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

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Old 25th May 2020, 7:12 pm   #21
FERNSEH
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Default Re: Sharp TRP801

The +12volt supply for the IF amplifiers and tuner is derived from the line output transformer. Because the line output stage doesn't work the power supplier has been connected direct to the IF board. All the transistors are PNP types and the circuits are of the "upside down" type, that is, the supply rail is positive and the transistor collectors are connected to near ground potential.
The vision IF amplifier doesn't work but at least the sound IF amplifier does and is delivering almost 4 volts P - P of audio across the detector load resistor.
The sound intermediate frequency has been determined to be 14Mhz and this will be the frequency for both TV standards. The AVC is efficient, maintaining a constant voltage across the load resistor irrespective of signal levels.

DFWB.
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Old 25th May 2020, 8:37 pm   #22
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Default Re: Sharp TRP801

That is a very interesting TV David. At a quick glance it has an English Emerson look about it, very American.
We never thought transistors would fail but I suppose 60 years on we can forgive them. There can't be many transistor portables of this era that have survived.
When they went wrong they were just dropped in the garbage. That is the problem with small items. Hope you get it sorted. John.
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Old 26th May 2020, 12:43 pm   #23
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Default Re: Sharp TRP801

Hi John,
It's likely an NTSC version was made for the American and Japanese markets.
The attachment shows the additional tuning and damping components added across the primaries of the vision IF transformers.

DFWB.
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Old 26th May 2020, 4:55 pm   #24
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Default Re: Sharp TRP801

Some very careful soldering there to avoid track bridging.
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Old 26th May 2020, 5:32 pm   #25
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Default Re: Sharp TRP801

"Some very careful soldering there to avoid track bridging."

Hi Glyn,
All the soldering must have been done by hand rather than by an automated flow system. Wouldn't have been very pleasant working conditions.

DFWB.
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Old 20th Jun 2020, 12:52 pm   #26
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Default Re: Sharp TRP801

Found a plug for the mains input so now work can restart on the set.
The receiver is on the bench right now and connected to the mains. The line oscillator is working and the line output transistor will be reconnected into the circuit. The line output stage supplies power to the signal circuits.

DFWB.
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Old 20th Jun 2020, 5:23 pm   #27
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Default Re: Sharp TRP801

The lead connecting to the base of the line output transistor has been resoldered so now the line output stage is active. A negative going pulse of 65 volts is present at the collector of the line output transistor. This will no doubt increase when the scanning coils are reconnected. The good news is that a spark is present at the anode of the EHT rectifier. The sound IF amplifier is working and so is the tuner unit, at least I assume it is because clicks can be heard when the tuner knob is turned.

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Old 20th Jun 2020, 11:09 pm   #28
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Default Re: Sharp TRP801

The sound IF channel is working but the vision IF amplifier isn't. Six 2SA234 PNP transistors are employed in the vision IF stages. Voltages on stages 3 to 6 are close to the correct figures but the AGC controlled first stage transistor has no base and emitter voltages. Fault traced to an electrolytic capacitor in the AGC circuit gone short circuit.

DFWB.
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Old 22nd Jun 2020, 4:21 pm   #29
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Default Re: Sharp TRP801

The 100mfd capacitor has been replaced and now the vision IF amplifier is working again. Oscilloscope waveform was taken at the anode of the 1N60 vision detector diode.
The UHF tuner operates in the 625 standards switch position.

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Old 4th Jul 2020, 5:30 pm   #30
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Default Re: Sharp TRP801

Today, I decided to refit the CRT and wire up the scanning coils. Plenty EHT and the tube is displaying a bright thin horizontal line, at least there's some video activity in the line proving that the video amplifier is working.
Operated the system switch while the set was working, bad move, killed the line output transistor. It's a 2SB275, PNP germanium type.
https://www.radiomuseum.org/tubes/tube_2sb275.html
An AU113 will serve as a replacement.

DFWB.
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Old 5th Jul 2020, 6:40 pm   #31
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Default Re: Sharp TRP801

Operating that system switch also killed the frame output transistor.
It's a 2SB84, the Radiomuseum suggests the ASZ16 as an equivalent.
As a temporary measure an AD149 has been fitted. Looking at the amplitude of the flyback pulse it's unlikely the transistor will last very long in this application. The collector load consists of a choke and the high impedance scanning coils connected in parallel.
Imagine what the flyback pulse would be without the scanning coils?
The waveform will corrected after the output bias is adjusted. The PNP transistor is cut-off at the start of the scan.

DFWB.
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