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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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11th May 2016, 5:28 am | #1 |
Heptode
Join Date: Sep 2014
Location: Coventry, West Midlands, UK.
Posts: 518
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Regentone 17 - 18 frame collapse
This set has been used more or less daily for the last 2 years since I got my aurora. It has worked fine, apart from the occassional frame jitter,until yesterday evening. I switched on and it came on fine then after a couple of minutes it started to jitter and roll and then the frame collapsed. I tried a new 30pl13 and ecl8o,frame output and frame oscillator, to no effect. So left it for a while then took some voltage measurements. There was no voltage at pin 9 of the 30pl13. Looking at the circuit that gets its voltage from the boost line via the height control and a couple of resistors. So checking back along the supply line suspicion has fallen on r64,680k,(manufacturers manual), voltage at one end nothing at the other. Sods law then came into action among all the resistors I have I don't have one of that value. I have now ordered some.
Assuming that this resistor is the culprit could the occassional jitter be due to the slow breaking down of it? The set has been completely re capped. Thanks Steve |
11th May 2016, 6:34 am | #2 |
Heptode
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
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Re: Regentone 17 - 18 frame collapse
Hi Steve,
I have Trader Sheet 1478 in front of me, the component references might be different, so have a look at that if you can. On the trader sheet, Pin is connected to R54 (8K2), which is in series with R64 (820K) and the height control R63 (2M), which in turn is connected to R65 (470K) over in the line timebase. Note that I can't find a 680K resistor, but it is posible that if R64 is the same component in both circuits that the value was changed in production to change the range of the height control. Have you been able to measure the resistor? It is worth checking the three capacitors connected to the junction of R54 and R64 - C53 (0.04uF), C54 (0.05uF) and C58 (0.003uF), with C53 being the most likely candidate to have killed off R64. Usually such intermittant faults that suddenly become permanent are assosiated with faulty caps, but it can happen to resistors. If you can imagine the resistor stretched out as a long resistance wire (even though it is not made that way), if part of that wire becomes thinned and weakened, then the resistance at that point will go up, the voltage across it will go up, causing the wattage to go up at precisely the point where the resistance material is thinnest (so less able to handle wattage). So in high stress conditions a noisy resistor can quickly become an open circuited one. The value of the resistor in series with the height control is not that important for testing purposes as you have 2M of height control to play with, so something in the right ballpark will do for now. How it works... The sawtooth is derrived by charging up C53 via R64 and the height control. C53's earthy end is connected to the cathode of the frame output stage to provide some negative feedback. When the multivibrator flips over then C53 is discharged via R54, where R54 sets the flyback time. C54 couples the sawtooth to the grid of the output stage, but has little effect on timing due to the high value of the resistances around the grid part of the circuit. I hope that helps. Cheers Andy
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11th May 2016, 8:17 am | #3 |
Heptode
Join Date: Sep 2014
Location: Coventry, West Midlands, UK.
Posts: 518
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Re: Regentone 17 - 18 frame collapse
Hi Andy
thanks for that and you are right! It is 820k a senior moment there. I checked and I had ordered 680k too so have now ordered the right ones. My brain hurts I think I will go lie down lol Steve |
22nd May 2016, 7:07 am | #4 |
Heptode
Join Date: Sep 2014
Location: Coventry, West Midlands, UK.
Posts: 518
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Re: Regentone 17 - 18 frame collapse
I finally got to have a look at this TV. I replaced R64 820k still no voltage at pin 9 of the 30PL13 so tried the caps C53 and C54 both 0.05uF still no joy. So did some more votage checks. There were no volts at pin 1 anode of the triode section of the ECL80. R70, 27k, was open circuit. Replaced it and full frame was back. I have to fit the replacement components properly, I just tacked them on for trial, but it's now working OK again but still have the occassional frame jitter. I think it may be down to poor connection on the frame height or linearity controls as they are very sensitive and if you touch them things jump or move dramatically. I am not sure of the best way to open these as they have those awkward clips holding them together and I don't want to break the shaft off trying to do so.
Steve |