Pulling a bad tooth out (BBC UHF modulator)

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BadProgram
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Pulling a bad tooth out (BBC UHF modulator)

Post by BadProgram » Thu Mar 22, 2018 10:18 pm

Whiskey wont cure this one, is removing the UHF modulator a matter of desoldering it ? (Model b rev7) or would it require more skill and knowledge. Any background noise my Beeb makes seams to be related to the UHF modulator, i fear somehow the interference has caused the few disk or tape corruptions ive experienced when saving or loading.

thanks.

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1024MAK
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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by 1024MAK » Thu Mar 22, 2018 11:57 pm

You don't even have to desolder it. Just cut the two wires going into it. One is the +5V supply, the other is the video input.

Although note that the output power of a modulator is very low, so it is very unlikely to affect disk drives / disks or tapes.

Mark

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MartinB
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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by MartinB » Fri Mar 23, 2018 12:11 am

Are you sure you’re not hearing the Beeb’s ubiquitous 1MHz bus noise? This is a shushing/buzz that varies with the Beeb’s activity and key presses. It can be cured with the addition of a resistor (no details to hand as I’m in bed, you could search the forum) but like the modulator, it’s highly unlikely (I’d say impossible myself) that this would cause any data recording corruptions. A bit of video with audio might help us to offer a more informed opinion.

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BadProgram
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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by BadProgram » Fri Mar 23, 2018 12:22 am

thanks for the detailed instructions on removing the UHF modulator and particularly for the opinions of UHF noise probably not interfering with disc/tape writes (I'm brushing up on my disc skills not having used the powerful acorn disc system since the early 90s). Ps i reckon its not the 1MHz bus noise i hear as my screen shows interference's in parallel with the noise if using the UHF. i supposed the 1MHz bus noise was the very low hum that alternates frequency depending on the information being used on screen ?.

cheers.
Mark.

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vanekp
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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by vanekp » Fri Mar 23, 2018 6:22 am

May be worth checking your power supply especially the capacitors, if they are faulty it could introduce noise on the +5v and cause all sort of problems.
Peter.

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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by grobda » Fri Mar 23, 2018 3:45 pm

vanekp wrote:May be worth checking your power supply especially the capacitors, if they are faulty it could introduce noise on the +5v and cause all sort of problems.
Peter.
I second this, had an arcade PCB that had a faulty capacitor in the sound amp section and was causing both audio and video interference.

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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by crj » Fri Mar 23, 2018 3:50 pm

1024MAK wrote:You don't even have to desolder it. Just cut the two wires going into it.
Given how hard it would be to get a replacement, it might be prudent to remove the modulator in a way that allows it to be reinstated later?

Also, surely you also have to sever the ground connection?

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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by 1024MAK » Fri Mar 23, 2018 6:12 pm

The ground connection is via the case. Removing the modulator requires a soldering iron with plenty of power and a large chisel tip. This is because the tin case sucks away the heat when you attempt to desolder the metal tabs that hold it in place. It's not a job for the faint hearted.

Electrically, there is no need to disconnect the ground (or 0V) connection. As without the +5V power feed and with the video input disconnected, it can't affect anything.

Mark

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BadProgram
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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by BadProgram » Fri Mar 23, 2018 9:47 pm

Hi, My Beebs power supply was serviced in 2017, the noise levels of the machine are very low and the way the noise introduces itself reminds me of a failing capacitor. weirdly over the last few days its been very silent. I will consider all the fantastic information in these posts before committing to any services myself because of her age and myself only being an amateur electrician. I will certainly upload a video of any issues here before a final commitment thanks very much.

mark.

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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by Bat » Wed Mar 28, 2018 9:51 am

Hi,
Take a look at this...
viewtopic.php?f=3&t=2190&start=60#p198819
It may well be what you're experiencing? It's certainly reduced the noise on my speaker.
Cheers,
Gavin :)

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BadProgram
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Re: Pulling a bad tooth out (BBC UHF modulator)

Post by BadProgram » Fri Apr 27, 2018 8:33 pm

To conclude my BBC B issue and perhaps help anyone else in a similar situation. After consideration on the posts i received and the help currently available for hardware services, ive decided that ill give her the hollywood treatment and spend and extra few quid booking her in with a top surgeon for a service. Modulator replacement and full board inspection. Upon her next calling for it (she's in operation 2-3 hours an night as a catalogue,calculate and study. and i admit i load up exile and its probably addictive). i suggest anyone else in my situation do the same, look online at the quality of the services available, there are some very knowledgeable and talented engineers offering their service.

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