Improving Timex/Sinclair Tape Loading

[sirmorris]

Have you read the original article PDF? That might hold a clue. Also, it sounds like a silly question - sorry, which lead is which? You're not putting input into the output accidentally?

[Lardo Boffin]

I have actually RTFM’d for a change. It says to test the resistance before inserting batteries which I did ok. It also says you can jumper pins 1 and 11 of the IC to get the LED to glow which it doesn’t. I think I am testing with the correct leads but is definitely worth checking.

The only other thing is that on the parts list it says one of the resistors is 80 or so K but a hand written note says 100. Maybe somebody found the 80 doesn’t work?

[1024MAK]

80k ohms is not a standard E12 or E24 series resistor value, so maybe a documentation error?

Mark

[Lardo Boffin]

Had a quick look and it is 82 not 80 (R8). I guess that is ‘80 or so’. Obviously I was more precise when ordering stuff...

24564E12-2098-46CE-92A9-9F733328E299.jpeg

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There is 100K written next to it.

[1024MAK]

R8 and R7 form part of a potential divider that sets the bias for IC1B.

Apart from a multimeter, what test gear do you have?

Mark

[Lardo Boffin]

Just a logic probe.

[1024MAK]

I've not tried any any of these

http://www.instructables.com/id/Use-You ... illoscope/

https://www.zeitnitz.eu/scope_en

https://makezine.com/projects/sound-card-oscilloscope/

http://homediyelectronics.com/projects/ ... illoscope/

But if you have a suitable PC or laptop, they will allow you to see low audio frequency waveforms.

Mark

[daybyter]

http://www.stm32duino.com/viewtopic.php?t=107

The hantek 6022be /bl scopes are also an option.

I think one of those salae clones + sigrok might also be better than your probe:

https://m.ebay.com/itm/24MHz-8CH-USB-Lo ... SwPCVYBD2b

https://m.youtube.com/watch?v=z8Tdz7eQ8n4

[1024MAK]

I've checked the photos of the PCB and all the resistors look correct. I can't check the capacitors, as I can't see all the values. The 1N4148 diode is correct. I can't tell which way round the LED is connected. The markings on the chip are also not readable.

So:-

Testing the LED
===============
Remove both cells (batteries) from their holder.
Connect the positive terminal of a 3V or a 9V battery to a resistor (see below for the value). Then connect the resistor to one of the LED connections. Connect the other LED leg to the battery negative connection. If the LED lights, mark the LED leg connected to the battery negative with a black marker pen (or mark that side of the LED body).
If the LED does not light, try the other polarity.
If the LED does not light at all, disconnect it from the PCB and try again.

Once you have confirmed that the LED is working and are happy with the polarity, ensure that the LED leg marked with the black marker pen is the leg that is wired to the solder pad / track that goes to IC1 pin 14.

For a 3V battery, use a 100 ohm resistor.
For a 9V battery, use a resistor between 330 ohms and 1k ohms.

On the track side, the PCB tracks all look to be laid out compared to the schematic.

Just for my sanity (I know you have already said that you have done this), can you do the checks and tests as per this picture:

Suggested tests on PCB 20180203.jpeg

Suggested tests on PCB

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Mark

[Lardo Boffin]

Thanks Mark. I will try all that tonight when I am back with the stuff.

The IC is http://cpc.farnell.com/texas-instrument ... st=Sc13781

As you look down on the board on its top side with the cables at the top the ‘flat’ of the LED is to the left.

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