It's a compact set. The 900 chassis is often referred to as the "cool" chassis, designed to use less energy. It features no wasteful "dropper" resistor to obtain the correct voltages, but a mains auto transformer.
Red EHT rectifier tray. This is semi-conductor, and is mounted on top of the very reliable "jelly-pot" line output transformer.
Initial results are encouraging. Very poor frame linearity, and hold. Usually caused by a poor PCL805 or it's cathode decoupling. Not in this case, however! As usual, it was down to a capacitor on the secondary of the frame output transformer. Bob the bodger had previously been at work around the frame stage, and had fitted two replacement resistors (of the wrong value!) and a cap (of the wrong value!) After these were replaced, results on 405 lines were encouraging.
Initial results... poor linearity and frame lock.
UHF 625 operation was not good. Signals are available from my test rack at UHF channel 40, 50 and 60. In addition to signals on 36 and 68 from the house distribution system.
Reception on Ch 36 was OK, if a little grainy. Channel 60 was available strongly, although was extremely touchy to tune, and Channel 68 was good. Where are 40 and 50?
It turns out that the PC88 is the guilty party!
... and 625. After a few minutes some hum starts to disturb the sound and picture.... It's pretty obvious a re-cap of the set will be required...
Quite a few caps are in physically poor condition, or electrically faulty and are replaced, along with the PC88....
The set then functions well, so I re-install the chassis into the cabinet. The set then suffers with intermittent frame collapse (no frame drive), leaving a horizontal line on the centre of the CRT....
After much probing about with an insulated screwdriver, I spot something arcing on the scan coils...... it's a thermistor (or rather was!). It's turned into a blob of something... I don't have a replacement (and I've got precious little chance of getting one), so I shorted it out, restoring operation.
And here's a video of the set working...
Yet again Andy, another highly enjoyable and educational video.
ReplyDeleteThank you for sharing, these are always a great treat!
Andy2.
Hi Andy, Fantastic video. I have one of these sets with picture flicking from line across the screen to full picture again in quick succession. I've had it stuck on a shelf in my bedroom for years. I been trying to get it going again, but can't find suitable capacitors to use as replacements. You had all the old ones laying on the top but I couldn't see what you replaced them with. Would love to know. Thanks. many whippet
ReplyDeletePS My set has the flywheel sync module
+manny whippet Good point... I like this series of caps from Vishay, and the audiophiles seem to rate them... MKT1813 Polyester Cap 220nF 400V 10% RS Stock No.185-4369. I also use a lot of Vishay 10nF ±10% 220 V ac, 400 V dc Through Hole Polyester Film Capacitor RS Stock No.115-231 , which are great caps, but don't look original in most kit, if you're fussy. RS will happily supply anyone, and stuff is usually in stock and they deliver quickly. The numbers here are just guides, most values are available. Don't fuss too much if you can't find 0.05, just use a 0.047. It will work out just fine. Have fun, and get that Fergy fixed!
ReplyDeleteLove the look of the tv i rather like the smaller crt types and this one is a beauty !
ReplyDeleteBrilliant information! I have one of these in good working order and I am looking to sell it. Could you give any idea of the value? I also have a couple of spare valves/resistors and the original power leads...Would anyone on hear be in the market for one?
ReplyDeleteI would try eBay. Everything seems to find it's value on there. I paid £30 for mine. If you do go down the eBay route, don't offer shipping, it'll arrive in bits.
DeleteThere's always www.radios-tv.co.uk You'll need to be a member to sell something, but Chris who owns the site is very helpful.
Delete