TC 2048 sound input problem

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johnyept
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Joined: Wed Jul 12, 2017 11:46 pm

TC 2048 sound input problem

Post by johnyept » Thu Jul 13, 2017 12:46 am

I lost my Timex Computer 2068 when I moved to my new house about a decade ago, although I still had the transformer, tape recorder and tapes. So this week I decided to buy a Timex Computer 2048 for nostalgia.

The problem with the TC 2048 is that it doesn't load games. This symptom was confirmed by the seller before the purchase. I turn it on, type LOAD "", press play on the recorder and no blue/red borders appear, it just stays white. It's not a color problem because the TC2048 is connected to the TV with a composite cable (it has a "monitor" connection) and I can see them with the COLOR 2 and COLOR 5 commands. I can also hear the tape recorder sound exiting from the internal speaker. Well I could, until I opened the TC2048 and accidentally disconnected one of the wires connected to the internal speaker.

So, the sound seems to be passing through the jack connection, but not getting to where it should be. Is this a problem with a known solution?

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1024MAK
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Re: TC 2048 sound input problem

Post by 1024MAK » Thu Jul 13, 2017 2:06 am

It's the custom logic chip that "receives" the input from the Ear socket.
When "LOADing" don't have the "Mic" lead connected. As with some tape decks this can cause an audio feedback path :(.
Turn the volume on the tape deck to somewhere between 3/4 and maximum. Remember, the audio signal from the tape deck has to be detected by a 5V logic chip that may consider voltages below 2V to be logic zero (this is an approximation, as we don't actually know the specs of the custom logic chip).

Mark

gozzo
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Re: TC 2048 sound input problem

Post by gozzo » Thu Jul 13, 2017 3:50 am

its usually when saving you dont want to have both leads connected? never known of a cassette recorder to take input on its mic socket when playing, but some certainly feed the mic input back out the ear socket when recording..??

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1024MAK
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Re: TC 2048 sound input problem

Post by 1024MAK » Thu Jul 13, 2017 9:31 am

gozzo wrote:
Thu Jul 13, 2017 3:50 am
its usually when saving you dont want to have both leads connected? never known of a cassette recorder to take input on its mic socket when playing, but some certainly feed the mic input back out the ear socket when recording..??
Yep, that's the main reason, but if you do have loading problems, it's something that is easy to do just in case.

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johnyept
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Re: TC 2048 sound input problem

Post by johnyept » Thu Jul 13, 2017 9:37 am

1024MAK wrote:
Thu Jul 13, 2017 2:06 am
It's the custom logic chip that "receives" the input from the Ear socket.
When "LOADing" don't have the "Mic" lead connected. As with some tape decks this can cause an audio feedback path :(.
Turn the volume on the tape deck to somewhere between 3/4 and maximum. Remember, the audio signal from the tape deck has to be detected by a 5V logic chip that may consider voltages below 2V to be logic zero (this is an approximation, as we don't actually know the specs of the custom logic chip).

Mark
I don't have the original "dual" cable, I'm using a custom cable I made from spare parts so I'm only connecting one jack. Another problem is that I'm a complete newbie when it comes to electronics: I have a soldering iron, a multimeter, and that's it.

However I did notice that a capacitor has been replaced, the one on the far right just below the power switch, the new one says 100uf 40v. I don't have a picture from my motherboard, but it's very similar to the one below, except mine doesn't have the 2nd and 4th chip from that group of 4 chips in the bottom right.
Image

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