Marconi (Venner) TF 2423 500MHz divider

[factory]

There seems to be nothing on the web for the Marconi TF2423 divider that I can find, it's a rebranded Venner unit, I've not found the model number for the Venner version. The back lacks any serial number, no idea why.



It's about half the size of the Racal divider of similar spec, probably as it doesn't have a switched attenuator, the input board does however use the same Plessey SP630 divider IC, but without the tunnel diode for the input, there are couple of HP Schottky diodes.



The second divide by ten & output buffer board uses a 74196 decade counter IC and 747 dual op-amp.



Power supply is much simpler, there is a L036 +12V regulator IC on the chassis, there must be +5V for the TTL and a negative supply for the Plessey divider, I'll find out what this might be when I test it.



David

[factory]

Checking the voltages on the first power up, I had +11.9V on the output of the regulator IC, the others were very low at -2.4V and +1.3V, there was no signs of a dead short, nor any excess power consumption.

Removing the two boards to leave just the power supply, I got -12.2V and +5.29V, this meant the fault was with one the two divider boards. Plugging the second divider board in gave the same result, therefore the fault was narrowed down to the first divider/input board.

Checking the connections that go to the faulty rails I found the +5V rail was about 1.3k, with a 33uF 10V tantalum bead near the connector, removing this cleared the fault, it doesn't measure shorted after removal. I've fitted a 33uF 16V electrolytic as that is all I have in stock.
There should be a approx -5V somewhere on this board too, as the datasheet for the SP8630 divider uses this, I've not found a datasheet for the SP630, but the Racal circuit with the same part uses -5.4V.

PSU output voltages are now as follows, connections from left to right in picture;
Black/red wire, orange links = 11.94V
Light grey links = -12.16V
Red links = +5.26V
2x yellow wires, unreg AC
Black/orange wire, unreg DC to +12V regulator.
Black wire ?
Black/brown wire, darker grey links, case ground.



The unit is now mostly functional, here it is connected up to a suitable low frequency counter and measuring/dividing 399MHz to 3999kHz (the counter is rated for 2.5MHz max). The input valid function appears to be dead, someone has changed the lamp for an LED in the past.



David