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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 27th Oct 2015, 8:47 pm   #1
chompy1
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Default Toshiba Portable TV (C-1480B)

Hi Guys,
I started on this set on Saturday. The LOPT is producing no HT whatsoever and the CRT heater won't glow and there is no audio output either. The LOP transistor has tested good on the meter as does the CRT heater filament. Unfortunately I don't have a circuit diagram. Your help and advice will be much appreciated. Thanks in advance, Paul
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Old 27th Oct 2015, 9:30 pm   #2
chompy1
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Default Re: Toshiba Portable TV (C-1480B)

forgot to mention that several LOPT pins are shorted to earth and the chassis is receiving power.

Thanks, Paul
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Old 27th Oct 2015, 9:51 pm   #3
1955APREN
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Default Re: Toshiba Portable TV (C-1480B)

Hi Paul
Is the loptx used in this set a Philips type, possible grey and black casing. If so these were very prone to going s/c. Can you trace out the HT+ line into the Loptx and disconnect this pin, then measure the voltage. If this is ok (108v /112v) the loptx is faulty.
Regards
Derrick
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Old 27th Oct 2015, 11:53 pm   #4
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Default Re: Toshiba Portable TV (C-1480B)

Bear in mind a lot of the low voltage supplies are derived from the LOPTx so these will read low resistance to chassis. The important one to check is the HT (B+)connection and the connection to the output transistor, check from collector to chassis, if this reads a short the transformer is probably dud (assuming the transistor is ok as you mentioned).

If there's no short, do you get any voltage at the collector? Normally you won't be able to measure this as when working it's high frequency spikes and a meter will object, if you get steady HT however there is no line drive.

Without the line output stage running there will be no sound as the supplies are missing.
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Old 28th Oct 2015, 12:28 am   #5
chompy1
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Default Re: Toshiba Portable TV (C-1480B)

thanks guys.The LOPT casing is white. I will try out your tips tomorrow evening and report back. Cheers, Paul

Last edited by chompy1; 28th Oct 2015 at 12:41 am.
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Old 28th Oct 2015, 10:13 am   #6
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Default Re: Toshiba Portable TV (C-1480B)

These are super reliable receivers and the fault is only going to be something simple. I sold many of them new.
I will have a look through my Toshiba data. It is 100% Japanese with a non Philips LOPT.
I think the power supply is a linear regulator from memory that is! John.
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Old 28th Oct 2015, 9:33 pm   #7
chompy1
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Default Re: Toshiba Portable TV (C-1480B)

thanks John. As these sets are very reliable, is there a good chance that the LOPT is ok? Cheers, Paul
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Old 29th Oct 2015, 9:11 am   #8
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Default Re: Toshiba Portable TV (C-1480B)

Hello Paul,
Yes the LOPT will be fine and so will the tube [unless of course the neck is broken off!] I think I may have the original manual for this and will have a look over the weekend.
It will be in the garage on a rack behind the Land Rover that has decided after 42 years that it's clutch master cylinder has done it's duty...
I will drag the old soldier out on Saturday. Regards, John.
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