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Ex BBC Scotland PM5544 Colour Pattern Generator Restoration

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colourmaster
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Ex BBC Scotland Philips PM5544
Colour Pattern Generator Restoration

The Ex BBC Scotland PM 5544 Colour Pattern Generator arrived in a poor state, with side covers missing and the top covers held in place with Duck tape with tales of the various faults the unit had exhibited and that the unit was burnt out. The covers were removed and an inspection of the unit made. Each board was removed and visually inspected and the power supply electrolytic capacitors and PCB (Printed Circuit Board) decoupling capacitors tested for leakage, value and ESR (Effective Series Resistance). In total nine of the electrolytic decoupling capacitors were found to be of low capacity and high ESR and these were all replaced modern low ESR 105 degree C capacitors of the correct value.

The PCB’s were then replaced and voltmeters attached to the various supply rails from the power supply. Power was supplied to the unit by means of a “Variac” (A variable output mains transformer) and the readings on the power supply voltmeters observed. All the power supply voltages were with specification and no excessive currents measured.

In order to go further into the testing of the unit a PCB board extender was made to enable tests to be made on the PCB’s. It was also necessary to connect the PM 5544 to the correct signals as obtained from the PM 5532 Sync generator and the PM 5545 Colour encoder units. After connecting the units up and terminating the signals to 75-ohm loads and connecting a small monitor to one of the four video outputs, the mains supply was switched on and a white raster was displayed on the monitor. Checks with an oscilloscope found that sync pulses were going into the Sync regenerator PCB (Unit 16) but nothing was coming out.

The board was removed from the board extender and DC checks made on the transistors in he Sync regenerator, and transistor TS2 a 2N2369A transistor found to be faulty. This is a very special type of UHF switching transistor which was not available, so not to be beat a 2N3904 was press into service and when the board was replaced Sync pulses were available on the back plane of the PM5544, although a little distorted, more about this later. The monitor was now displaying alternate horizontal black and white bars.

More scope tests on the Cross Gate PCB revealed that the 630kHz clock signal was going in, but there were no outputs from either of the two Horizontal dividers 1 & 2 and the signals from the clock buffer amplifiers, IC 11 a 7400 TTL IC (Integrated Circuit) Quad dual input NAND gate were low and distorted on horizontal divider No.2. Further checks on the horizontal divider IC’s 7474 TTL IC D type dividers IC’s 1 to 10 revealed three faulty dividers in IC No.1, 2 and 6, the three IC were replaced and the unit tested. The monitor was now displaying black and white horizontal bars with a floating cross hatch in the black bars. Further tests with the scope revealed that horizontal divider No.2 was working and producing the correct signals at the outputs, however divider No.1 was still not dividing and the clock pulse from the buffer in IC 11 was even more distorted. IC 11 7400 was replaced with a new chip, as when tested out of circuit was marginal on its outputs pins 3 and 6, which drove the clock for divider No.1.

On replacing the board, the monitor displayed a crosshatch pattern with castellations along the top, bottom and left hand side and the colour matrixing signal only on the left hand side and the bars were at the wrong position on the screen, approximately one clock pulse too early.

Further checks were made on the Cross Gate PCB with a four channel digital storage scope triggered from the master clock. All the signals on the horizontal dividers were checked for timing and the only anomaly that was found was on pin 8 of IC No.2 7474, this pin produces signal H5-25 which is the complement of the signal on pin 9. A clear ghost signal could be seen in the background of the correct signal. The solder joints around the IC were re-soldered, the board retested, and the monitor displayed the correct test card with BBC 2 in the lower black box, checks with the scope revealed normal signals on the horizontal dividers. However this was not to last after a short time the picture twitched and went back to cross hatch pattern and touching the board any ware with a scope probe would make the test card come and go.

