CPC 464 Loading issues.

[Buleste]

I've added an external audio input to my CPC 464 and it was working perfectly.


Unfortunately I had to take my 464 apart and in my haste to put it back together I switched the keyboard ribbons around and obviously when I tried to press keys nothing happened.
I put them back in the correct way but ever since then the 464 isn't 'hearing' the input. It's coming through the speaker fine.
I was wondering if my mistake with the keyboard could've mucked something up.

EDIT: I've checked that the relay works, and it does. I've also tried to see if a basic programme can be saved and it can.

[Shaun M. Neary]

I'll hazard a guess...

I was gonna say check the black lead from the tape deck to the board. That could cause you to hear the load through the speaker but not register with the CPC, but if it's saving that's probably not it... unless it's not seated correctly? Maybe try disconnecting it and re-connecting it again?

I *think* this caused an issue for me in the past, but we're going back almost 30 years, so I'm open to correction to those more in the know.

[jpx13]

Hello,

Can you tell us how did you wire your sound input ?

JP

[Buleste]

The Audio is to the DATA IN pin. It was working perfectly before but isn't now.

I've tried a CD/Cassette attached to my PC and it seems that no audio at all is coming in through that.

EDIT: Curiouser and curiouser. Using WinTZX and my PC and everything works properly but nothing else is. I wonder if the LA6324 has gone tits up?

[jpx13]

Hi,

OK, All the Audio IN schematics I've seen are using different input points: One is by wiring directly to the R/W head input on the datacorder PCB (Which I'm using and allows to read, but also to export audio by pressing the REC button), the other is by using another point on the PCB (you can find this in the cpcWiki mods page). With both, it seems to me that the signal is processed through the amp of the datacorder and various resistors before going to the cpc motherboard.

I wonder if by wiring directly to the input it could be hazardous and could damage the 8255 if the level is too high...

What do you mean by "Using WinTZX and my PC and everything works properly but nothing else is" ? Is it working with your input and using a PC as a player ?

JP

[Bryce]

Small correction to jpx13 info: The first section of the tapedeck "amplifier" real is an amplifier (IC302 pins 5,6 and 7), but the second section (IC302 pins 8,9 and 10) is a comparator not an amplifier. This is doing the signal conditioning to make the signal suitable for the 8255 and any external audio signal should be routed through this. It will make the signal suitable for the 8255.
I wouldn't recommend wiring directly to the tapes pickup head, because it is very easy to destroy the heads coil if the current is too high.The safest point to connect an external source (with amplification by the CPC) would be pin 6 of IC302. If your external source has enough amplification of its own, then I'd choose pin 9 of IC302.
If you are using a Datarecorder from some other computer that already does signal conditioning or you are willing to mess around with signal levels for a long time, then connecting directly to the 8255 isn't a problem.

Bryce.

[Buleste]

I've tried the audio in in several places as I'm trying to use my TZXDuino and use motor control via a DIN.

I've tried this one but it didn't seem to work for me.

[attach=2]

I also tried the Direct to tape heads on the wiki page underneath and that didn't work either.

This is the one I discovered eventually that did work until my mishap with the keyboard ribbons

[attach=3]

I've now socketed the LA6324 and ordered a replacement which should fix my issue.

I'll just have to keep using WINTZX to playback the files for now as that seems to be the only way it works at the moment.

[jpx13]

Thanks Bryce for your clear explanations !

Do you think that pin 6 of IC302 will allow to save audio to an external recorder (or computer) or should it be wired to another point (to add a data output) like pin 2 on IC 302 ?

I ask this because the datacorder of my 464 seems to read correctly audio tapes, but saves with really bad quality, and thus is unable to load back what I've saved... Using the wiring on the R/W head, the audio saved to a computer is clear and perfectly loadable if I copy it to a tape with another recorder... Perhaps my R/W head is not performing as it should when saving ?

