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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions. |
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25th Sep 2016, 1:32 am | #1 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Pineapple 625/405 converter.
I'm presently servicing a Pineapple standards converter. The problem we're having is black level shifts and sync pulse crushing.
For test purposes the converter is supplied with video from a DVD player, the fault is not apparent on a test pattern. My attention was first drawn to IC U14, a 74HC4066 quad bi-directional switch. First check the black level clamp, pins 6,8 and 9. The 9uS clamp pulse is present at pin6, adjustable DC reference present at pin 9. Video sans syncs present at pin 8. Inverted mixed blanking present at pin 13. Mixed syncs present at pin 12. Fixed sync tip reference present a pin10. A good test point to monitor the composite video is at the emitter of Q8, the video signal is correct. Move on to the final amplifier stages which consist of transistors Q9, Q10 and Q11. The fault is apparent at the emitter of Q11 and the load resistor R49. It seems that the input stage of the modulator is causing the fault, black level shifts when the picture content changes and also sync crushing. So now my attention when be on the RF modulator module. DFWB. |
26th Sep 2016, 9:34 pm | #2 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Re: Pineapple 625/405 converter.
It is in fact the modulator that is causing all the problems. The modulator is the type made by W. Meier in I believe Germany.
I have no circuit information for this unit. Visible from the top side of the PCB there is a 45Mhz crystal controlled oscillator which employs a BF245 FET. A 78M05 5 volt regulator IC. A few capacitors and resistors, two coils, one I assume is the 41.5Mhz oscillator for the sound carrier. On the print side of the PCB is a single surface mounted IC of an unknown type. The modulator is contained in a 70 X 70 X 30mm metal box. DFWB. |
28th Sep 2016, 4:21 pm | #3 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Re: Pineapple 625/405 converter.
Some good news about the Pineapple converter. The video amplifier part is supplied from an 8volt source, or should be. The two resistors associated with the LM317 regulator had changed in value, thus reducing the supply to just under 7 volts. Also, there was a 15ohm series resistor between the 20 volt supply and the input pin of the regulator. I've reduced it to 10ohms. So now we have exactly 8 volts for the video amplifiers and what a difference that has made. No more sync crushing. For test purposes the modulator part of the Aurora is being used to supply signal to the TV receiver.
Switch No.6 sets the Aurora to modulator only. DFWB. |
28th Sep 2016, 5:12 pm | #4 |
Nonode
Join Date: May 2006
Location: St Albans, Herts, UK.
Posts: 2,193
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Re: Pineapple 625/405 converter.
Nice to see you keeping a first generation "home" standards converter operational.
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All the very best, Tas |
29th Sep 2016, 8:29 pm | #5 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: Pineapple 625/405 converter.
Hi Taz,
the Pineapple can give a good account of itself. It's an unusual device in the sense it is a field store converter. Works well on VHS. The final stage of this converter repair is to sort out the modulator unit. It was made judging by the date codes on the components in the year by 2000 W. Meier in Germany. The intriguing thing about this modulator is that a single IC is employed for vision and sound. The sound it would seem to be have been modulated on a 3.5Mhz carrier and is we believe to be FM and not AM as it should be. Possibly the reason for the poor quality sound. The attachment shows the circuit diagram of the modulator. DFWB. |
1st Oct 2016, 2:28 pm | #6 |
Hexode
Join Date: Jan 2005
Location: Waterford, Republic of Ireland
Posts: 259
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Re: Pineapple 625/405 converter.
It's going on my headstone: I told you it was the power supply!
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1st Oct 2016, 10:27 pm | #7 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: Pineapple 625/405 converter.
Hi Andy, The supply to the video amplifier stages is 8 volts so even a drop of only 1 volt is sufficient to impair the performance.
DFWB. |