The board was removed and IC No.2 was removed to check the continuity of the PCB tracks on both sides of the board and the plated through holes. Testing between the tracks and the IC solder pads revealed a 30 ohm resistance between the unused pin 8 and a thin 0.5 mm track passing between the pads for pin 8 and 9 of the IC. This thin 0.5mm track was the clock pulse for divider No.1. The print on the top of the board had been tinned and the connections from the bottom of the board and the top were via plated through holes and solder was applied to the bottom of the board. No reason for the 30-ohm test between the pad on pin 8 and the clock line could be found, other than perhaps a tin whisker.

The gaps between the print and the pads were cleaned with a scalpel but there was still 30 ohms between the pad and the clock track. As there was no visual evidence of a tin whisker all the pads and tracks in the area were tinned with normal 60/40 solder and the surplus solder removed with a vacuum de-soldering tool and the continuity tests revealed that the 30 ohm leak between the clock track and pin 8 pad had gone. IC No. 2, 7474 was then replaced and a normal test card was displayed with the raster phased slightly to the right.

The correct Sync type of transistor (2N2369) had been ordered and samples were tested for a gain of 40 and one selected and fitted to the Sync board to replace the 2N3904 transistor. On testing the monitor displayed a correctly phased raster so no adjustments were necessary to the Sync board.
The next PCB to check was the Definition Lines; this was checked with the storage scope and the frequency of the definition line checked and adjusted and all found to be within tolerance.

On checking the Teletext PCB it was found that BBC 2 was displayed in the lower black box but BBC 0 was displayed in the upper box, removing a link on the multiplex IC’s displayed BBC 1 but BBC 3 in the lower box. The PCB was removed and continuity checks around the 16 line Multiplexes and a short circuit was found between two PCB tracks decoding the 1 and 2 ROM address lines. With the solder bridge between the two tracks removed the correct numbers were decoded from the multiplexes.

Are there any ex BBC engineers out there who could help with information on the BBC modifications to the generator?

Regards
Gary

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Topic starter Posted : 18/03/2014 10:04 pm
ntscuser
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That's a very smart-looking monitor you've got there Gary, what type is it?

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Posted : 18/03/2014 11:18 pm
colourmaster
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Hi
the monitor is a 10" jvc professional type . A chap on ebay had a batch of them for £4 each , so i bought two of them . As for the restoration it was Stan (Electrical) who did the work with his vast knowledge of ttl technology . Also a chap called marc from Belgium who sent me the manuals .
i have two other original working pm5544 generators which i obtained from Belgium .
i would like to modify one of them to the BBC standard but i can"t seem to find any information .
i have been told that the BBC always give their modified equipment a four digit number . I have looked at the ex BBC Scotland version but can"t find any .
do any of you know how i could obtain the information ? .
regards .
Gary.

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Topic starter Posted : 19/03/2014 8:53 am
Focus Diode
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Excellent stuff indeed. Warmest congratulaions to Stan and yourself for getting it working. I remember seeing this pattern txd by BBC2 in the 1990s with the "BBC2" id at the top.
Would be wonderful to see how it looks on an old set.
Cheers,
Brian

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Posted : 19/03/2014 12:53 pm
Brian Cuff
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I echo the other Brian's comments. Not an easy job to get going but a very good description of a very logical fault-finding exercise on a complicated bit of kit. Excellent work, guys.

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Posted : 19/03/2014 1:16 pm
Cathovisor
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Hi
the monitor is a 10" jvc professional type .

Looks like a TM-1010 to me - used to use loads of them and the £4 price doesn't surprise me these days (they certainly weren't that when I bought new ones!). I can't remember if the 1010 suffered from the same fault as the less sophisticated TM-A10E, but there is an electrolytic cap positioned next to a heatsink that causes field cramping as it dries out.

I was remarking to an acquaintance the other day that I wished I'd grabbed hold of one of the 14" Sony monitors being chucked out from my old workplace that, in addition to RGB/YUV and composite feeds, also had an SDI input.

