Really nice circuit! If only the original Spectrums used Schmitt triggering for their tape loading; it would certainly have prevented many a headache. And the quality of your work is astounding as always. I've seen far too many ugly hacks, and your attention to detail is refreshing.
I always enjoy these videos, I don't understand most of the complicated bits being only a humble electrical contractor. I can see though that you take enormous pride in the quality of work which is always nice to see. Anyway I have started to cut my teeth on minor electronic products as a bit of a hobby including the +3 sound fix and building small boards for composite video on my Atari 2600jr and my Phillips Videopac. Luckily even though I don't understand what is happening I can follow the circuit diagrams. Thank you for these videos they are very inspiring. :)
Love your videos, really helped me sort out my +2. Always had trouble loading cassette tapes, so having a go at the mod in this video. Just a few small alterations in mine, i.e. I removed R47 and used the top as output for internal cassette and bottom as input for new circuit. I added the removed 680ohm resistor to the output of the new circuit board.
Fantastic video! Enjoyed watching with detailed instructions, wealth of knowledge and step by step instructions! Great that you used multiple angles for video recording! Superb editing and videos, keep them coming! :)
Hi, as you know from my other comments I'm having trouble connecting an external audio source to my +2b, I thought using a 1uf cap connected to the negative terminal of C200/(C41) would route the Audio exactly as the original schematic, but I am getting no sound in, if I omit the capacitor and connect my line in straight to the negative terminal of C200 it works no problem, now I am a complete novice at electronics and I thought I heard the word coupling capacitor somewhere so I had to look up what one did, I don't want to cause more future damage by omitting the cap, from what I read a coupling cap lets ac through and blocks dc which makes sense to me so far as audio should be AC, next I looked up the value of the cap to use for audio and it turns out there are different values for different frequency's, now call me crazy but wouldn't a digital source (cd player/mp3/sound card etc) have a different frequency to an analogue source (old tape players) so now I am wondering if I know my mp3/wav is recorded at 44.1khz would this be radically different from the intended analogue tape source and if so would a rough guess at a 44nf cap work? or 0,05uf, it's the only thing that would make sense to me or have I got that totally wrong, sorry for such a noob question, but as my electronics skills are basic I can only guess. Regards, Chris.
A detailed guide would be great,i think i would like one of these but first need to fix the rf sound i mentioned, after checking from your advice the rod was crushed but when touched brought the sound back briefly
I assume you mean the core of inductor L5. As I noted they are rather delicate. If it is smashed to bits you're going to have to replace the inductor or perhaps you'll be able to find a suitable replacement core. You'll probably have to remove the inductor from the PCB to get the damaged core out. However, if just the top portion of the core is damaged so as to make it difficult to adjust, you may be able to use a trick I have found can work fairly well: find a thin plastic rod like piece of material. I have previously used a length of ridged tube as supplied with an aerosol spray can. Glue this to the top of the inductor's core. Take great care not to let any glue go down the sides and gum up the thread! Once the glue is completely set, you might be able to adjust the core by rotating the new attachment. A gentle upwards force might be required if the core has gone off the bottom of the thread.
regarding new audio input signal, you could have attached it directly to one of the existing inputs of the audio amp in the cassette unit, pin 5 or 6. This way your external input would look exactly like the internal cassette signal from the ula perspective, without any additional components (except coupling capacitor and maybe resistor divider to bring down the input level to the amp)
david rollor It ought to mean the level from the AY sound generator is higher than it usually is with a 10k ohm resistor for R37. If you want to make the changes I described in the video, I would think it'd be fine to leave R37 as it is. Do make sure you've correctly identified R37. The service manual says it should be 10k ohms and I don't think I've seen a +2 where it wasn't. However, I wouldn't be at all surprised if different values were used in some units.
JoulesperCoulomb I changed the rest of the resistors to the values in the video, sounds much better. I double checked R37 to make sure and it definitely is a 2K2 resistor fitted which I've just left as it is. Cheers.
Very detailed set of videos, thanks. I'm looking for help if you have any suggestions. I have a spectrum zx +2 like this one and the motherboard looks the same as the one in this video. My problem is with the cassette deck, though. The play button doesn't stay down at all when I press it. If I press and hold it connects fine, but as I'm sure you can imagine it isn't ideal for loading software to be constantly pressing it. I opened up the case to see if I could figure out what is wrong with it, but it's out of my depth of knowledge. if you have any ideas of what I could try, I would be grateful!
I haven't very closely examined the mechanical parts of one of these cassette units and so I don't think I can be of much help. It sounds to me as if it ought to be possible to repair it. Clearly whatever causes it to latch in the Play position is broken/worn out/missing. Perhaps someone else here will know what to do. I also suggest posting a request for help in the forums at the World of Spectrum web site. It might be helpful to post a photograph or two of your cassette unit as a few different variations were used in the +2.
