15-08-2020, 07:18 PM
(This post was last modified: 15-08-2020, 07:21 PM by Murphyv310.)
Hi.
Here we have the circuits of the two different TV timebases and a rough idea of what to do.
I will explain as best as possible.
On the Murphy firstly remove the LOPT, U26 holder and EHT lead. If the original LOPT is not going to be salvaged just snip the leads as close to the LOPT as possible, Remove one PK screw that holds the LOPT bracket at the lower part of the line TB section and remove the bracket.
On the 900 LOPT remove the LOPT from the bracket and remove the lip on the bracket by simply bending it off, dress the rough edge with a file. Turn te bracket upside down and fit refit the LOPT to the bracket, you'll need two thin washers under the LOPT to the bracket to compensate for the recessed holes on the bracket, as the LOPT wont sit properly without them. The LOPT can be mounted in the angled section of the chassis with two PK screws, make sure it is mounted to clear the the removable cover. How you want to do the EHT diodes is up to you. I used a little pick up cartridge box and potted three diodes and the cap with hot melt done in layers.
Once fitted now do the following. The 30P19 anode goes to "E" on the jellypot, using the blue lead, the U193 cathode goes to "D" using the Yellow lead. The Gray lead from the scan coils go to "A" not L39 but the LOPT end of the choke. Red/White goes to "C" on the jellypot. Fit a 330pf 2kv cap between "A & B" of the jellypot. Remove the following leads from the set that you have cut Brown, Green & White from their respective components.
Remove R316 220k. Follow the 900 circuit for the stabilised EHT, I used 100pf pulse caps for C105 & C106. R129 is 1.5m, R133 is 820k which goes to "A" on the new LOPT. The VDR has a green paint spot on one end, it is not polarity conscious. You need 25-40v negative volts for the linearity control, where you removed R316, on my set the mains dropper was partially O/C and the rectifier supplies negative volts to the heaters so I just tapped off around 60v fed this via a 18K resistor to a 100uf cap with a 30v zener across it to give -30v for the control. Lastly add a 0.22uf 250v cap for "S" correction in series with the Grey lead from the scan coils.
Time to check the work and test. I advise using a variac set to 160v initially, gradually increasing it once scan is seen. If all goes well at 180v the width control will hold the width constant with rising input volts.
Hope this all helps
Here we have the circuits of the two different TV timebases and a rough idea of what to do.
I will explain as best as possible.
On the Murphy firstly remove the LOPT, U26 holder and EHT lead. If the original LOPT is not going to be salvaged just snip the leads as close to the LOPT as possible, Remove one PK screw that holds the LOPT bracket at the lower part of the line TB section and remove the bracket.
On the 900 LOPT remove the LOPT from the bracket and remove the lip on the bracket by simply bending it off, dress the rough edge with a file. Turn te bracket upside down and fit refit the LOPT to the bracket, you'll need two thin washers under the LOPT to the bracket to compensate for the recessed holes on the bracket, as the LOPT wont sit properly without them. The LOPT can be mounted in the angled section of the chassis with two PK screws, make sure it is mounted to clear the the removable cover. How you want to do the EHT diodes is up to you. I used a little pick up cartridge box and potted three diodes and the cap with hot melt done in layers.
Once fitted now do the following. The 30P19 anode goes to "E" on the jellypot, using the blue lead, the U193 cathode goes to "D" using the Yellow lead. The Gray lead from the scan coils go to "A" not L39 but the LOPT end of the choke. Red/White goes to "C" on the jellypot. Fit a 330pf 2kv cap between "A & B" of the jellypot. Remove the following leads from the set that you have cut Brown, Green & White from their respective components.
Remove R316 220k. Follow the 900 circuit for the stabilised EHT, I used 100pf pulse caps for C105 & C106. R129 is 1.5m, R133 is 820k which goes to "A" on the new LOPT. The VDR has a green paint spot on one end, it is not polarity conscious. You need 25-40v negative volts for the linearity control, where you removed R316, on my set the mains dropper was partially O/C and the rectifier supplies negative volts to the heaters so I just tapped off around 60v fed this via a 18K resistor to a 100uf cap with a 30v zener across it to give -30v for the control. Lastly add a 0.22uf 250v cap for "S" correction in series with the Grey lead from the scan coils.
Time to check the work and test. I advise using a variac set to 160v initially, gradually increasing it once scan is seen. If all goes well at 180v the width control will hold the width constant with rising input volts.
Hope this all helps