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Posted : 19/03/2014 1:42 pm
Refugee
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It looks like a serious challenge you have got there.
Well done getting first light.
Those monitors come up in big batches as media centers convert to wide screen at various venues.
I went to get a couple of 9 inch mono monitors as repeater screens for my CCTV and ended up with a car load including a 14 inch Sony and a 20 inch Sony. They were free :thumb

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Posted : 19/03/2014 2:19 pm
Cathovisor
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Those monitors come up in big batches as media centers convert to wide screen at various venues.
I went to get a couple of 9 inch mono monitors as repeater screens for my CCTV and ended up with a car load including a 14 inch Sony and a 20 inch Sony. They were free :thumb

A lot of these monitors do widescreen switchable (along with underscan) anyway - the TM-1010 mentioned earlier does, as did the Sony I mentioned earlier; but I'm not surprised at the disposal methods - the last I heard was that one company was charging £9 a monitor to dispose of it according to WEEE regulations. 'Glass' is worthless now except in one or two specific aspects, such as monitoring for lip-sync and camera/lighting control - and OLED monitors, with their 'true black' capability, are rapidly taking over there.

Far easier - and more cost-effective - to stick 'em in a pile and say "take what you want".

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Posted : 19/03/2014 3:02 pm
Cathovisor
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i have been told that the BBC always give their modified equipment a four digit number . I have looked at the ex BBC Scotland version but can"t find any .
do any of you know how i could obtain the information ? .
regards .
Gary.

Do you mean the Coded Equipment Number? (e.g. EP5/512, AM4/536, LS5/8, that kind of thing?) I have a friend who used to work in CAR at Television Centre: once upon a time they had PM5544s but they may well have been ditched after the fully-electronic generators for Testcards F, J and W were introduced. The paperwork might have survived though, but I expect the exodus from TC led to a lot getting binned. I'll ask.

The danger is that it could have been a local mod. and thus never properly documented.

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Posted : 19/03/2014 3:07 pm
Refugee
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The two colour Sony monitors I have are not wide screen with a DVD player plugged in.
I don't think there is any chance some how as there is nothing in the hand book I downloaded.

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Posted : 19/03/2014 4:28 pm
Brian Cuff
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Blimey! Those were the prices for BVWs and the like. Now, just a 25" monitor.
IIRC, the original Sony 20" HD grade 1 monitors were also approaching that price when loaded with all the input cards. Propper TV broadcasting is (was) a very expensive business. I can remember the colourisation of TV Centre studio 3 costing £500,000 for just the video installation and that was in 1966(ish).

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Posted : 19/03/2014 8:05 pm
Electrical
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The BBC version of the PM5544 has the ferrite core memory fitted for the circle generator, other versions are fitted with an EPROM, and there are at least three different versions and revision levels of the hardware fitted in these generators.

The BBC version is also modified to provide six frequency gratings instead of five and the horizontal timing signals are modified to start earlier than the basic PM5544. The frequencies are also different from the standard. There are lots, of piggy, back TTL chips mounted on top of other chips and in between chips to provide these functions.
I have a PDF copy of the EPROM version and I can put it in the Library with the PM 5545 PAL Encoder and the PM5532 Sync Generator if you wish.

With reference to the 2N2369A transistor, it is a 500MHz, switching transistor with a gain {hfe} of 20 to 40 and I have not found anything suitable to replace it, as most equivalent transistors have too high a gain. The sync transistor was replace with various type and all caused problems with the shape of the waveform and hence the timing. The correct 2N2369A selected for a gain of 40 cured all the problems without any adjustments.
Regards Stan.

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Posted : 19/03/2014 8:08 pm
Refugee
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The monitors I have are the 5E ones that do not have the RGB on BNC plugs but all the same they have both found homes around the house.

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Posted : 19/03/2014 8:12 pm
Refugee
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Would there be any value in looking for transistors that are sold as switching types?

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Posted : 20/03/2014 12:39 am
Cathovisor
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Blimey! Those were the prices for BVWs and the like. Now, just a 25" monitor.
IIRC, the original Sony 20" HD grade 1 monitors were also approaching that price when loaded with all the input cards. Propper TV broadcasting is (was) a very expensive business. I can remember the colourisation of TV Centre studio 3 costing £500,000 for just the video installation and that was in 1966(ish).

