Atari Amplifone focus snapping in and out.

[TheGeekPub]

I have an Atari Star Wars with a 19" Amplifone vector that is snapping in and out of focus.

Symptoms: Starting from a sharp focus the monitor will slowly (over about 3 to 4 seconds) get blurrier and blurrier until it instantly snaps back into sharp focus. Repeat.

I have replaced the flyback with one from ArcadePartsandRepair and recapped the HV board. No change. There is an article in Gregg Woodcocks' amplifone guide, that matches the symptoms almost 100%, but I opening the neck connector and checking it doesn't seem to reveal the issue he said to look for.

Any ideas CRT friends?

 

[andrewb]

Make sure your dag spring exists, is making clean contact to the tube, as well as the metal tube mounts, and that it's grounded.

 

[TheGeekPub]

I assume this is the dag spring.



I checked with the meter and it does have continuity to the metal frame and the pin goes to the cup connector. Thanks for the suggestion!

 

[andrewb]

Ok. Check the tube pins as well. Focus going in and out can mean a bad or weak connection between the flyback and tube. Make sure they are clean and straight.

Also, remove the two rubber boots in the back of the focus block on the hv board and make sure the joints are solid where the wires meet the tab on the block.

Those are almost always frayed and weak, and need to be redone on these. If they are frayed or floppy at all, desolder, strip back to fresh wire, and resolder them.

 

[TheGeekPub]

OK. So I have checked the connections and re-soldered the focus block just to make sure and the symptoms are the same. Focus is sort of pulsing over time.

This does make me wonder though. The flyback is from APAR, but the best focus is basically with the flyback focus knob turned all the way up. Someone told me to remove or add a loop on the heater wire/core. Think that's related?

 

[andrewb]

OK. So I have checked the connections and desoldered the focus block just to make sure and the symptoms are the same. Focus is sort of pulsing over time.

This does make me wonder though. The flyback is from APAR, but the best focus is basically with the flyback focus knob turned all the way up. Someone told me to remove or add a loop on the heater wire/core. Think that's related?

No. You should have three loops of wire on the ferrite for an Amplifone. The flybacks used to come with four, so you had to remove one. But the ones I've gotten more recently have had three, and I haven't had to remove any. However that controls the heater voltage, not anything to do with the HV.

Also, some flybacks out there need the knob turned to max to get focus. However that was mostly the ones from Arcadeshop. (There's a thread here about them.) I don't think I've seen that from an APAR flyback. But you might have a bad one, that's always possible. Or a bad focus block.

If it were me I'd swap out the fly, just to see. But I'm guessing you probably don't have a spare.

 

[TheGeekPub]

Actually, I swapped the factory flyback because I thought it was bad and causing this. Only to find the new flyback didn't fix anything.

I already searched for a focus block. Know where to find one?

 

[andrewb]

What kind was the factory flyback? Was it a Wintron? Those rarely fail, and are better than the repros.

Take a DMM and tone out the wire between the focus block and the neck socket. It sounds like there's a break somewhere, and it's arcing, which is causing the snapping back. Ideally you want to make sure there's continuity all the way to the tube pin (which can be hard to confirm, as you'd need to get a probe or thin wire onto the tube pin, if you can back the socket off enough to get a small wire in there, wrapped around the pin.)

Also, have you tested the HV level at the anode? (Do you have an HV probe?)

 

[TheGeekPub]

I keep some tiny 30 gauge wire around just for this kind of test. Yes. with wire wrapped around the pin and neck socket in place I get continuity all the way to the focus wire on the back of the block.

I don't have a HV probe. I keep telling myself to order one and then never do it for some reason.

Man, I have to tell you thank you for all this direction. Super appreciated!

 

[bakerhillpins]

I've had APAR flybacks that did not focus and that's documented in my giant HV thread. If you have an OEM Big Red flyback keep using it IMHO.

Is Q3 a BU406D (The D suffix is important).

How did you check the pins in the big white neck connector? Did you open up the clamshell and look inside? Makes me wonder if the focus pin has broken loose on the end of the tube and the white keying cap is sorta holding it in.

 

[TheGeekPub]

How did you check the pins in the big white neck connector? Did you open up the clamshell and look inside? Makes me wonder if the focus pin has broken loose on the end of the tube and the white keying cap is sorta holding it in.

Yep. I opened the neck socket and checked all of the pins inside. It comes into three pieces.

 

[andrewb]

You really should have an hv probe. You have zero idea what your hv is set to otherwise.

 

[TheGeekPub]

You really should have an hv probe. You have zero idea what your hv is set to otherwise.

OK. You're right. Do you have one you can recommend and I'll get it on order.

 

[andrewb]

You can get a used Fluke 80k-40 (ebay), or a new BK Precision PR 28A. They're basically the same thing. (The BK is a knockoff of the Fluke.)

Either will run you under $100.

 

[KaBoom1701]

This one has served me well.

High Voltage Probe 40,000 Volts Max DC, 28,000 Volts Max AC (50/60 Hz)

•40,000 volts max DC.•28,000 volts max AC (50/60 Hz)•1,000M input impedance.•Accuracy DC: +/- 1% to 20KV +/- 2% to 40KV AC: 5% to 10% (50/60 Hz)•Division ratio 1,000:1•For 10Mohm input impedance DMM (Accuracy <0.5%) only

www.elexp.com

Plugs right into my Fluke 117