[Sticky] 1974 HMV 2726 Coloumaster; Thorn 4000

Key points for you to check. VT452 emitter with a scope for anything coming through the front end when you press any button, even though the hand unit may be a bit off frequency. If you have any other Thorn simple two button remote you can use that also.

If the front end is active stick your logic probe on IC552A pin6 and listen for a pulse train here. If all is good align the remote for 44.4KHz with the saturation down button, no extra capacitance switched in.

IC559 pin10 when the remote is accurately set up will be your channel step pulse. This is processed by VT554/5/7 before being passed to the touch tune IC on the front panel.

IC561 pins 4,5,6 there should be a pulse whose mark/space ratio should change when you change the analogue levels up and down on the remote, pin4 saturation, pin5 brightness, pin6 contrast. Have fun.

And we're in.

I'm looking at all that and thinking "...and then came the SAA5010".

@cathovisor That was later, next came the ITT SAA1024/5 combo, This could be ultrasonic or IR but Thorn only used it as the former. Being PCM (or was it PPM?) it solved the jangling keys and chirping Budgie problem overnight.

Posted by: @jayceebee

If you have any other Thorn simple two button remote you can use that also

I do, I have two 9000 remote units, I did try them on the HMV, but they also did nothing. First things first, I'll follow your previous advice and remove the chips one by one and clean the pins.

Posted by: @jayceebee

next came the ITT SAA1024/5 combo, This could be ultrasonic or IR but Thorn only used it as the former

Would that be this remote for that receiver? As used on the 9904, another set on my hunt list.

No, that's IR using an SAA5000 in the RCU and SAA5010 in the set. With the ITT chip and ultrasonic you could hear the PCM, a rather pleasing tone and different for each button somewhat analogous to touch tone.

ITT chip used also in Thorn's first Teletext set with TiFAX decoder.

My first Teletext set was a Pye 26" G11 in a cabinet with a tambour door and ultrasonic remote control.

That 9904 remote reminds me of the plug-in ITT remote. 

Hooked up the scope and checked for the pulse waveform on VT552. Pushed remote control buttons, nothing. Tried another remote, same, nothing.

Then checked the rails, and I'm missing the 5V supply.

The 150V rail is down 20V, but that is sort of within the 15% tolerance.

Certainly, I needed to find out where my 5V rail had gone. This is supplied via a 7805 regulator IC551. I cannot find this anywhere on the board, and it's not even listed in the parts list of the US receiver. WTF! This was never going to work with the 5V supply missing, so is this somewhere else?

Also the manual refers to the unit being PC

Noting the numbers 111 - 113 on the circuit makes me think it's off-board... and someone has pinched it for a project! Are C552 and C553 present?

The manual says IC551 is part of "Basic Assembly 01M4-070-999"

The 5v regulator is the TO3 device on the metal work. I would be very surprised if it was faulty though. 

IC551 is mounted on the remote metal work in top left hand corner and is listed on last page of part 4 of manual under basic assembley. (remote section). When you've got remote out of the set on your bench I don't think you can see it as it apears to be pointing away from you. 

Posted by: @jayceebee

I would be very surprised if it was faulty though. 

I've certainly had only millivolts on tag 110.

What's on tag 112, the input to the 7805?

There is the possibility the output's in foldback limiting due to, say, a shorted tant?

4.7V

So few things to consider here. No 5v output due to a short? Measure the output pin resistance to deck, feed in 5V from an external PSU but remove the output connection from IC551. W555 faulty giving only 4.5v in is very possible, it was notorious back in the day but usually for intermittent dead set on the later board with a relay for standby switching. 7805 regulator? Never had one go but if it is faulty a TO-220 one with some mounting changes will be fine. Mains TX 11v winding? Again, never had one fail. 

Mains TX feels HOT but I've nothing to gauge that upon, does it run hot anyway, how hot is hot?

Testing at 110, short to ground on the 5V rail.

Posted by: @crustytv

Testing at 110, short to ground on the 5V rail.

You mean 111, don't you?

I was going to say, lift the connection there and test again.

If the regulator's dead (unlikely, but) the LM309K comes in a TO-3 package.

110 and 111 are both 5V rail connections