JP

[Buleste]

Thanks Bryce for your clear explanations !

Do you think that pin 6 of IC302 will allow to save audio to an external recorder (or computer) or should it be wired to another point (to add a data output) like pin 2 on IC 302 ?

I ask this because the datacorder of my 464 seems to read correctly audio tapes, but saves with really bad quality, and thus is unable to load back what I've saved... Using the wiring on the R/W head, the audio saved to a computer is clear and perfectly loadable if I copy it to a tape with another recorder... Perhaps my R/W head is not performing as it should when saving ?

JP

Have you tried adding an on off switch to your wiring so that your modification doesn't interfere with the running of the datacorder in normal mode? e.g. switch the mod off when recording to cassetee?

[jpx13]

Hi,

I Thought doing that, but the record quality was also bad before adding my wiring... In fact, I added the plug because I was unable to save to cassette.

I cleaned twice the head without any improvement.

Thx,

JP

[Bryce]

This is the one I discovered eventually that did work until my mishap with the keyboard ribbons

[attach=3]

I've now socketed the LA6324 and ordered a replacement which should fix my issue.

I'll just have to keep using WINTZX to playback the files for now as that seems to be the only way it works at the moment.

Wow, that's a strange place for it to work, because you are connecting it to the wrong input of the amplifier and it getting amplified relative to the input from the read head?? And probably getting inverted at the same time!

@jpx13: No you definitely won't be able to use pin 6 for recording stuff. If you want to record, you'll need to connect your recorder to pin 1 of IC302. If recording are bad on the internal tapedeck, make sure both the read/write AND erase heads are clean. Improper erasing will also cause bad recordings.

Bryce.

[jpx13]

Thanks Bryce, if I add a record out connector to my CPC, I will do as you said, on pin 1.

For the Erasing head, I cleaned it twice with alcool and a swab (as the R/W head). I even tried to erase the tape with a good yamaha multitrack recorder before saving with the CPC, but the sound is always crappy... Is there a better cleaning method ?



JP

[Bryce]

Not really, that should have done it. Posibbly the record head needs to be demagnetised.

Bryce.

[Buleste]

Wow, that's a strange place for it to work, because you are connecting it to the wrong input of the amplifier and it getting amplified relative to the input from the read head?? And probably getting inverted at the same time!

Bryce.

It may be strange but it works. Connecting to pin 5 on the LA6324 does the trick.

[jpx13]

Hello,

This afternoon, I used some free time to try some different  wirings. I wanted to add an input and an output to my 464 in order to save directly to PC (With audacity) and recover my WAV saved program later. Hereafter are my findings, if it could be of some help...

As I sais previously, I wired a 3,5 Jack directly to the R/W Head solderings on the cassette PCB. As Bryce advised to be carefull because there is a risk to ruin the head, I desoldered my wire and soldered on pin 6 of IC 302 for the incomming data, and on pin 1 for the output to the PC.

After closing the CPC case, and starting it, I tried my 2 new jacks. My first surprise was that the input is not working, I mean I was not able to load a game with my android phone as I did before. I tried to load from a working tape a small BASIC program, and it succeeded, but there was not the sound of the stream of data from the internal speaker... I tried to save to the PC, and this worked without any problem.

As I wasn't able to load anymore, I desoldered the input wire from pin 6 and put it back to R/W head on the PCB. After that, loading was successfull, but there was no sound from the speaker when loading,  not even a beep when hitting DEL on the Keyboard. I was afffraid something got fried, but there was still sound at the headphone output !! 

After scratching my head to no avail, I removed the Output wire soldered to pin 1 of IC 302, and the sound was back when loading and when hitting DEL...

So to conclude, my computer returned to its previous state: only one wire to the R/W head, and I will be carefull with the level I apply to this I/O   

While the case was opened, I wired a reset button, so the time spent was not completely useless 

JP

[Buleste]

LA6324 replaced and back to working beautifully again.