Hi BTO,
Your piece of candy is a capacitor.
I use to have a sheet with the color code, but at the moment it seems to be out for beans
John.
HOLD THE PHONE.... We have a problem
While looking around at the Transformer, i noticed this....
There is cap that , for some reason, is not connected to it's solder joint (could it be that easy ?)
Let's find out
Does anyone know how to check if i have power going into the C.R.T.
Does anyone know how to check if i have power going into the C.R.T.
Do you have a HV DC meter? Like a BK precision HV-44? Or something similar that can safely measure voltages above 20kV DC? If so, proccess is simple for checking anode voltage. Disconnect anode cap or plug, and use the meter to measure the voltage from the anode voltage source.
Also check the pre-acceleration voltage. Should be around 500v to 1kV??? I don't have the service manual for this thing, and I can't find it in the link you provided.
The simplest step would likely be to check the filament voltage. Check the two filament wires and check for a voltage of 6.3v DC or AC RMS. Then check the resistance of the heater element. If it is open, the tube is garbage.
If a trace appears when it's switched off (as mentioned in the first post), the CRT is unlikely to be dead.
Seems to use mains derived HT, with some large capacitors in the multiplier stage, be very careful here.
The stick rectifiers are almost certainly selenium, these use a pile of selenium diodes in series in each tube, the voltage drop will be much higher than your DMM can test.
David
"The simplest step would likely be to check the filament voltage. Check the two filament wires and check for a voltage of 6.3v DC or AC RMS. Then check the resistance of the heater element. If it is open, the tube is garbage."
sounds pretty simple, How do i identify the 2 filament wires ?
I have the same model of oscilloscope. They're pretty reliable, but there are some things that go wrong.
Schematic: go to Kevin Chant's website, and look under test equipment, BWD.
The EHT supplies are mains-derived. The rectifiers go bad. Replace them with generic microwave oven diodes. I used 1N4007s in series, but that's not the best way to do it.
The BF197 and BF336 output transistors in the vertical amplifiers often fail, causing the trace to go off-screen. Equivalents in TO-92 or TO-18 cases are easily available (may even be BC108) - search datasheetcatalog for the datasheet.
And I had the uA733 (a 10-pin metal case IC) fail on mine, but fortunately at work we have lots of vintage semiconductors.
Rob
If you are going to connect rectifier diodes in series, you need to include high-voltage-rated bleeder resistors across them to make the reverse voltage drops equal. The example is R201-R204 across the capacitors C201-C204 in the CRT cathode bias supply.
It's less trouble to use microwave oven diodes. If you're in Sydney, go to WES in Summer Hill.
The circuits are here; https://www.kevinchant.com/uploads/7/1/0/8/7108231/506.pdf
Details of the CRT here; https://frank.pocnet.net/sheets/011/d/D13-27GH.pdf
BF197 is one of those lockfit transistors, lockfit transistors seem to have bad reputation.
David