Original List Price : £175.00 ( 1975 Argos catalogue)
CRT: A47 343X
Never worked on one of these before, in fact the only colour PYE I’ve worked on was a PYE CT203/1 with a hybrid 697 chassis. That was 9 years ago, it’ll make a change from my usual excursions through Thorns’ product catalogue
For the most part it seems to be in reasonable condition. I was shocked to see on the chroma panel a similar thick film unit for the RGB, as used on the 3000 video module. However unlike the 3000 thick film unit of which I have many, the PYE unit 428A/F does not consist of 3 x 11K/56K, it has 3 x 27K/4.7K. I hope it’s OK as unlike the 3000 the PYE chroma board does not have through any hole provision to revert to discrete components.
On the line/field timebase and PSU panel, there’s also a creative lash-up for R531 consisting of 3 series resistors. As I say, overall it looks to be in fairly good condition.
I’m not throwing caution to the wind so no hairy arsed shoving it onto the mains. First I’m going to service the PSU, remove and if possible reform the reservoir caps 535/536 600uF/250uf. Remove and replace the green grenade C501 which is across the line. And replace another green grenade C656, the flyback tuning cap. Oh, and replace the series resistor lash-up. I’ll likely check the line output transistor which is a BU205. I’ve already tested the CRT, and it’s a cracker. So no time wasted in doing the preparatory work.
The 717 chassis is identical to the 715, it’s just cabinet presentation that differs.
The Circuit Boards From The Brochure
This Sets Boards
The boards once cleaned reveal they are in remarkable condition. The only work I can see that’s been carried out is on the Chroma panel, unsurprisingly the thick film unit. I wonder if this is a low hour set, and if so why? The CRT tested VERY good, am I going to find its low hour due to some obscure fault, I always seem to attract the sets with problems.
Mentioned many times before, but worth going over for anyone new looking in. Some may bother with this, some may not, each to their own. I always reform the main reservoir caps, I don’t like brute forcing them, especially if they’re faulty.
The combined multi-can reservoir caps 535/536 600uF/250uf have been removed and is currently reforming. This allows me to supply rated voltage from 0-500 if required in controlled steps. The neon indicator is struck all the time there is leakage, when it extinguishes, leakage has ceased, you can then move onto the next voltage step all the way up to max rated +10%. I connect two meters so I can monitor current and voltage attained. Good caps reform very quickly, some take a few hours and some fail, resulting in replacement. This one is taking its time.
First section, before and after reform
Second section, after reforming
Next, the two green grenades. C501 a 330n 1000VDC across the line, it’ll be replaced with an X2 .15uF 275VAC. The other C656 a 2n7 1500VDC will be replaced with a 2n7 film 1600VDC.
Mon 19th July Update
Reinstalled the newly reformed C535/C536. Replaced the across the line cap, flyback tuning and the lash-up for R531, of which I shall say no more!
Below the 3 x 150K bodge for R531 (470K).
Can we please stop with the bollocks that this was a factory fit! I’ve spoken to an ex TV engineer of old who serviced these TVs on a daily basis, and has many versions of this chassis in his collection. He confirmed R531 was a single 470K. Any further comments posted will be like the last, deleted.
There that’s neater! I also uprated it to a 1W
I had the meter hooked on F541 to chassis, to monitor H.T. which should be 155V
Powered up, nothing!
F526 (1.6A) fuse blown.
Possible causes now need investigation, these are as follows:-
- Zener diode D518 o/c
- o/c junction in T516
- C521 o/c or has decreased in capacitance
- R515 incorrectly adjusted
So after finding none of the above faulty, I just replaced it and then found I had no AC into the board. This was traced to an o/c section of cable from the switch output to timebase/PSU. Repaired the cable now I had A/C into the board, F526 was still OK, but still no life. I then noticed no CRT heaters, checked CRT and it was OK, checked Socket ‘D’ pins 1/3 that was OK so fault is for sure on the timebase. I have AC into the bridge and 322V DC out but the 155V rail only gets to 58V then drops rapidly down to mV. No CRT heaters because that’s derived from the supply DOH! Just trying to get my head around how it’s all supposed to be working, as I’ve not serviced this chassis before. I got really thrown by the BR101 (even though I do have some in stock), not seen one of these before a silicon controlled PNPN switch, configured as a DIAC. I had no idea what that was either until I googled about 10 mins ago. No idea how to test these either, don’t even know if it’s faulty, but it might be or the BT106, though that tested OK in circuit as did the zener and the BC147. Will tackle all this tomorrow.
I think I’m going to get the scope out and see what that state of play is with the BT106 Thyristor, the BR101 PNPN switch and the BC147 transistor.
Looks like the Line output transistor may be responsible for pulling the supply down, the BT106 is OK
Managed to get into the workshop before it gets like a sauna. Replaced the BU205, and as a precaution, replaced the BT106 thyristor and BR101 DIAC. Still no change. New BU205 s/c on B-E so something killed the Line output transistor straight away. Suspect the LOPT.
Well, as a precaution, I removed the LOPT, and it tested OK. Upon further investigation, the BU205 is also OK, turns out there is a short somewhere in the cct that is shorting B/E. Just a matter of finding it now.
Meter across the Base & Emitter connections, reveals a short somewhere further back in the cct
Also, it’s not due to a false reading through Line drive TX, I removed that and the LOPT is out but the short remains.
This has to be a Red Herring!
I Individually removed and checked the surrounding components, all were OK, so put back in, but the short persisted. I’ve just removed them all, now the short is gone.
