Wells Gardener 19V1001

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obcd

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With a piece of wire, connect the base of Q209 to ground (or to it's emitter which is connected to ground). This will turn of the horizontal drive.

Load the 75V with a 25W light bulb.

Make sure you have the right transistor as shorting the wrong stuff might result in magic smoke.

Like that, you can run the chassis without tube connected. (Just make sure the neck board is on an isolated surface so that no shorts can happen on there.) Also make sure the anode cap isn't touching anything.

Fix the voltage regulating circuit so that the B+ is adjustable again and set it to 75V

Check the B+ voltage again afterwards, when the monitor is operational again.

A short on Q101 or Q102 could cause the voltage regulating circuit to behave like it does

A non functional Q204 (open circuit) can cause such behavour as well.

A broken ZD201 can also cause such behavour. The zener has a voltage marking and you should measure exactly that voltage over it. (That's why I asked)

A short or leakage of C206 can also cause this problem (the zener voltage will be 2 low)

The zener voltage is 31V.
 
Ronnie Dent

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Just one thing? as I'm hooking the chassis up to 240 mains on the bench I will set the jumper on the transformer to 220v feed, does it matter which way round I feed live and neutral? from the socket on the chassis one feed goes straight to transformer the other goes through a fuse first? am I right in thinking live will go through the fuse?

Thanks Ronne
 
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live and neutral doesn't matter. Just double check that the chassis is isolated from it's supply. (Some chassis can't work without an isolation transformer.) Since yours is having a transformer on the chassis, it should be fine. If there is an overcurrent, the fuse will blow, no matter if it's in the live or in neutral. If it blows, it will stop the current flow. (But it shouldn't) As the 25W lamp will only be feeded with 75 - 100V, it will consume approx. 8 - 10W. This should be enough as load.
 
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Right I think it went well? never had a 25w bulb so used a 15w? the lamp lit but the B+ now reads 114vdc? across ZD201 I read 33.65vdc? not looked at C206 yet but it would have been replaced.

Thanks Ronnie
 
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good luck.

if you have any doubt about what you are doing, don't do it.

you can also remove Q209 from the board to disable the horizontal output stage.

The problem is somewhere in the power supply circuit on page 3 of the manual.
 
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Sorry, missed your previous post.

Looks like your problem is not the zener.

What voltage are you measuring on the base of Q 101?

R103 is 180E

so, if you have a 5W load that would mean a current of 43 mAmps

Such a current should give a voltage drop on R103 of 0.043 * 180 = 7,9V

It looks like you will need a bigger load. I would try a 60W bulb.

This would give a maximum current of 250 mA and a maximum voltage drop of 45V (over R103)

The dissipation in the resistor would be 45 * 0.25 = 11,25W

It's a 10W resistor, so basically it's at it's limit.

But, since the load voltage will lower, so will the current.

Assuming that without load, you would have 114 + 8 = 122V

Q101 can only increase the output voltage. Without it, you should have an output voltage below 75V, or you will never be able to adjust it to that.
 
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Now hooked up 60w bulb B+ is 109v, ZD201 33v, Q101base reads 110v. is R103 the large wirewound resistor on the chassis? I think it is! if so with my leads across it I'm getting -1,5513v ?

I have ordered some MPSA06 transistors and 2N3773 to replace Q101, hope that is compatible? and hope the above tells us something

Thanks Ronnie
 
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Yes, R103 is a 10W resistor, so it should be large.

Maybe you could remove Q102 from the pcb. Doing so would stop driving the base of Q101.

If Q101 is still working properly, B+ voltage should be lower and the R103 voltage obviously higher when Q102 is removed. If Q101 is defective, not much will change.
 
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Hi again, result! I removed Q102 and as you said no change, so I took Q101 from the other chassis and fitted it to this one and hey presto the B+ is 78v, but Q102 is still removed so maybe I should refit that and see what we have?

Many thanks this has been great help from you, I really appreciate you taking the time to help me

Ronnie
 
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Can you check the voltages on the 3 pin's of Q204?

If that one is defective and not pulling the base voltage of Q102 down, Q102 could be fine.

emitter of Q204 should be approx 33V (As you measured that on the zener.)
 
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obcd said:
Can you check the voltages on the 3 pin's of Q204?

If that one is defective and not pulling the base voltage of Q102 down, Q102 could be fine.

emitter of Q204 should be approx 33V (As you measured that on the zener.)
Click to expand...

Will do tomorrow and report back.

Thanks again

Ronnie
 
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Now you should measure the base - emitter voltage of Q204. Base should be 0.7V higher than emitter. If that's the case, Q204 is probably defective as it's collector voltage should be lower.

If it's not the case, the voltage divider being R214 R278 R213 R212 R211 could be having a problem, but I put my money on Q204 for the moment. If you adjust R212, collector voltage should change. Base emitter will be constant as transistors are current driven.
 
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