After the recent saga with the 960 set, (it's working great now), I thought back to basics with a chassis I know well.
It arrived from Granada land yesterday afternoon..
It's so far had a new dropper fitted (two sections o/c), a new HT rectifier and heater supply rectifier.
This is the result upto now. Both timebases unlockable with frame cramping.
Naturally replacement valves have made no difference.
So a lot of work still to do.
Looking good Brian. If both line and field sync are weak then maybe check around V6, it's screen feed resistor R45 would be my first stop and it's value is the same as in the 1500 at 47kΩ. For the field cramping and weak lock make sure the heater rectifier is ok (I'm sure you will have checked this already) then check C94/5 and R105 which supply and filter the bias for the stage from the heater supply.
I also have a recently acquired 1400, a 20" Ultra 6658 which I'm itching to make a start with, I'll be watching this one with interest.
John.
Hi John,
Line and frame lock are totally none existent. I agree re R45. I've had this fault before on a 1400.
Yes, I've replaced W10 with a BY126.
Trying new PCL805 and 30FL2s made absolutely no difference of course.
I'll be getting back to the set and check those items shortly.
This seems to be a high mileage set. No signs of previous component replacements though the PL504 and PY801 are old style Mullards and the PCL85 an unbranded PCL85/805 type. The system switch was in the 625-line position when I first took the back off.
Looking forward to hear about your 6658.
Cheers,
Brian.
Also read that for line sync troubles check the reference pulse feed from the LOPT tag E via R56/C48 and C42/C47 to W5. A short in the screened lead between R61 and R89 is another possibility. Loss of field hold, worth checking R113 and R114 as they often change in value. C92 and C87 can do the same.
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Good progress made this morning. Replacing R45 cured the lack of sync yet the line hold will drift for awhile until fully warmed up. I guess a new 30FL1/2 will cure that. The one in the set is the original.
R105 was also replaced as it had doubled in value. C94 and C95 are of the type that doesn't fail often, but have found a couple of suitable replacements.
The mains filter C101 was also replaced with a 500V AC rated component.
Non frame linearity persists but a good improvement nevertheless.
I was able to carry out further assessment on the set. Unfortunately the CRT isn't brilliant. With the set correctly tuned in there's also alignment issues that need looking at.
Pleased with the progress so far though.
Cheers,
Brian
Good work Brian. The line linearity looks a bit suspect, almost certainly one or both S correction capacitors s/c depending on which line standard is affected.
John.
Yes John, you're right. Much work still to do on the set of course.
Replacing the original 30FL1 with a 30FL2 solved the drifting line hold.
The set seems to be working well on 625 lines when tried on that standard but the poor condition of the CRT really showed up with the usual defocusing when the contrast/brightness is advanced.
Images here 405 with the colour bars taken on 625.
Also read that for line sync troubles check the reference pulse feed from the LOPT tag E via R56/C48 and C42/C47 to W5. A short in the screened lead between R61 and R89 is another possibility. Loss of field hold, worth checking R113 and R114 as they often change in value. C92 and C87 can do the same.
Hi Chris,
Yes, that crossed my mind too. I had the same fault on another 1400 years ago that was cured on replacing R45.
It seemed a lot worse on this set though. The original R45 had fallen in value so was replaced with little optimism using a 2W replacement.
Thankfully this completely cured the problem.
I did have thoughts the reference pulse feed from the Lopt could be o/c. Unlikely but always a first time!
Cheers,
Brian
I only experienced a single monochrome jellypot failure in my time that wasn't due to external causes and that was on a 1500 due to the reference winding being o/c. Any that were changed were usually due to people using too much heat or excessive time on the pin when replacing the harmonic tuning capacitor.
John.
Electrical breakdown is rare indeed with Jellypots. Apart from my 960 failure there was a report of a Lopt breakdown in another 960 in a 1970 "Your Problems Solved". Another HMV 2633 funnily enough.
George Wilding once reported a failure in a 1400, (no raster) and there was that Test Case in September/October 1981 where lack of width with high EHT in a 1500 was caused by the Lopt.
As you say these transformers are very easy to ruin through too much soldering iron heat when replacing the disc capacitor. I've been guilty of that myself once.
Extreme care in doing this cannot be over emphasised.
Replacing the scan correction capacitors has improved matters immensely. I noticed the 600pF one had already been replaced, the only sign of previous service work apart from valve replacements.
The width control was found set to maximum. Never a good sign. Set to mid-way the boost voltages are below those specified in the service data. I was pleased to note the occasional cracking from the EHT stick rectifiers had stopped too. Having found an old used 2M pre set I'll fit this as the width control and uprate its feed resistor to 680K.
Unfortunately I'm no further forward with the bottom cramping despite replacing several components. Not a fault I've encountered before on a 1400. Just to make sure a new PCL805 was tried.
The valve heaters look a little too bright for my liking. I'm wondering if the BY126 I fitted could be faulty? Frame lock is solid however.
Using an Avo 8 the voltage applied to the heater circuit will read approximately 2/3rds of the correct value so a 6.3v valve will read about 4v on its heater.
A digital meter may give different results.
Its worth checking if you are all concerned.
Frank
Latest image after replacing the scan correction capacitors.
Dr
If the heaters appear to be too bright then check to see if the jumper between tags 32 & 33 near the width control has been made, this adds R107 in parallel with R106 in the heater chain to allow 220V working.
John.
Hi John and Frank,
I'm sure the heater tag is in the 240V position but will check later. Worth noting this link was deleted in later models.
I'll be very concerned if the heaters do turn out to be over run as the condition of the CRT is already poor. Rectifying the fault, should one exist will reveal it to be worse than expected.
The CRT in the set is a CME1602, the rim banded version of the unprotected CME1601.
Hope to look at the set later and will report back.
Brian
The components I ordered have yet to arrive. As I'll be working solidly over the weekend it'll be next week before I can get back to the set.
The bits and the ever essential Soldamop were waiting for me on getting in from work last night.
Looking forward to getting back to the set on Monday.
Some work done yesterday evening. Unfortunately replacing all the suspect capacitors has failed to cure the bottom cramping so I'll be checking more of the resistors next, not forgetting the boost feed to the height control. The card covering the contrast/hold controls has to be removed to gain access to it.
Two of the Callins nasties were replaced too, still a couple more to do. Not unexpectedly they had leaked some contents at the wire ends.
Need to find a source of 2M2 pre-sets that aren't those plastic types I find have a limited life in elderly valved equipment they were never designed for of course. Just need one to replace the width control.
I had a used 2M one, never a good idea to use ex equipment spares if it can be avoided. Couldn't get the holes through nor align it properly. I ended up ruining it.
Had no choice but to re-fit the original 1M control. I'd already changed the feed resistor to 680K. This resulted in the expected lack of width.
Didn't want to resort to 330K here so I've temporarily soldered in another 680K resistor on the print side. Half of 680K is 340K so that's not far out!
Valve heater volts are around 6V on the 6.3V heater ones using a digital multimeter. Must dig out the analogue one to see if it's the expected 4V readings.
On the credit side the CRT is looking a bit better.
NOTE- the test card is of course misadjusted. It will be set up properly when the bottom cramping is sorted out.
Brian
Hi Brian, i have plenty of NOS 2m2 pre-set pots which will fit. PM me your address and i will pop a couple in the post for you, Malc.
Fantastic Malc. Very many thanks!
Brian
