Tackling the BRC3000 Series
By Steve Pendlebury

19" Ferguson CTV (BRC 3000 Chassis)

Despite the rumours and tales that follow the 3000 series around, they can perform very well and, well restored and maintained, can give good service and results. The Power Supply arrangement is the first Chopper Power Supply to appear in any TV set and this gives the set a lot of historical significance. The service tips and fault lists above have been prepared from my own notes as well as from BRC bulletins from the period which I had to hand when I was restoring my 3000 series sets. It is obviously not possible to list every single fault ever encountered in a set, so I have tried to list the more common or confusing fault conditions.

The Power Supply.

When the set is switched on, there is about a second’s delay before the set comes to life. This is normal. Any longer delay will be due to either a fault on the power supply or in the line output stage. This is usually followed by a rather more graphic display of where the fault lies. Another common occurrence is the operation of the overcurrent trip button on the back of the set.

If the trip or mains fuse blows at switch on, check the HT or LT rectifier diodes for short circuits. If you really are unlucky then there could be a short on the Mains Transformer. If Resistor R609 (15k) is overheating before the trip button blows, check the mica washer on the chopper transistor first as these can break down with age. If this is OK then the Chopper could be short circuit, also check diodes W606, W609 and W616. There is a crowbar, W621, that also fails. In order to stop the 60v rail from getting to be too high, there is a 72V Zener Diode W617. This can also be caused to strike when feedback amp VT608 goes faulty. If the trip button operates intermittently, check for dry joints on the Chopper Transistor VT604.

If the set sits there, no fuses blow and no trips fail, look first to see if the CRT heaters are alight. This supply comes straight from the Mains Transformer. If the tube heaters are lit, check next for the presence of the 30v supply from the Power Supply Unit. You can measure this on Fuse F602 on the PSU. If its missing, check back from the fuse to the mains transformer. VT601 is a 30v stabiliser, which can go open circuit. Another occasional offender is Zener Diode W605. If F602 is blown, look at W620 for a short circuit.

There should be full HT applied to the chopper transistor VT604. If not, check for DC on the Cathode of W602, then make your way forward to the chopper transistor.

The most common problem is no 60v rail. Look first at fuse F603. If this is blown, the chances are a replacement will blow again. The Frame and Sound stages can be isolated from the equation by operating the ‘set white’ switch on the video panel. Disconnecting tag A on the Line Timebase Panel can isolate the Line Output stage. One favourite cause of trouble here is the A1 smoothing capacitor C523.

If there is no 60v leaving the Chopper Transistor, check for a negative voltage on the cathode of diode W608. This should be about -15v if you’re using a proper AVO. (You are, aren’t you…!?) If you have the luxury of an oscilloscope, you can check the drive waveform on the base of the chopper and work your way back to the Line Oscillator module.

There should be 12v on both sides of the primary of the Chopper transformer (check here for dry joints) and the collector of VT605. If the voltage here is high, this suggests that the transistor is either open circuit or biased off. Check W610, VT606 and VT603. If this voltage is low and there is an overheating 100-Ohm resistor (R607) then check VT602, W607 and VT603 for open circuit. If the forward resistance of diode W607 is too high (over 2M) then the chopper drive will not operate.

Sometimes the 60v rail stays low, resulting in lack of width and frame foldover. There may also be evidence of a 50Hz ripple on the supply. There is a dynamic trip circuit in the power supply and this is set up with pot. R622. This pot can go open circuit and another thing to look at is W622. Sometimes this can read OK but still actually cause a problem. The SET EHT control can also be troublesome, as can the 1-Ohm resistor R610 and capacitor C614.

The Power Supply can also cause a few other symptoms that are worth a mention. For distorted verticals on screen, check C619 and C631.  If the brightness and width is varying, check for fluctuations on the 30v rail and change VT601. Occasionally there is no signal because of lack of LT supply to the tuner as VT609 goes open circuit.

Finally, there’s a 240v rail to the video board and this can fail if we lose fusible resistor R602 or occasionally diode W601.

The Line Timebase Panel.

Adjacent to the Power Supply panel is the Line Timebase Panel. If there is no 60v rail and the fault is traced back to the Line Timebase Panel, common offenders are C511 or C512, VT501, VT502, or more often simply bad or broken connections on L501.

There are two types of line output stage, using one or two line output transistors. These are easily identifiable as it/they are located on the upper side of the Line Panel.

In the event of No EHT and the 60v rail being present on R518, check the DC voltages on either end of (and indeed the condition of) R518. If there is no voltage drop across this resistor, check VT503 for open circuit and also T502 Primary and T501 secondary windings for being open circuit/dry jointed. If R518 has a high voltage drop across it, is overheating of has failed, then VT503 could well be short circuit. There is also a capacitor, C531, on the print side, which can go short circuit. If VT503 keeps failing, it is likely that there are shorted turns on the Line Driver Transformer T502.

If the Line Output Transistor(s) themselves go open circuit, it is a good move to check C517-C520 and W504 before replacing these transistors and switching on. These can cause excessive EHT and width problems, excessive brightness and loss of colour (no ident to decoder) .A curious condition is when the colour only reappears when the Horizontal Hold control is offset, this is down to C520 going open circuit.

C506 can cause severe vertical ringing or incorrect line frequency. The latter fault is also sometimes causes by C511.  When the line speed sets up Ok when the sync test point is earthed but will not lock when the short is removed, check C502.  Also striations on the Left of the picture result if R521 goes open circuit.

Tripler and Focussing.

The Tripler can hold a charge, just like the CRT can, so when fitting and removing this component, handle with care, It can cause fuse blowing and all the other problems you would expect a tripler to cause. The correct tripler must be fitted to maintain the correct focus volts. The focus control is a slider on the top right of the set, on the outside. This slider is prone to arcing and needs to be kept clean and free from dry joints and excessive dust. If this control seems to be at the end of its travel, look at R575 and R576. There is a focus spark gap on the tube base. This, along with the other spark gaps, must be kept clean to prevent spurious arcing.

Interesting Quickies From Elsewhere in the Set.

Most problems on the BRC3000 series seem to be confined to the stages mentioned above, but here is a list of ‘quickies’ relating to other parts of the set.

There are a number of thin brown ‘coil’ modules on the tube base and the video panel. If one colour is lost,. Check these as they tend to go open circuit.

Video Board:

Incorrect Background Colouring: C231, C227 and C215.
No Luminance: L201, VT201 cut off, 4.4Mhz trap open circuit.
Smearing: L205 o/c, C221, VT204.

Decoder:

Intermittent Colour: Check Crystal, also setting of R354.
Picture goes blue when colour control advanced:  Check C337.

IF Unit:

Blank Raster, Weak Sound: C179 s/c, C130 leaky.
Low Sound with buzz: C158, C159 in discriminator can o/c.
No Colour: Check VT110.

Frame Timebase:

Foldover at the top: C429.
Foldover at the bottom: VT424, C432.
Intermittent Frame Collapse or poor sync: VT421 VT422 faulty or dry jointed.

Sound Problems:

Low and Distorted Audio: C401 Leaky.
Buzz on Sound: Check frame transistor mounting bolts are properly earthed. Check C431.

Footonote.

I have seen more than one 3000 which has been fitted with a cooling fan over the top of the power supply. This must of course be done safely and I cannot comment as to how this affects or improves the reliability of the set. Perhaps someone can help me on this one?

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