Notifications
Clear all

B&W TV Rediffusion "Guildford" RT 194/19 Dual Standard

Page 9 / 10
 
Doz
 Doz
(@doz)
Noble V-Ratter Registered
Posts: 1329

Epic. I'm amazed the diodes are fast enough.

ReplyQuote
Posted : 08/05/2022 8:33 pm
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

@doz they're used in a voltage doubler circuit in microwave ovens so they're really suited to this. Probably complete overkill being used in a TV tripler but that'll hopefully make it last a long time.

ReplyQuote
Topic starter Posted : 08/05/2022 9:45 pm
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

So, that's every brass-ended resistor in the two main boards replaced along with any of the brown carbon resistors that didn't test ok or looked iffy (particularly ones mounted right above valves) along with the iffy capacitors, which was pretty much all of them except the ceramic ones and the mustard Mullard ones.

20220508 212122

 The Tropical Fish caps were all starting to crumble:

20220507 171156

Any components directly above valves I either laid down flat to the board or in some cases mounted them on the other side of the board.

20220508 215933
ReplyQuote
Topic starter Posted : 08/05/2022 10:03 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4158

The leads of those  “tropical fish” capacitors easily break from the body. 

ReplyQuote
Posted : 09/05/2022 8:15 am
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

@nuvistor yeah, although that's one of the better ones! One dropped off the board leaving the two leads still soldered to the board.

ReplyQuote
Topic starter Posted : 09/05/2022 11:19 am
slidertogrid
(@slidertogrid)
Reputable V-Ratter Registered
Posts: 359

@wayned I think it is an age thing. I found about 20 packs of new ones and about half had cracks in one or both ends, the wire leg would just drop off when touched.

ReplyQuote
Posted : 09/05/2022 10:34 pm
WayneD liked
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

Finally got round to refitting the board that I've just replaced the resistors and capacitors on and...

20220510 205008
20220510 205033

 That's a seriously nice picture! 

There's still a bit of mains ripple as well as a bit of a buzz through the audio, but I haven't touched the HT smoothing capacitors yet.

Have to say this is a very satisfying TV to work on. 

ReplyQuote
Topic starter Posted : 10/05/2022 9:45 pm
Lloyd, PYE625, Nuvistor and 2 people liked
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

Weird problem I had which I hadn't been able to solve was every 5-10 minutes the line hold would go weird and refuse to lock unless I tweaked the vertical height slightly. Adjusting the line hold did nothing.

Someone suggested the PCF80 line oscillator valve could be at fault, which I thought was odd since I replaced it with a new old stock Pinnacle PCF80 whilst I was trying to get the TV initially running. They suggested try a PCF802 in place as they're supposedly a more modern equivalent but the TV didn't like that at all. 

Out of curiosity, I tried the original Mazda PCF80 that came with the TV and suddenly the line lock fault has disappeared! I also have a lot more adjustment available in the line hold control.

20220518 195004

I suppose never assume a valve is good just because it's new old stock? 🤔 

20220518 194013
ReplyQuote
Topic starter Posted : 18/05/2022 8:43 pm
Nuvistor, Lloyd, PYE625 and 1 people liked
PYE625
(@pye625)
Famed V-Ratter Registered
Posts: 4980

The A640 chassis is a nice one and I do like it.

When my set was working, I was really impressed with the results. It has had to be moth-balled for now though.

With care, it show's just how good they can be.

You have achieved fantastic results and I swear that your CRT is improving with use. 👍 

ReplyQuote
Posted : 18/05/2022 9:58 pm
WayneD liked
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4158

@wayned 

There should be a date code on the Pinnacle valve, simple month/year showing when it was supplied to the retailer, not its date of manufacture. They gave a 12 month guarantee from this date unlike Mullard/Mazda which was 3 months from fitting.

The Pinnacle valves were generally very good and had a no quibble replacement policy, no use to you now though. 🙄 

 

ReplyQuote
Posted : 18/05/2022 10:59 pm
WayneD liked
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274
Posted by: @pye625

You have achieved fantastic results and I swear that your CRT is improving with use. 👍 

Your eyes don't deceive you, it's definitely getting better! 

