Telequipment D43 Help!

[notallbad]

Yes Hi Ron

The long green thingy with 5 nut and bolt lugs.

I take it that this is like an array resistor, so its R412, R413, R414 and R415 all in one package.

So from left to right I get around 1kohm between each pair of lugs except for the last 2 lugs (O.C). Oops, that looking at the resistor from the rear of the unit.

[ronbryan]

Well done. The 40W power resistor is constructed as a centre fed 4k resistor, tapped at 1k intervals as far as I can see.

You should be able to see if the cap is s/c without removing it, by testing from the o/c resistor lug. Test with and without the plug-ins inserted if you get a low reading.

The lack of focus on the upper trace may be due to an o/c resistor in the focus divider chain.

You should be able to do a cold check (scope off and disconnected from the mains) on the 1.8M and 820k resistors which are fitted to the focus pot as shown in my photo. The focus pot is the one nearest the front panel. If these are ok, check the pot.

These resistors are fed from the -1kV supply, so be aware of this danger. If you find them faulty, you need to use resistors rated for at least 500V or higher. I use the Vishay VR37 type.

Ron

[notallbad]

Would appear both resistors are O.C.

So would I be able to use a 10W 1kOhm, I take it 40W is the overall power rating?

[notallbad]

The power resistor measures 1kOhm between lug1 to lug2, 2kOhm between lug1 and lug3, 3kOhm between lug1 and lug4 and O.C between lug1 and lug5.
Also 1kOhm between each paired, lug1-2, lug2-3, lug3-4, O.C - lug4-5.

Just to clarify.

[ronbryan]

Yes, 1k ohm 10W would be ok.

Did post #26 refer to the focus resistors 1.8M and 820k?

Ron

[notallbad]

Thats correct

[notallbad]

Thankyou for your help Ron,

So just to update:
Fitted an Axial 10W 1kOhm wirewound resistor obtained from Maplins across the two lugs on the O.C part of the power resistor.

Powered up and hey presto! Its working, all except Focus due to O.C resistors, will hopefully get that sorted out later this week.

I did in fact check the caps too earlier just to be on the safe side, namely the 450v 100uF that 'feeds' directly off the blown power resistor circuit. It was reading 2kOhms, so not S/C, the 2kOhm due to it measuring across 2 of the 1k res on the power resistor, if the cap had been shorted the reading would have been lower and I take it resistance on a cap this size should be high if not infinite.

I almost feel like digging out my S51B that is well and truly buried in the shed, I do remember a fuse blew in it for some reason, not really sure why and didn't have any suitable replacements, 32mm .5A anti-surge fuse, may have to change the fuse holder to fit a more widely available 20mm glass fuse.

[Tim]

I ran a D43 for many years and the source/cause of most of the faults(including focus/y shift problems as I recall) were those horrid black carbon resistors. The service manual is quite good , with comprehensive circuit diagrams. Any faults will usually be indicated by erroneous voltage readings.

[notallbad]

Thanks Tim shall keep that in mind for future reference.

Speaking of the manual, yes I thought it pretty good and well documented however I appear to have a different version Power board PCB, its referenced as PC3 in the hardcopy manual that I have and PC3A on the manual link referenced earlier in this thread, whereas I have Version PC4B which was somewhat confusing until I realised shortly after starting to troubleshooting. There are some slight differences and certainly much better than no schematic at all!

[notallbad]

Pot resistors replaced, 1.8MOhm and 820kOhm, and FOCUS now working.

Thanks again!