Zx81plus38 rev1.10 video issues

[ghhann]

Any recommendations for a new tape recorder to use with my zx81plus38 rev 1.10 board?

I saw a few on Amazon $35 dollars or less just looking for any guidance and/or recommendations


All my best

Glenn

[TMAOne]

I can't speak to the ZX81plus38 specifically, but would advise caution with "new" cassette recorders from Amazon and friends. They tend to have newer features like stereo pickup and transfer to SD card or a USB thumbdrive.

Nothing wrong with that of course, but at the same time they've eliminated vintage essentials like a 3.5mm MIC input in favor of a built-in condenser mic. The 3.5mm output is likely also stereo, which can cause trouble without using an adapter, depending on how your particular jack nestles into the pickups.

In short, be careful.

Garage sales, flea markets, and thrift stores are perhaps still the best option. Good luck.

[ghhann]

Thanks for your input!

So I may have found a reason for my tape loading issues. I ordered chips off eBay and instead of getting the last version of some of the 74 logic chips I received all hc versions

Because the stamp was so faded I did not realize. Especially in the pixel shift chips

I ordered new ls versions from mouser that should be in by the end of the week. Ironically loading tapes is the only issue The system ran 3 days straight burn in running a scroll print add 1 loop back program without any issues.

Also the joystick port worked flawlessly as well.

Best to everyone and keep you posted

Glenn

[ghhann]

Quick question

I’m at a point where I can get a load operation completed but it’s full of garbage statements

I’m getting an electrical hum noise on the recording and validated by sending a save wave to tapeutils and analyze as garbage

During a preliminary investigation when looking at the extended bom for 1.10 it looks like the 220 ohm resister is reading as a 200 ohm resister on the farnell Newark website as 200 ohm

Can someone please validate which resister is the correct one ?

Best

[1024MAK]

If you mean R80, it should be 220Ω, Farnell order code 9341528

However, this is not likely to be the cause of your issues. A 200Ω is only 10% lower in value than a 220Ω resistor and often circuitry will still work okay. In this case, a slightly different value for R80 just means that the cassette tape input voltage / volume level may need to be slightly different. R80 sets the negative feedback in the audio amplifier formed by Q9 transistor. A lower value of R80 means there will be slightly less negative feedback meaning slightly more overall gain.

You mention a hum noise. Are all the 0V/GND/screen/shield connections for the cassette tape cables, plugs and sockets okay?

The output from the ZX81+38 cassette output (ZX81 Mic) socket is a very low voltage level. Any bad to poor connections may result in electrical noise / interference that is picked up (from nearby devices) drowning out the wanted signal.

Mark

[ghhann]

Just wanted to close this issue.

Found 2 faults after I put together a 3rd board

1. When using the the tzxduino I was using a 9volt power adapter that’s where the noise was generated and saw it on the scope. After I powered it through the usb connector of the nano unit it loaded files without any errors

2. I was using the original timex Sinclair cables that came with my old ts1000. Once I replaced them with a mono cable from Amazon. It also worked

Lastly on u6 the eight pin was bent. I do not please that’s was a pin that was used so not sure if it’s an issue or not

Thanks to everyone with great suggestions