'commercial' power supplier, the lot.

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Tue Apr 08, 2014 8:36 pm

Cathovisor wrote:The whole thing would have been the PS4/11 - mounting frame, filter, 'commercial' power supplier, the lot.



Yep, Here is description on mine

PSU.jpg

ppppenguin wrote:The front panel of my power supplier is marked PS4/29. It looks like something has been scraped off and 29 put in its place.

Neil, does your power supplier make little buzzing and singing noises?


pretty much silent if I remember, give me a min and will go and hunt down a XLR LNE lead and check for you

Neil

 
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Re: BBC1 "World" generator aka C.O.W

Post by BVH2000 » Tue Apr 08, 2014 8:56 pm

Jeff,
The PSU is dead quiet with and without sync :aad

But I've got problems now :aai , Plugged it into the TV to have a little spin only to find the last 8 or so fields of the anim are corrupt in the same style as when I had an O/C address line on one of the other cards :bbd
This time its on SEQ9 card, spookily the one you were having difficulty getting into your card rack

I'm off to wiggle some eproms and check card seatings

neil

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