I've got a blue AWA P1 portable television that got scrapped ages ago, since there are no transmissions for it to pick up, and therefore useless.

The telescopic aerials were sent to a forum member, and the valves removed. After that it sat on the garage floor for several years, gathering dust and cobwebs.

I've decided to try to get it going again, so I can test more valves. Perhaps I'll add a 75 ohm socket so an old computer could be plugged in, but that's undecided at this stage.

I opened it, found how to unhinge the chassis, and it's clean inside. The original fuses are still there. With no valves in, I switched on, the picture tube heater lit up, then I turned it off, to let the electros reform.

Next I have to find the valves, since they've been dispersed into the main collection, and try again.

So, valves have been added. Turning on gives sound, and with a random wire distorted FM stations can be heard, so I think that part works.

But, there's no picture - just a black screen. The 6BM8 started showing signs of distress, so I discovered a blue wire had become unplugged, and putting that in made the 6BM8 happy. There's also a nearby terminal for a red wire, but I couldn't find a loose red wire.

Still no picture. The grid of the 6CM5 is glowing orange, so maybe no drive? I don't know, I'm out of my depth now. I'm not touching any adjustments, after all the thing worked before. Maybe it's time to use the oscilloscope?

Any suggestions?

Yes it sounds like you have no drive. Look for -30 or so volts on pin 5 of the 6CM5. If you have less than this, but still negative, see the end of this post.

OK, no drive?

Start by looking for 160 volts on R423 (red wire) in the power supply. The 680 ohm might be O/C.

If that's OK, and given that you have V401, a 12AU7, in place, check voltages around it.

Pins 3 and 8 and the 2.2k resistor, should measure 5 to 7 volts. If it's higher than this, suspect an O/C C408, a 680 pF styro cap.
This must be replaced with a styro, dipped mica or NPO ceramic. The hor osc will drift with temperature if the wrong cap is used.

R406, a 68k resistor should also be checked.

Of course, the 12AU7 itself might be dead.

Once you get it running, set the Width to get 420 volts at the junction of the two .047 caps, C414 and C415.

If either of there caps is white and marked "Hi Qual 100" replace it. These are paper caps and like all paper caps they fail. A S/C cap will cause the 6CM5 to red-plate.

The line output transformer will drip wax but a failure of this MSP part is almost unheard of. It will be OK.

Your analogue TV is not useless!
Great for watching old movies and TV shows.

Build my kit:
https://www.siliconchip.com.au/Issue/2018/March/Analog+AudioVideo+Modulator+for+Vintage+TV+sets

Here is a link to a post about it on the US vintage site that I made while I was developing it. There is a schematic there.

https://antiqueradios.com/forums/viewtopic.php?f=3&t=332446&p=2787089&hilit=Playing+DVDs+on+old+TVs+a+solution#p2787089

I couldn't find a 680 ohm resistor in the power supply, even though it's in the schematic, so I measured the voltages on the 2 electros, which were correct.

Next, the grid bias on the 6CM5 was zero, but bouncing around a little bit.

When I started measuring the voltages on the 12AU7, it came good - I suspect a dry joint at pin 8, so I'm warming up the soldering iron now. The only problem is that the very bottom about 5cm of the screen is black. Should I try another 6BM8 ?

More likely to be O/C cathode bypass electro on the 6BM8 causing "up from the bottom"
JJ

Just got back.

The circuit board has dark patches around all the valve sockets, seems it doesn't like the heat much.

I tried a couple more 6BM8's and the 2nd replacement worked. (There's no cathode electro in this design).

A cache of 11x 6BW7 was found so they were all tested in the 6EH7 socket, all worked.

Then the chassis was put back together. One of those little hex-head screws fell into the works somewhere and jammed, shaking wouldn't get it out, so I left it. The whole setup is rather flimsy, but once I got it together I tested it again and it still works.

Last thing was to clean the case and the front. I've left it to dry until the morning then I can put the blue case on, and the job will be complete.

A bag of all kinds of line-output valves was found, I thought they had been lost ages ago.

Thanks Ian for the help and Johnny for the suggestion.

Well, this story isn't over just yet. Turned it on this morning, and black screen. However just by touching the 12AU7 cathode with the meter probe is enough to make it start up. The 2.2k resistor was slightly high so I replaced it, and it worked. But then I came back 10 minutes later and it was black again.

My playtime is up for this week, so it will have to wait until next Sunday night.

What you are getting is a classic symptom of an intermittent O/C 680 pf. It's a fairly common fault.

Even more common in Kriesler models 79-16 to 79-25.

Kriesler had some special caps made (Extended Foil) to overcome this issue.

Thanks, I will report back on Sunday night, assuming I have the appropriate spare part.

I owned a P1 back in the day. It was a great performer for the price.

As I recall, they cost about $10 more than the GE compactron-based portable. But SO much better!

The TV repair firm I worked for in the early 80's had a fleet of P1's which we would leave at customers' homes as loan sets when we took their CTV's away for repair.

They would endure lots of punishment in the forms of hard knocks etc. but withstood most of the misuse and abuse. Valve driven bricks.
I often wonder if they were built to military specs???

AWV, AWA's valve making division, started making several valve types that were previously only made here by Philips for use in the P1.

6EH7
6EJ7
6BM8
6CM5
and, I think, the 6HG8 used in the tuner.

The 6EH7 and 6EJ7 were high performance frame grid pentodes that made a 2 stage vision IF viable.

No not mil spec. One of the reasons it was so reliable is it used "big set parts" and everything was under-run to reduce heat and because of the small CRT. It also had a very compact C core mains transformer, no massive heat generating dropper resistors.

It was also the first AWA design to use a stabilised horizontal output stage, a very Philips concept up until then.
And the first AWA TV to use a printed circuit board.
I think it might also have been the first use of AWA's turret tuner, (previous designs used incremental switches). The coils were wound directly onto the "biscuits" and it used gear-headed tuning slugs for memory fine tuning.

Overall, a very well-thought-out design for the time. It was such a successful chassis that it was adapted to larger portables.