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Old 23rd Jun 2020, 12:15 am   #21
bionicmerlin
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Default Re: Marconi 1400 birthday present

Iím plodding on slowly.
As the original UHF tuner was iffy I decided to use a replacement from a scraped 1400. As itís a later tuner I had to do the normal repairs on the presets.
Iím still not happy with the width but I did read on John Laws fault finding guide C114 high voltage cap can affect the width. Also on John (HCS )notes he says if itís not a disc type to replace it.
Also a new fault now ,I get intermittent frame collapse .im still working on that . Again on Johns notes he says check tags on FOPT they look ok to me. Maybe I will re solder anyway.
Any more help appreciated.
Picture of set on 405 and now 625 Andy
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Old 23rd Jun 2020, 1:27 am   #22
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Default Re: Marconi 1400 birthday present

Please take extreme care in replacing C114. The Lopt can be easily ruined through too much heat from the iron. I ruined a perfectly good Lopt once.

The frame output transformer is quite a weight on a PCB so dry joints are inevitable here. A stubborn case of intermittent frame collapse was once traced to a hairline fracture on the PCB close to the Frame output transformer tags.

It's looking good, well done.
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Old 23rd Jun 2020, 8:21 am   #23
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Default Re: Marconi 1400 birthday present

looks good! That lack of width with poor line lin looks like a classic case of the linearity sleeve being pushed in about an 1/8th of an inch too far. Worth a check. John.
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Old 23rd Jun 2020, 9:03 am   #24
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Default Re: Marconi 1400 birthday present

Are you sure you've not got the narrow test card? I down ages trying to get my vt4 width up but it turned out that my aurora had an odd test card flashed to it from new.
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Old 24th Jun 2020, 1:44 am   #25
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Default Re: Marconi 1400 birthday present

Thanks everyone. I have changed C114 being very careful.
No difference to the picture. It looked like I will have to have a go with the linearity sleeve . Everything’s a bit tight so I will very careful.
Dominic my test cards work ok on my other TVs ok I got them on dvd with music thanks anyway Andy
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Old 25th Jun 2020, 5:18 am   #26
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Default Re: Marconi 1400 birthday present

Have a similar width problem with the 16" Ferguson Courier III I have. I haven't plucked up the courage to replace C114 yet. I'll check the linearity sleeve when I get a chance to have another look. The set otherwise works very well, but had to write off the system switch solenoid and change systems manually.

Had this problem on another set which was due to wear on the system switch tags that activates the solenoid. On that occasion, replacing the switch sliders solved the problem. Unfortunately, the chances of finding a replacement nowadays will be very difficult.
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Old 25th Jun 2020, 8:28 am   #27
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Default Re: Marconi 1400 birthday present

Cut the leads on the old ceramic, wrap the leads of the new cap around the post and solder. It's all too easy to rip the post out of these Jellypots.
Note the value of it depends on the model and the EHT tray fitted. 20KV versions usually have a 220pf, 16kv 160pf but check. Too higher value will give low EHT and excessive width, too low will give excessive EHT and lack of width with possible damage to the EHT tray. The same applies to the 1500 of course. John.
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Old 27th Jun 2020, 8:01 am   #28
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Default Re: Marconi 1400 birthday present

Excellent advice there John as always. I ran the set up yesterday and was reminded of another common problem of weak signals due to a break in the UHF isolated coax socket, confirmed by wriggling the plug. Will sort that out over the next few days now I have a week off.

Speaking of these capacitors, one thing that was immediately evident when I adapted the 960 to take a 1400 Lopt when the original red one failed was lower EHT, this with a 160pf cap.. The regulation isn't very good either. Might try experimenting with the values of the disc capacitor to get it to normal levels.
Cheers
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Old 28th Jun 2020, 2:13 am   #29
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Default Re: Marconi 1400 birthday present

I have now changed C114 220pf . Not made any difference. Infact I found out the original had been changed before with a second hand one .the original was stuck in the air slots at the bottom of the cabinet.
I dicided to try repositioning the linearity sleeve only to find it stuck on with glue one side. After freeing it up it dosnt do a thing . Iím not sure how it works it looks like just a piece of plastic or should their be something in the recessed bit. Sorry Iím a bit vague . I might have a spare on a scrap set .heres a picture showing some of the glue. Andy
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Old 28th Jun 2020, 7:04 am   #30
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Default Re: Marconi 1400 birthday present

Quote:
Originally Posted by bionicmerlin View Post
I decided to try repositioning the linearity sleeve only to find it stuck on with glue one side. After freeing it up it dosnt do a thing . Iím not sure how it works it looks like just a piece of plastic or should their be something in the recessed bit. Sorry Iím a bit vague . I might have a spare on a scrap set .heres a picture showing some of the glue. Andy
Look at the photo in post 11.
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Old 28th Jun 2020, 9:42 am   #31
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Default Re: Marconi 1400 birthday present

The linearity sleeve always becomes detached from the plastic bit.
It's basically consists of a loop of copper foil sandwiched between two sheets of thick paper formed into a circular tube that slides between the neck of the tube and the scan coils. You will have to loosen off the coils to access the loop which may be stuck to the neck. It usually comes away easily.

It's position is critical. If pushed in too far the width will be reduced together with poor linearity. I would suggest that you recover the paper tube and restick the plastic ring. The dirty mark on the paper will show how far it was originally slid inside the coils.

The adjustment becomes critical the further it is pushed in.

