Re: Star Wars 25 inch Amplifone issue

If you use the isolation/booster transformer, avoid boost unless you have
no other choice.
On Sep 27, 2013 2:06 PM, "Rodger Boots" <rlboots2@gmail.com> wrote:

> Isolation used to be done with an isolation transformer. These are
> getting hard to find.
>
> Do NOT recommend tapping on the neck or the "blow the short out"
> techniques---not for heater-cathode shorts.
>
> See EBay item 150546845743.
> On Sep 27, 2013 1:43 PM, "Ken Sumrall" <k_lists@scrapheap.net> wrote:
>
>> And Rodger guessed correctly. Sad face for me. :-(
>>
>> After probing around with a scope, and checking signals, it became clear
>> something was going on in the tube. So we swapped the blue and green
>> drive wires in the connector, and powered it back up. If the issue was
>> with the electronics driving the tube, we expected the overall gree hue
>> would become blue. And if the problem was in the tube, it would stay
>> green. And it stayed green.
>>
>> After some research, we found this:
>>
>> http://www.repairfaq.org/**REPAIR/F_monfaqa.html#MONFAQA_**002<http://www.repairfaq.org/REPAIR/F_monfaqa.html#MONFAQA_002>
>>
>> And it looks like our three choices are:
>> 1. Tap the neck (gently) with the crt face down and try to dislodge the
>> short.
>>
>> 2. Try blowing the short out (with a current pulse), but this risks
>> blowing out the heater filament too. I have a Sencore CR-70 which I
>> recently acquired, but I've not yet powered it on. And the manual says it
>> doesn't clear heater-cathode shorts because it can blow out the filament
>> too.
>>
>> 3. Remove the ground reference from the filament and float it.
>>
>> The last option sounds intriguing. Does anyone think this is a bad idea?
>> Do I need to worry about improving insulation on the heater winding or
>> wires to the CRT? IIRC, the cathodes are only about 180 volts, so I think
>> the insulation on the wires will be sufficient. Will the floated voltage
>> on the wires affect other coils in the flyback? If so, we could create a
>> separate power supply for the heater.
>>
>> Comments? Suggestions?
>>
>> ___
>> Ken
>>
>>
>> Rodger Boots wrote:
>>
>>> Heater-cathode short in CRT green gun? Don't suppose you have a CRT
>>> tester?
>>>
>>> On Sep 11, 2013 6:10 PM, "Ken Sumrall" <k_lists@scrapheap.net <mailto:
>>> k_lists@scrapheap.net>**> wrote:
>>>
>>> The monitor on our Star Wars sit down machine at work is having
>>> issues. It started with an intermittent issue where the screen
>>> would suddenly turn green, and it was very bright and all the
>>> retrace lines were showing, and all the lines were out of focus.
>>> Smacking the cabinet would sometimes bring back a good picture.
>>> Then we also lost vertical deflection, so we opened it up to take a
>>> look.
>>>
>>> The deflection issue was easy to fix. We replaced a few
>>> transistors, and a fuse, and it was working again. The other issue
>>> we're still struggling with, in fact it's much worse, and is mostly
>>> in the bad state, with occasional flickers of it working correctly.
>>>
>>> We initially thought it was a bad connection in the CRT socket, as
>>> it seemed to change as I was poking the socket with a wooden stick.
>>> So I replaced the CRT socket harness with a spare one I had. That
>>> didn't work. So poked some more, and started to think there was a
>>> loose connection in the focus block. But then poking further didn't
>>> do anything.
>>>
>>> So, we started to suspect that something is just randomly working
>>> for short moments, and whatever I was poking when that happened made
>>> me think that was the issue.
>>>
>>> We are now wondering if maybe the green drive transistor is shorted
>>> on? That would explain everything looking green, and the retrace
>>> lines, and the brightness. Would that also explain the poor focus?
>>>
>>> Any other suggestions?
>>>
>>> Thanks!
>>>
>>> ___
>>> Ken
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>>
>

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Received on Fri Sep 27 15:12:46 2013