I suspect I’m just wrong, but I thought reading 27R was not right. What makes me believe I’m wrong is I put R652 back and the 27R reading was back and guess what R652 is 27R. Therefore, I’ve been chasing a bogus short. Hey-ho a twonking I will go.
I’ve put everything back, but replaced the Mullard tropical, as they were quite baked. So to recap, the BU205 has been replaced, along with the Thyristor and DIAC. Disconnected the tripler, powered on and the 155V rail only makes 59V before plummeting. See short vid.
So after all this, I’m still no further discovering what is pulling down the 155V rail.
As Dr Zachary Smith would often say…. “Oh the Pain, the Pain”…
After replacing everything that looked baked in the PSU, I’m still no further, so out with the scope. This reveals the BT106 is totally stalled.
Not sure why the waveform at F526 has that horrible kink in it. I suspect the poor waveform from the anode of the Thyristor is likely due to it not being driven. Why is another matter entirely, and I’ll keep on plugging away.
It’s alive, but the doubler died. The fault was the 15K across the anodes of the DIAC and Thyristor, gone high.
A new 5-wire PYE Doubler arrived, and fitted, however this was also faulty. It only managed to get to 15kV before failing. Before you all start screaming that there is a fault with the TV that is killing the doublers, let me put your minds at rest.
I have in stock two 3-wire low focus voltage PYE CT200 doublers, so I decided to connect one of these. The theory being, if the TV is fine and the 5-wire doublers were just faulty, the 3-wire doubler will produce 20kV and I will have an unfocussed raster. If the TV is killing doublers then it will kill the 3-wire doubler.
Before doing this, I checked the focus unit on the base of the CRT with a Meggar for leakage, it was perfectly OK. I then connected up the 3-wire doubler and powered up. Low and behold I had 20kV and an unfocussed raster, and it remained stable for ages. Nothing wrong wit the TV, just had the misfortune to have two bad 5-wire doublers.
Photo below of PYE TV running with the 3-wire doubler. Now all I have to do is figure out how I provide 5kV of focus voltage.
Not that you can as it won’t photo too well, this is TCF rolling
It worked, I have focus, but there are many other issues to sort, but to my amazement, I have colour!
I think I have some tuner/IF issues which is not surprising as the IF panel seems to have suffered from poor storage, the tuner can is very rusty, and I suspect the whole board needs a good service.
THE END Or is it………….
Update, another 5-wire doubler has been sourced. Although stated as “New old Stock”, I believe it’s a pull, as evidenced by dirt and grime on the final anode lead. Still nothing to lose.
Installed, and this one is holding up, Ssshhhhh don’t want to jinx it!
As you can see still presenting a possible IF fault.
Time to remove the IF and reflow the entire board as it seems to have suffered from moisture at some point and the Tuner can is totally rusty. Though inside it seems, OK, note I said seems.
After reflowing as you might have already guessed, it made no difference. Next I read the excellent article from 1979 by Mike Phelan. Now this then exposed a huge discrepancy with my board. The mains source of problems on the old IF panel was the amplifier module next to the tuner. This was double-sided print, had printed coils, the rivets linking the sides were always a problem and the caps equally not connected that well. The advice being to spend a great deal of time fixing and reworking the amp module.
Imagine my total surprise when I find the module is nothing like the one described, nor does it match what I have in the service manual. Upon further investigation and input from Tas on our Facebook group we discover this board was the LEDCO upgrade that was offered, it uses SAWF!!! remarkable for such an early sets as I thought SAWF came much later.
Anyway, the board in the module looks brand new, with very few parts, I’m not expecting this to be the source of my problem.
I thought I might as well change the NSF tuner can, as I said it was very rusty and its a quick win to replace if its faulty
Well, as you all probably expected this made no difference, but at least it is eliminated as a possible cause. Now its back to the drawing board to track down the cause of the poor signal. I’m wondering if I have multiple faults. If I tune off signal the picture goes black and white (well green as no greyscal done yet) but the definition is greatly improved. If I tune back on signal the colour comes in, but the picture then looks like you see in the photo below.
Interesting that removing colour, the grainy signal appears to clear up. In an attempt to do a quick N dirty grey-scale, I also find the A1’s and RGB gain pots are pretty much seized, all need replacing. There’s a lot more in need of attention and is likely a combination of other problems not helping this, brightness, contrast and colour operation is horrid, crushing the signal. The thick film on the decoder is a top candidate as well, as these are notoriously awful.
Well, I’m yet to see it used in anger, this is the first time it’s been up long enough without eating doublers and loosing sync for me to see a picture. First impressions with just the test-card, it gives a good account of itself. The funny thing is I just did a quick and dirty grey-scale. No attempt at convergence, which you can see is very good. Glad it didn’t need tweaking, as many of the pots are frozen solid. Perhaps that’s why the convergence is good, they are fused so cannot be twiddled.
As for the cct, it’s been an eye-opener and I have to wonder how Thorn always gets bashed when the likes of this PYE far worse. I feel rather thankful that my IF amp module was not the original as, the double-sided board with its printed coils, poor rivets linking the layers and awfully soldered caps, sounded like a total nightmare. Rather than appalled I was totally confused, thinking I must have read it wrong finding the Beam-limiter shared the 12V supply,
I’ve not done a thing to the decoder, it’s running with all its original caps, including the green elctros. Of all the boards designed for the PYE, this looks the best and at a quick glance you could think it was a 3K.
The modular layout is OK, with reasonable access to all boards, but not like a Thorn. If had to choose, a budget colour TV 8K or CT200, Thorn would win every time. Even the Thorn cabinets have nice styling and quality.
I do think of all the Chelsea’s, this final one is probably the nicest looking one. Time to move on to another set.