It MUST be fitted parallel with the open slot of the paper tube dead straight.
J.

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Old 28th Jun 2020, 11:46 am   #32
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Default Re: Marconi 1400 birthday present

Thanks Dazzlevision and John .between both of your pictures that all makes perfect sense and explaining it . I will get back to that later.
One other thing I find is now I got the replacment tuner working is on first switch on from cold I get no sound or vision . If I change channel and go back to the original channel it works fine. Maybe the jolt from changing Chanel disturbs a bad connection in side. Andy
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Old 28th Jun 2020, 11:57 am   #33
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Default Re: Marconi 1400 birthday present

Have you cleaned the rotor earthing springs in the tuner? They are thin leaf type contacts which are soldered to the tuner body and earth the moving part of the tuner. You need a heavy duty soldering iron to remove them . Clean off the old grease slightly re-tension the spring and refit.
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Old 29th Jun 2020, 2:21 am   #34
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Default Re: Marconi 1400 birthday present

Thanks Slidertogrid I will investigate. Iím still having problems with the width. I have now carefully pulled out the linearity sleeve. Itís made a slight difference but not that much. Infact I would say itís also shrank the castalisations on the left at the same time as slightly improving the width.. I have pulled the sleeve out about 5/8 of a inch . Is this to much .As in the picture .Any more ideas ? Andy
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Old 29th Jun 2020, 7:31 am   #35
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Default Re: Marconi 1400 birthday present

Can you confirm youíve replaced the boost HT reservoir capacitor, C105 (0.22uF - use a metallised Polypropylene film type) and both of the S-correction capacitors C107 (0.1uF on 625) and C108 (0.3uF on 405). The values of the two S-correction capacitors is critical.

Is the HT supply to the line output stage now correct?
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Old 30th Jun 2020, 1:57 am   #36
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Default Re: Marconi 1400 birthday present

Dazzlevision. I have previously changed those 3 capacitors . I normally check them as I change them . The S correction on 625 was open circuit.
I just double checked again I didnít make any mistake.
Going back to the HT voltage ..
Ht1 reading is about 4 volts over ,again the same with HT2.
But here is possibly the problem. HT3 is 173 volt and it should be 215 volt.
Having said that my manual must be an early one as it shows R135 as 1.5K and as I mentioned earlier mine has a 1.7K section. Maybe I should try reducing it abit and see what happens. Andy
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Old 30th Jun 2020, 9:36 am   #37
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Default Re: Marconi 1400 birthday present

OK, if you are sure that all the critical capacitors have been replaced in the line output stage and you’ve tested and replaced where necessary, all the high value resistors, then I suggest:

1. Is the line drive coupling capacitor C117 47nF OK? If it’s a Hunts, Erie or TCC branded paper dielectric type, it will be suspect.

2. Is R138 2.2k PL504’s g2 feed OK? It’s probably a wirewound, but just in case....

3. Is the line linearity sleeve correctly orientated - the gap in the “paper” cylinder should be the same along its entire length and parallel to the axis of the CRT’s neck.

4. Check for out of spec carbon composition resistors in the line blocking oscillator circuit: R70 39k, R66 4.7k (HT4 dropper). Might be worth trying another 30FL1/2, if you have one.

5. Have you already proved the PL504 and U193/PY801 are OK, by substitution?

I doubt if the value of R135 (1.5k/1.7k) is relevant to the width issue, as HT3 feeds the frame output stage.

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Old 30th Jun 2020, 8:09 pm   #38
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Default Re: Marconi 1400 birthday present

Hi Andy,
I've been following your progress with interest as I have the same set. I bought it from Harpenden BVWS auction some while ago but have not got round to it yet.

I would expect much more width than you are getting, especially at the maximum setting of the width control.

One of my suggestions was going to be to try a different 30FL2 line oscillator and to measure the voltage on it's anode. Also a different PL504 & PY800. Dazzlevision has beaten me too it though!

The other culprit could be the width stabilisation VDR (Z4). These don't usually seem to give much trouble, but I recently had a very similar problem on a KB VC4 with low width and low boost volts. The VDR was the problem. I also found that the value of the scan coil coupling capacitors was extremely critical- a small change in value made a big difference to the width even though the boost volts remained the same.

Have you measured your boost volts? The circuit I'm looking at doesn't show what they should be but that information will be out there somewhere! The boost voltage can be a good indicator of what's going on in the line stage.

Good progress so far!

All the best
Nick
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Old 1st Jul 2020, 2:01 am   #39
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Default Re: Marconi 1400 birthday present

Thank you both for your ideas on what to try next. I have already replaced valve 30FL2.
I have tried replacing Pl 504 and PY800. PY800 made just a very minor improvement hardly noticeable. I will check the resistors and caps mentioned. In one of John Laws articles he mentioned a possible faulty VDR but not a common fault.
I will do the checks when I have time. Thanks again Andy
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Old 1st Jul 2020, 11:20 am   #40
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Default Re: Marconi 1400 birthday present

Quote:
Originally Posted by dazzlevision View Post
OK, if you are sure that all the critical capacitors have been replaced in the line output stage and you’ve tested and replaced where necessary, all the high value resistors, then I suggest:

Check for out of spec carbon composition resistors in the line blocking oscillator circuit: R70 39k.
Note that R70 changes to 33k in later production, "to cure line scan crushing". Worth changing to this value, even if the originally fitted 39k resistor is within spec - unlikely after 50 years!
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