Can’t load from tape when connected to my CRT TV

[Lardo Boffin]

An interesting one. Well, kind of.

I have a small glass screen CRT telly mostly used for testing zeddies prior to refurb. It is very easy to get a picture so therefore easy to see if they work or not.

I am currently refurbing a zeddie that came with a Sinclair RAM pack so rather than fit an internal 16K mod (harder work on an issue three) I decided to send it back out with the RAM pack. I wanted to soak test the RAM pack for a day (have changed the caps) but didn’t want to fit a ZX8-CCB until I was sure about the RAM pack as fitting the 16K mod would be more involved with it fitted.
So I decided to connect it to my glass screen telly and load The Gauntlet, my favourite tester. It has a nice demo mode.
Could I get it to load? Nope. Many attempts failed. Tape works, player works, cable is fine. Tested on a different zeddy connected to a different telly as it is composite modded. Loads fine.
I removed the RAM pack from the zeddy and tried a 1K game (also known working). Nope.
My tape player has a monitor setting so I had that going and noticed a load of noise coming out of the refurb zeddy via the monitor. I assumed at this stage the ULA was dodgy - won’t load and weird noise. My other zeddy (although not my only other zeddy ) made practically no noise.
Back to the poorly zeddy and randomly I switched the glass screen telly off (with the zeddy on) to give up and the noise from the monitor speaker stopped. Switched it back on again and back it came.
I just about managed to get the zeddy tuned in on an LCD monitor and no noise. The tape loaded first time.

So there you go. A whole lot of preamble just to say that the interference (or whatever) from my glass screen telly is bad enough to stop tapes loading on my zeddy.
Go figure.

Edited to reduce confusion.

[1024MAK]

Err, okay, I admit it, I’ve not been in Curry’s for a while now, so am not up-to-date with the latest marketing ‘buzz’ words in TV box shifting, so what is a ‘glass screen telly’?

Only CRT tellies were rather heavy with the glass screeen/CRT tube. And the LCD TVs that I have, have glass displays.

So I’m a bit confused

Mark

[bola_dor]

I can't help much but with glass TV you mean CRT?
Perhaps shielding and ground are not good enough..
If other ZX can load with that TV then or thevZX is more sensitive to interference than the normal or the interference is generated by your new ZX.
What about switching the ULA with one of the others ZX you do have?

[Lardo Boffin]

Yes a CRT telly.

Funny I always assumed that LCD tvs being a bit like a large laptop screen would have some sort of plastic screen not glass. My LCD tvs screens don’t feel like smooth glass but I have never looked into what the screen is made of.

Its the first time I have tried to load from tape connected to the CRT via RF. Will see if other zeddies are affected.

Just thought it was interesting and unexpected that the choice of TV could make the hard enough task of loading zeddies tapes harder!

[1024MAK]

LCD are based on glass. Everything (you may not want to know) about LCDs is here.

CRT displays do produce a strong 15625 Hz signal, this is from the horizontal/line output stage. Young humans can often hear this, as it is within their audio range (alas, I can no longer hear it, so that means I am no longer young ). Some also have a switch mode power supply unit (SMPSU) which may also generate interference and harmonics (possibly in the audio range).

The Zeddy was designed with CRTs in mind for the display (as this was at the time the only practical and affordable display technology), so a CRT telly that generates no more than the normal / typical amount of interference should not affect loading. And the ZX81 circuitry does include some crude input circuitry (R33, R34 and C10), although it’s not designed to filter out interference from a CRT telly, more to provide a load for the tape player, to block DC and to attenuate the signal.

So I can only speculate that your CRT telly either generates more interference than normal/typical, or it has developed a fault. Is this TV a class I (requires an earth connection) or class II (no earth connection required)?

Were you loading (or trying to) with both Ear and Mic leads both connected at the same time?

Mark

[Lardo Boffin]

Just had a look and it is a class 1. It is a TV/DVD combo telly.
I only ever have the EAR plugged in - I think I read somewhere that this was the best way forward.
Also the tape player is connected to a different wall socket to the zeddy and telly is connected to different one to those two.

[Moggy]

I too have an old Alba CRT TV and when I used to tape load I had to have the cassette player at 90deg to the tube otherwise no joy so Marks explanation answers my old puzzle too.

[1024MAK]

It is indeed recommended not to have both the Ear and Mic plugs connected at the same time. This is because some cassette decks have a ‘monitor’ facility (so that when headphones/ an earpiece is being used, the user can monitor the audio that is being recorded).

It is also recommended to have both the computer and the cassette tape deck at least 60cm (2 feet) from the (CRT) TV.

Mark

[avrovulcan]

Good reminder. I had forgotten all about that. This info will come in handy as I'm using an old 240VAC/12V DC camping TV/VCR combo for my retro computers, until I can get all my stuff up and running on RGB/VGA adaptors.

Again, thanks for the reminders.