Tussles with a HMV portable (BRC 1591 chassis) Help required!

[yampy187]

Hi everyone!

I picked up a rather grubby HMV 14" black and white set today. From the tip of all places

Would anyone happen to have a scan of a service manual I could have a nosey at? When the set is powered up, only the tube heaters are lit. No sound or HT activity to be seen. All fuses are intact and nothing looks obviously cooked or leaking?

Are their any common stock faults with these particular sets?

The set is in pretty good condition under all the filth aside from the usual crusty plastic bits falling off the Tuner.

Any help would be much appreciated!

Jan

[Boater Sam]

Are you referring to valves as Americanese "Tubes"? If you are, please don't, it will confuse anyone offering help as a TV contains only one tube and that's a big one.

Now, are we to understand that all the valves are glowing but nothing is working?
We can go un from here, hopefully.

[yampy187]

Hi. Thanks for the reply. Sorry I should have said. It's the solid state 1591 chassis. Only the tube heater is lit.

Kind regards. Jan

[Restoration73]

Found this on the forum

[Boater Sam]

Most obvious first, If the tube heater is on, the mains transformer,rectifiers and mains/battery switch must be OK. Fuse, F2 2.5A, check with ohm meter as well as visually
Check voltages around transistors VT21 &VT22

[dazzlevision]

Hello,

As the CRT heater is lit, the low voltage supply regulator must be operational, producing the 11.6V dc stabilised supply for most of the circuitry in the set.

However, check that it is not higher than this, due to (amongst other causes) a faulty "set LT voltage" preset pot. If it is high, fix that, otherwise the CRT heater will be overrun, eventually causing low emission.

The supply to the sound output stage is derived from the unregulated dc supply before the LT regulator, so I am surprised you get no sound at all (not even a crackle when you operate the volume control?), unless the loudspeaker is open circuit or the headphone jack socket is defective.

To check if the line output stage is working, check the +300V dc supply line and the +95V dc supply line for the video output stage (both derived from windings on the LOPT). If these are OK, then you ought to be getting at least a raster, unless the EHT rectifier stick is short circuit., but that would load the LOP stage, causing a low +300V rail voltage.

I'd also check the CRT cathode, grid and first anode voltages. If the first anode volts supply is missing/very low, you are unlikely to see a raster. The cathode volts should vary with operation of the brightness control.

Regards,

Dazzlevision

[yampy187]

Hi Everyone!

Thank you all for the helpful replies.

After a bit of further investigation I do have sound although quite faint. The headphone socket is a bit twitchy.

Transistor Voltages,

VT21
B- 18v
E- 18V
C- 12.2v

VT22
B- 5.1v
E- 4.1v
C-18.4v

Tube Voltages,

Cathode - 0v
Grid - 0V
A1 - 24V

I also have no +300v or +95v at the LOPT


Jan

[KeithsTV]

I posted the service and user manuals in this thread some years ago

https://www.vintage-radio.net/forum/...ad.php?t=35588

Keith

[Nicklyons2]

Check either side of R116, I'll bet it's o/c. It may have gone due to Line Output Transistor (VT26) failure but also check C104, C107, the boost diode W11.

[pastyboy]

I have a set that can yield spares its a 12 in from memory, might be a 14 in white ultra, basically working but cabinet yellowed and cracked so not really worth sorting out...

The lopty / split diode used to fail in the later 1690 portables but seem to think these were very reliable in that area.

[yampy187]

Originally Posted by Nicklyons2

Check either side of R116, I'll bet it's o/c. It may have gone due to Line Output Transistor (VT26) failure but also check C104, C107, the boost diode W11.

W11 is fine. R116 is also fine. C107, C104 have both been changed. Still no luck

Originally Posted by pastyboy

I have a set that can yield spares its a 12 in from memory, might be a 14 in white ultra, basically working but cabinet yellowed and cracked so not really worth sorting out...

Hi Pastyboy. I may well take you up on the offer of spares. The whole main chassis? Postage costs etc met of course

Regards, Jan

[Nicklyons2]

Well if R116 hasn't gone my next supposition is that the Line Output stage isn't drawing any current. IMHO the most likely cause is no line drive; measure the voltages around Transistors 23,24 and 25. Another thing you could check for are dry joints on the LOPT pins.

[yampy187]

Originally Posted by Nicklyons2

Well if R116 hasn't gone my next supposition is that the Line Output stage isn't drawing any current. IMHO the most likely cause is no line drive; measure the voltages around Transistors 23,24 and 25. Another thing you could check for are dry joints on the LOPT pins.

Spot on!!

VT23 was shorted. I replaced that transistor and i now have line drive. also a blank raster and sound. i have also rebuilt the tuner which is now mechanically functional. i cant manage to tune anything in just yet and have no snow on the screen, just widely spaced flyback lines.

Am i right in thinking i should be investigating the video rail next?

Kind regards. Jan

[dazzlevision]

Hello,

You say you have sound but can't tune anything in....? Do you mean you have a good level of "hiss (noise)" from the speaker? If yes, then it may be the video output stage is defective, as with inter carrier sound, the 6MHz sound IF signal is derived after the video detector.

If you have no sound hiss, but the audio output stage is working, then it might be the vision IF stages are defective, or the line gated AGC, or the tuner itself.

[yampy187]

Hello.

I have plenty of 'hiss' as you would have if there was no station tuned in. Even without the tuner connected. Not as loud as it could be due to the speaker coil binding on the magnet. I'm pretty sure this set has spend a fair amount of time outside or in the damp.

Regards,

jan

[Restoration73]

Flyback lines suggest the video o/p VT9 is u/s. You can try injecting video (or even audio
tone) into the base via a 100uF cap to check.

[yampy187]

Hi All.

This is what i have managed to get on the screen.

Jan

[ms660]

Check the voltages on VT9.

Lawrence.

[yampy187]

Originally Posted by Restoration73

Flyback lines suggest the video o/p VT9 is u/s. You can try injecting video (or even audio
tone) into the base via a 100uF cap to check.

Hi.

I fed in video to the base of VT9 from a pattern generator. No change on screen. all i get is the sound of what im guessing is the colour sub-carrier? Beating away. when i switch the generator to monochrome it stops.

Originally Posted by ms660

Check the voltages on VT9.

VT9 Voltages

B- 0.2
E- 0.0
C- 93.6

[ms660]

It appears that there is not enough bias voltage on VT9's base, so far as I can see on the schematic (the one I have is in bits) VT9's bias voltage is derived from the video driver which I think is VT6 so check the voltages on VT6.

Lawrence.