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Measuring CRT heater voltage?    
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70runner



Joined: 17 Sep 2014
Posts: 3
Location: SOCAL

PostPosted: Thu Sep 18, 2014 1:59 am    Post subject: Measuring CRT heater voltage? Reply with quote

Retired EE but no sparky so be gentle Smile Restoring an Atari Star Wars arcade game (upright) that uses a 19" amplifone CRT. The game was working, though with some horizontal distortion. The HV and deflection boards were mucked up by previous repairs. Rebuilt using reproduction boards with new components where possible, incl new FBT. Have good HV, 19.5KV at the anode, but no CRT neck glow, and spot killer LED is on. All supply and circuit voltages check OK, game plays in the blind.

CRT heater voltage measures at 1.2VAC by Fluke 115 RMS meter and 4.0VAC by Simpson 270, both short of the required 6.3VAC. Used Simpson because folks on arcade/amplifone forums argue analog meter is more accurate for heater measurement. I trust the Fluke. Is there a preferred method to accurately measure heater voltage?
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JTS1957



Joined: 21 Jan 2009
Posts: 2286
Location: Far, Far Away

PostPosted: Thu Sep 18, 2014 12:51 pm    Post subject: Reply with quote

I assume the CRT lights normally using a Picture Tube Tester?

According to quick scan of monitor's service literature, Spot killer LED should NOT be illuminated in normal operation.

Read this:
www.elektrotanya.com/files/forum/2014/03/kepcsofutes-mero_[ET].pdf
70runner



Joined: 17 Sep 2014
Posts: 3
Location: SOCAL

PostPosted: Thu Sep 18, 2014 1:59 pm    Post subject: Reply with quote

Don't have access to a picture tube tester. You are correct about the spot killer. I'm assuming the spot killer is on because there is insufficient heater filament voltage.

Thx for the link. Good reading, but I trust the Fluke 115 reading.
JTS1957



Joined: 21 Jan 2009
Posts: 2286
Location: Far, Far Away

PostPosted: Thu Sep 18, 2014 2:41 pm    Post subject: Reply with quote

Page 8 of monitor service manual explains spot killer's operation in detail.
kuhurdler



Joined: 28 Dec 2006
Posts: 2852
Location: Overland Park, KS

PostPosted: Fri Sep 19, 2014 7:26 am    Post subject: Reply with quote

page 8 of this: http://falz.net/files/starwars/amplifone_service_manual.pdf

and there's also this: http://falz.net/files/starwars/amplifone_faq_1_2.pdf
(and this)
http://falz.net/files/starwars/atari_vector_repair/#VATARI_035
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70runner



Joined: 17 Sep 2014
Posts: 3
Location: SOCAL

PostPosted: Sat Sep 20, 2014 8:02 pm    Post subject: Reply with quote

Thx for the links. I've been through all these docs, even have hard copies. At one point I thought the no filament glow was related to the spot killer, but believe they are separate issues.

I've reinstalled my old FBT to see if that solves the heater filament issue. I've checked all the major components of the deflection board, especially the spot killer circuit, everything looks good. Next step is to check the deflection bd inputs to verify XY signals.
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