Hi! Great Spectrum repair video's you make!! I've bought my first spectrum 2+ yesterday. And maybe you can help me with the problem I have with it. When in push the Play, FF or FB button on the build in data recorder the screen gets really blurry. And when I released it the screen is normal again. Thanks for any reply!!
It's common and probably normal for there to be a slight disturbance of the picture when the cassette motor switches on or off, but if there is significant disruption while the motor is running, then something is wrong. As always, there could be quite a few causes, but I suggest checking for the following: - Degraded power supply smoothing capacitors in the +2 and/or its power supply unit could lead to such problems. If not already done, it's probably worth replacing all the electrolytic capacitors, including the one (I think there's normally only one, but replace any others too) in the cassette unit. Note that my experience is that bonding between the copper and the circuit board is particularly fragile in the grey cased +2 and so you should be extra careful to avoid damaging any pads or tracks. I suggest cutting through the leads of capacitors and removing each individually, if possible. I recommend you don't attempt this work yourself if you have no experience of component level repair of electronic equipment. - Dirty switch contacts in the switch that energises the motor when the cassette player's keys are pressed. - Wear/dirt/lack of lubrication where required/incorrect or worn out belt in the cassette mechanism or inside the motor unit causing the motor to have to work unusually hard and so put greater strain (and probably noise too) on the power supply.
Empirically, I ended up with very similar values: R45 = 33 kΩ, R37 = 2.2 kΩ. However, because C28 and R37 form an RC circuit and we can't make assumptions about amplifier's input impedance, it would be probably best to increase also the capacity of C28 so that all audible frequencies from the sound generator can pass. I think 2 μF-ish should be already on the safe side and 4,7 μF is totally bulletproof even in case of negligible input impedance because 1 / (2 * pi * 2200 Ω * 20 Hz) = 0.000003619 F.
punkojosh I haven't attempted such a repair without it, so I couldn't be certain. However, that part of the button has to take quite a bit of force and so I strongly recommend reinforcing it.
Hi, I would like to add sound input to my +2 (black model) I have read that the +2 black model is a +2b or basically a +3 without a disc drive, would the Schmitt trigger circuit be necessary and a modded 3.5mm socket on this model or is there an easier way as I'm sure the +3 accepts audio in. Also I am a novice when it comes to electronics, can you explain why it would be a bad idea to just attach a socket to the tape inputs directly or even to use the amplifier that's built into the tape deck, the HA17324 chip seems to have 4 amplifiers on it, can one of them be used? If I do need to add the Schmitt trigger amp circuit would it be possible to use it with a separate 3.5mm jack I would prefer to add a second socket somewhere near the tape deck.Thanks in advance,Chris.
+Chris Flynn It's been a while since I worked on one of the later Spectrum models, so I can't remember all of the details. However... I think the +2A is just like the +3 with regards to audio input/output, but is missing a 1uF capacitor to couple the audio input. If you add that, its audio socket should be just like that on the +3 (in and out via the same socket - you'll need an appropriate lead). The +2B is more-or-less the same as the +2A, but has a PCB track linking the tip and the ring of the audio socket. If you cut that and add the coupling capacitor, then the audio socket should become just like that on the +3. If you look up the circuit diagrams, what needs to be done should be fairly clear in both cases. There are other ways to achieve an audio input on these computers, but the above ought to be the easiest and least destructive. I believe it is possible to feed external audio into one of the unused sections of the amplifier IC on the Spectrum's cassette unit. I didn't look into this very closely, but perhaps I will for a future grey cased +2 project.
+JoulesperCoulomb Firstly thanks for your swift reply it's much appreciated :-)I had a look at the schematics for the +2a and +2b, but I seem to have a strange combination of the 2, my main board is labelled as a +2a (Z70833) Issue 2 1998, but the capacitors resistors and diodes are all labelled as though it's a +2b ie C200, D200, D201instead of C48, D36 D37 etc I found a few examples online where people just attach an input to the negative side of C200, even though I am a complete novice at electronics, this looks wrong to me the schematics shows the ear input going to the positive side of C41 also on my board I notice there is continuity between both terminals of the 3.5mm input socket, it doesn't seem to be a trace that needs cutting it seems as though it's internal in the socket, how would I be best to proceed, could I just add a new socket on the back and feed the signal to the positive side of C200 or would it be better to solder another 1uf cap connecting both negative legs together and then feed my input to the positive side of the new 1uf cap?Thanks again,Chris.
