#1
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1985 toshiba blackstripe has no vert. hold?
I just was given my dads old toshiba blackstripe color tv, and
it has no vert. hold, after 15-30 minutes of warmup, the vertical works, but none at first what could i do to fix this, i have cleaned the control
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Looking for zenith cobramatic parts -johnny the raster master! |
#2
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get a schematic, look for parts like resistors in the hold circuit, heat or cool them and see what happens.
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#3
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Why did you think cleaning a control would help if its clearing up by itself with run time, cleaning make no sense? You need to apply some critical thinking to your troubleshooting skills.
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#4
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From my own experience with a Blackstripe from Dec of '84 (and tips I've read on this forum), look for a couple of 2.2uF 50V electrolytic caps near a big 42 pin IC. These caps need to low be ESR and as they age, the ESR tends to go up and cause problems. As a temporary fix, since I didn't have the right cap, I used a 2uF film cap and it solved the roll issue. Another trick when working without a schematic, is do a google search on the ICs. The big 42 pin IC in my set is a TA644. Examining the data sheet shows pin 28 is connected to the vertical ramp capacitor, and the typical application drawing in the datasheet shows this pin connected to a 2.2uF cap.
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#5
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Also if the set has small stand up boards on the main chassis
pull them & resolder the pins that joint the boards. ( the boards are soldered in !! ) I dont remember vert roll but they will cause hoz sync & intermitant sound. Very common problem, after the first few all Toshibas got reworked to prevent recalls. good luck |
Audiokarma |
#6
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Spinning head - is right, and its a good idea to take down the ic number get the data sheet and use the pinout to figure out whats going on, Good job! I fixed a few sets without schematics doing that with tube sets and a tube manual, and modern sets with ic chips in them.
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Yes you can call me "Squirrel boy" |
#7
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In reference to DaveWM's comments regarding radiotron's Toshiba Blackstripe TV with vertical hold issues: You are correct -- cleaning the hold control potentiometer will not in and of itself correct the vertical hold problem. The problem is likely caused by a drifting resistor in the vertical circuits; as the set warms up, the resistor gets closer to its proper value (as the part itself warms up) until it is of the correct value to lock in the vertical. The set will operate normally thereafter, until it is turned off and gets cold; however, when the TV is turned on again and until the resistor warms up, the trouble will return. I'd look for that drifting resistor and replace it, before it gets to the point where it may not return to its rated value even after the set warms up. Problems like this almost always get worse with time, if not corrected.
I don't know for sure, but that set seems like a mid-to-late '80s model, making it close to thirty years old. Any TV that old will have dirty controls (most sets of that vintage still used rotary potentiometers for vertical hold, brightness, contrast, etc.), so a good cleaning can't hurt anything.
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Jeff, WB8NHV Collecting, restoring and enjoying vintage Zenith radios since 2002 Zenith. Gone, but not forgotten. |
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