16-02-2017, 07:35 PM
Well, every other voltage is slaved to the -15V line, which in an earlier mail you reported to be -14.66V (which is out of spec). If you adjust that to be -15V, all the other lines will come up much closer to the specified voltages. As a ratio the -69.7V will come up to about 71.5V, about 4.5% low. Which is now*slightly* out of tolerance.
And from what I can see it is only used in two locations on the storage board into high impedance points. Which will be supremely indifferent to the -75V being a tad out of spec.
Your problem is not with the power supply! It is a red herring. You need to dig elsewhere, almost certainly on the CRT circuit diagram 11, not the storage circuit diagram 12.
There might be a proviso to that statement about the supply though:
You are right to check the HT. -4.1kV comes onto that board from a voltage adder circuit *on the power supply* (Ha!). Which means that you need to be careful poking around, because getting your finger on several kV DC is likely to spoil your day. You will need a 1000x high impedance probe to test that. There some highly stressed capacitors in there which can break down with the passage of years under sustained high voltage - particularly C990 and C934, 10nF 5kV. These are high-K (Y5S), wide tolerance ceramic caps (+80%, -30%). Check with a magnifying glass for damage to those - areas of blackening, pieces of the encapsulation that have broken away, cracks etc.
And if you are testing around that circuit, use the high voltage engineer's trick - keep one hand in your pocket. A jolt from one hand to ground is less lethal than one that goes from one hand to the other via your heart.
Are we having fun yet?
And from what I can see it is only used in two locations on the storage board into high impedance points. Which will be supremely indifferent to the -75V being a tad out of spec.
Your problem is not with the power supply! It is a red herring. You need to dig elsewhere, almost certainly on the CRT circuit diagram 11, not the storage circuit diagram 12.
There might be a proviso to that statement about the supply though:
You are right to check the HT. -4.1kV comes onto that board from a voltage adder circuit *on the power supply* (Ha!). Which means that you need to be careful poking around, because getting your finger on several kV DC is likely to spoil your day. You will need a 1000x high impedance probe to test that. There some highly stressed capacitors in there which can break down with the passage of years under sustained high voltage - particularly C990 and C934, 10nF 5kV. These are high-K (Y5S), wide tolerance ceramic caps (+80%, -30%). Check with a magnifying glass for damage to those - areas of blackening, pieces of the encapsulation that have broken away, cracks etc.
And if you are testing around that circuit, use the high voltage engineer's trick - keep one hand in your pocket. A jolt from one hand to ground is less lethal than one that goes from one hand to the other via your heart.
Are we having fun yet?