+Chris Flynn If the audio socket is a TRS type, then the tip and ring are almost certainly not internally connected. The PCB track connecting the two may well be under the socket body. I'm fairly sure I've seen a set of instructions for making the change online somewhere. Whether you use the existing socket or add a new one, I suggest connecting the input via a new 1 uF capacitor, with the capacitor's negative terminal connected to the negative terminal of C200(/C48). Connecting the new input to the same point as the cassette player's output might work, but it isn't generally wise to directly connect the outputs of two sources like this.
+JoulesperCoulomb Thanks again for your reply. I am also wondering because my mp3 player, laptop soundcard etc is stereo, if I just use a stereo cable and solder the left and right channel together in the new socket, would that be ok or would this have an affect on volume or damage the sound card or mp3 player, sorry but I am a complete novice as I said or would I be best just using either left or right only? Thanks again, Chris
I really like the external loading modified board, for people who are unable to build one would you consider selling one pre made with just the socket needing attached or better still are you planning on selling them ram module style ;) I personally think they would prove really popular another excellent video .
I probably could, though I haven't any immediate plans to do so. However, someone who is able to make the necessary wiring modifications in the Spectrum, ought not to have too much difficulty in assembling a simple circuit on a stripboard. I could produce a more detailed video guide to assembling and fitting this circuit. I might also consider constructing a small number for sale - if you are interested, please contact me via the form at zx.zigg.net .
JoulesperCoulomb I would like to assemble a circuit like this for my +2. I also have a toast-rack 128K and a 48K which is very temperamental when it comes to loading, even from cassette. Could this type of circuit be easily adjusted and modified to fit to these earlier machines?
david rollor I would think this circuit would work well if used to drive the cassette input of other models of ZX Spectrum. I will carry out some tests when I can find the time.
+JoulesperCoulomb thank you very much for your videos. they are great. I got a ZX Spectrum 128k +2 that didn't work. I replaced the RF modulator and got a very very decent picture. The games load fine. although I'm facing 1 issue. I have a bit of background noise (interference like). This is gone when I disconnect the cassette player. Also after pressing enter to load the cassette, even before pressing play, sound (noise) is getting in making the colour frame around to show up and change colour in a very timely fashion from red to blue. So I believe the problem is somewhere on the small PCB board of the cassette player. Do you think that replacing the capacitors there would solve the problem or would you suspect it to be something else? I would be very thankful if you could point me in the right direction. :)
thats normal its the spectrum "searching", on a machine with the tape deck pressing enter on the loader is basically typing load"" enter, doing this on a 48k does what you describe, it is "waiting" for you to press play, i hope i explained it clearly but dont worry about it what yours is doing is normal.
also if you insisted on providing your own discriminator and amp circuit, you could have employed two unused op amps which are inside the cassette 4 way IC
I replicated your audio in circuit and it works well on my +2. Thanks for posting it.
Excellent! Love the Schmitt Trigger use there and as you proved it works really well! Very impressed! Look forward to the next video!
Really nice circuit! If only the original Spectrums used Schmitt triggering for their tape loading; it would certainly have prevented many a headache.
And the quality of your work is astounding as always. I've seen far too many ugly hacks, and your attention to detail is refreshing.
The russian clones (or at least the Pentagon and Scorpion) did :)
Hans Meier Wow, thanks for the info!
That's a huge amount of repair and mod work to a single machine - well done indeed!
Looking forward to seeing the final result.
Cheers, John
I always enjoy these videos, I don't understand most of the complicated bits being only a humble electrical contractor. I can see though that you take enormous pride in the quality of work which is always nice to see.
Anyway I have started to cut my teeth on minor electronic products as a bit of a hobby including the +3 sound fix and building small boards for composite video on my Atari 2600jr and my Phillips Videopac. Luckily even though I don't understand what is happening I can follow the circuit diagrams.
Thank you for these videos they are very inspiring. :)
What a delight is to watch your videos.
Love your videos, really helped me sort out my +2. Always had trouble loading cassette tapes, so having a go at the mod in this video. Just a few small alterations in mine, i.e. I removed R47 and used the top as output for internal cassette and bottom as input for new circuit. I added the removed 680ohm resistor to the output of the new circuit board.