That seems quite a high price, but it is a 'Grade 1' - this is more like it for a general preview monitor:
http://cvp.com/index.php?t=product/sony_pvm-a250_monitor

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Posted : 20/03/2014 2:46 am
Electrical
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The PDF copies of the manuals for the Philips PM5532 “Colour TV Sync Generator”, PM5544 “Colour Pattern Generator” and PM5545 “PAL Colour Encoder” are now in the Library, in the Test Instrument section. (18Mb)
Please note that the manuals are for the later versions of the generators and are different from the BBC early version. The Sync panel in the PM5544 manual is a half size board, in the BBC version it is a full size card and circuitry is different. The circle memory is an EPROM card in the manual and a ferrite core memory with an extra card in the BBC version. The frequency, grating card is also different and has been modified along with the back plain signal lines and switching. In addition, the Teletext card and current gate are different from the manual version; the character generator logic does not seem to follow the ROM contents.
If anyone has any details of the modifications done the BBC version, I would be very interested, especially in the correct procedure to set the inserted text.
Also note nearly all the components are 1%.
Regards Stan.

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Posted : 20/03/2014 11:09 am
colourmaster
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Hi
here is a picture of my pm5544 which is the original version .
you will notice the differences between this and the bbc version .
does anyone have any information of the modifications to the definition lines board ? .
i have looked on the BBCengineering equipment list but can't find anything on the pm5544 .
i would be grateful on any help .
regards .gary.

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Topic starter Posted : 28/03/2014 1:08 am
Brian Cuff
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Normal professional design practice to use 1% or perhaps 2% metal film resistors such as Mullard MR25 series for all low power applications. Certainly as far back as 1980 and probably further back .

During the discrete solid state era, say 1962 onwards, all BBC coded equipment used the Erie ceramic tube 2% hi-stab resistors almost exclusively. The 1/8W versions were very useful for home projects and Central Stores only stocked this one type, from 2W to the tiddlers so what else could we use? :qq1

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Posted : 28/03/2014 2:36 am
Brian Cuff
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Actually, the quarter watt versions are the same size as the non-HiStab half watt. The eighth watt are the same length but only about 5/32" in diameter. I suppose that, in comparison with today's components, they are quite large but in my opinion, look fantastic!

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Posted : 28/03/2014 11:28 am
Anonymous
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The BBC version of the PM5544 has the ferrite core memory fitted for the circle generator, other versions are fitted with an EPROM, and there are at least three different versions and revision levels of the hardware fitted in these generators.
The BBC version is also modified to provide six frequency gratings instead of five and the horizontal timing signals are modified to start earlier than the basic PM5544. The frequencies are also different from the standard. There are lots, of piggy, back TTL chips mounted on top of other chips and in between chips to provide these functions.

I have a PM5544 that used to belong to the Australian Broadcasting Commission. It has the ferrite core memory and the standard five frequency gratings. It has an additional card, which did not appear to be made by Philips that replaced the patterns inside the circle with a blue field and yellow text saying "Please stand by" when the 'ext pict' button was pressed.

It also contained the text insertion card (labelled as from a PM5543) which was programmed to display "A.B.C" in the top rectangle and "CAIRNS" in the bottom rectangle. It probably explains why the power supply was completely cooked! (Cairns is located in far north Queensand and has a hot climate). It was quite a while ago, but I vaguely remember completely reworking the power regulator circuits, removing a small card that contained some of the power supply circuits in the process.

As I did not have the appropriate sync generator and PAL encoder, I made my own, on a small card that plugged into the vacant and rewired slot that was originally occupied by the regulator card, making my PM5544 self-contained.

I don't know how old my PM5544 is, or what version it is, I should open it up again and see if there is anything that might provide a date inside.

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Posted : 12/03/2015 4:37 pm
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