I have to admit, I made a bit of a rookie error with this TV as I didn't test the CRT prior to getting it functional. It was only after I did the tripler conversion that I realised Carol Hersee's face was starting to look a bit like the aliens in the 80s film "Cocoon"

I put my tester on the tube and... the needle didn't even move! After verifying that I'd definitely connected it correctly several times, I got a bit of a sinking feeling. I thought sod it, and cranked up the heaters to around 8 volts and left it for a couple of hours. Tested it again and now it's into the yellow on the meter even at 6.3 volts and when I tried the TV again the picture was a million times clearer. However, the more I use it the more the emissions are coming up, it's just nudging the beginning of the green on the meter.

ReplyQuote
Topic starter Posted : 19/05/2022 11:23 am
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

@nuvistor can't see any date code on the valve. Looks like something has rubbed off.

20220519 175601

 Of course, it's entirely possible that someone swapped it for a duff one and put it back.

20220519 175512

 I don't know if "P557" on the box means anything.

20220518 195004

There's also a "3" moulded into the glass on the bottom.

ReplyQuote
Topic starter Posted : 19/05/2022 6:00 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4158

@wayned 

The date code appears to have rubbed off, the P557 will be a Pinnacle stock number.

For future reference if anyone is interested this is a Pinnacle UCL83 date code Aug 1975.

Frank

0DF33236 9ABD 4AAC 8B2F C6EB97DC22B4
ReplyQuote
Posted : 19/05/2022 9:37 pm
WayneD liked
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

Bit of an odd problem, there's a very slow ripple on the picture which starts off really bad from cold but after 30-45 minutes it starts to improve until eventually it's barely noticable. When I adjust the line hold it does affect the speed of the ripple slightly. 

As I've already been through the dodgy capacitors and resistors I'm wondering if this is a timebase issue? 

ReplyQuote
Topic starter Posted : 28/05/2022 5:48 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4158

Could be an electrolytic smoothing cap slowing reforming after 30 mins or so. 
Using my phone at the moment so can’t check the circuit. 

ReplyQuote
Posted : 28/05/2022 8:10 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4158

Also worth checking any chassis connections in the smoothing and line circuit in case they change when warm.

ReplyQuote
Posted : 28/05/2022 9:36 pm
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

@nuvistor I have replaced the smoothing caps, but I'm going to go through them again as it wouldn't be the first time I've replaced a capacitor only to find the new one is defective. 

Chassis ground connections have been mentioned a couple of times as well now. 

More testing tomorrow.

ReplyQuote
Topic starter Posted : 28/05/2022 10:23 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4158

@wayned 

An heater cathode leak in a valve could cause it but I would have thought it would have got worse with use rather than better.

Still something to keep in mind and one of the easier tests is a replacement valve. 

A leak in a valve base or a more worrying fault is a leak in the PCB around a valve base.

Fingers crossed its a simple fix.

 

 

ReplyQuote
Posted : 29/05/2022 7:59 am
WayneD liked
WayneD
(@wayned)
Reputable V-Ratter Registered
Posts: 274

So.... replaced the PCF80 with a new old stock Tungsram version I've just received and now there's no ripple from cold but if I adjust the horizontal control even slightly the ripple starts again. 🤔 

I'm waiting for some other valves as I'm no longer trusting the new old stock valves I have as I'm starting to suspect the box I have was someone's rejects. Have to say I'm impressed with Tungsram valves, the PL504 I replaced in this set with this one has been brilliant. 

ReplyQuote
Topic starter Posted : 02/06/2022 9:19 pm
PYE625
(@pye625)
Famed V-Ratter Registered
Posts: 4980
Posted by: @nuvistor

..... a leak in the PCB around a valve base.

This is something that is mentioned by LLJ in his article on the chassis. It is something to bear in mind, especially if there are heat related marks around the valve holders of the heavier duty valves. A solution is to drill holes between pins in the pcb, but obviously this is a last resort. You need to be pretty certain that it is indeed the cause of the problem, perhaps a high resistance measurement might give a clue.

There is possibly a rather naughty way to establish if it is in fact AC/half rectified heater voltage causing the ripple problem. If you study the circuit, you will see that a diode 3D9 feeds the heater circuit. If you make arrangements for a switch to be temporarily fitted immediately before or after this diode, you could briefly interrupt the heater supply only.

With the fault clearly displayed on screen, open the switch and see if the ripple immediately goes. You need to be fairly quick to then close the switch to maintain heater supply to avoid damage to the valves, or simply switch off the set proper.

If the ripple remains, it is not heater voltage leaking.

 

ReplyQuote
Posted : 03/06/2022 10:12 pm
WayneD liked
Page 9 / 10