Fantastic video! Enjoyed watching with detailed instructions, wealth of knowledge and step by step instructions! Great that you used multiple angles for video recording! Superb editing and videos, keep them coming! :)
Hi, as you know from my other comments I'm having trouble connecting an external audio source to my +2b, I thought using a 1uf cap connected to the negative terminal of C200/(C41) would route the Audio exactly as the original schematic, but I am getting no sound in, if I omit the capacitor and connect my line in straight to the negative terminal of C200 it works no problem, now I am a complete novice at electronics and I thought I heard the word coupling capacitor somewhere so I had to look up what one did, I don't want to cause more future damage by omitting the cap, from what I read a coupling cap lets ac through and blocks dc which makes sense to me so far as audio should be AC, next I looked up the value of the cap to use for audio and it turns out there are different values for different frequency's, now call me crazy but wouldn't a digital source (cd player/mp3/sound card etc) have a different frequency to an analogue source (old tape players) so now I am wondering if I know my mp3/wav is recorded at 44.1khz would this be radically different from the intended analogue tape source and if so would a rough guess at a 44nf cap work? or 0,05uf, it's the only thing that would make sense to me or have I got that totally wrong, sorry for such a noob question, but as my electronics skills are basic I can only guess.
Regards, Chris.
A detailed guide would be great,i think i would like one of these but first need to fix
the rf sound i mentioned, after checking from your advice the rod was crushed but when touched brought the sound back briefly
I assume you mean the core of inductor L5. As I noted they are rather delicate. If it is smashed to bits you're going to have to replace the inductor or perhaps you'll be able to find a suitable replacement core. You'll probably have to remove the inductor from the PCB to get the damaged core out.
However, if just the top portion of the core is damaged so as to make it difficult to adjust, you may be able to use a trick I have found can work fairly well: find a thin plastic rod like piece of material. I have previously used a length of ridged tube as supplied with an aerosol spray can. Glue this to the top of the inductor's core. Take great care not to let any glue go down the sides and gum up the thread! Once the glue is completely set, you might be able to adjust the core by rotating the new attachment. A gentle upwards force might be required if the core has gone off the bottom of the thread.
Another fantastic and interesting video
regarding new audio input signal, you could have attached it directly to one of the existing inputs of the audio amp in the cassette unit, pin 5 or 6. This way your external input would look exactly like the internal cassette signal from the ula perspective, without any additional components (except coupling capacitor and maybe resistor divider to bring down the input level to the amp)
My +2 has a factory fitted 2K2 resistor at R37. R38=18K and R45=10K. Not sure if this would cause any problems.
david rollor It ought to mean the level from the AY sound generator is higher than it usually is with a 10k ohm resistor for R37. If you want to make the changes I described in the video, I would think it'd be fine to leave R37 as it is.
Do make sure you've correctly identified R37. The service manual says it should be 10k ohms and I don't think I've seen a +2 where it wasn't. However, I wouldn't be at all surprised if different values were used in some units.
JoulesperCoulomb I changed the rest of the resistors to the values in the video, sounds much better. I double checked R37 to make sure and it definitely is a 2K2 resistor fitted which I've just left as it is. Cheers.
Very detailed set of videos, thanks. I'm looking for help if you have any suggestions. I have a spectrum zx +2 like this one and the motherboard looks the same as the one in this video. My problem is with the cassette deck, though. The play button doesn't stay down at all when I press it. If I press and hold it connects fine, but as I'm sure you can imagine it isn't ideal for loading software to be constantly pressing it. I opened up the case to see if I could figure out what is wrong with it, but it's out of my depth of knowledge. if you have any ideas of what I could try, I would be grateful!
I haven't very closely examined the mechanical parts of one of these cassette units and so I don't think I can be of much help. It sounds to me as if it ought to be possible to repair it. Clearly whatever causes it to latch in the Play position is broken/worn out/missing. Perhaps someone else here will know what to do. I also suggest posting a request for help in the forums at the World of Spectrum web site. It might be helpful to post a photograph or two of your cassette unit as a few different variations were used in the +2.
JoulesperCoulomb good to know, I'll do that thanks
Hi! Great Spectrum repair video's you make!! I've bought my first spectrum 2+ yesterday. And maybe you can help me with the problem I have with it. When in push the Play, FF or FB button on the build in data recorder the screen gets really blurry. And when I released it the screen is normal again. Thanks for any reply!!
It's common and probably normal for there to be a slight disturbance of the picture when the cassette motor switches on or off, but if there is significant disruption while the motor is running, then something is wrong.
As always, there could be quite a few causes, but I suggest checking for the following:
- Degraded power supply smoothing capacitors in the +2 and/or its power supply unit could lead to such problems. If not already done, it's probably worth replacing all the electrolytic capacitors, including the one (I think there's normally only one, but replace any others too) in the cassette unit. Note that my experience is that bonding between the copper and the circuit board is particularly fragile in the grey cased +2 and so you should be extra careful to avoid damaging any pads or tracks. I suggest cutting through the leads of capacitors and removing each individually, if possible. I recommend you don't attempt this work yourself if you have no experience of component level repair of electronic equipment.
- Dirty switch contacts in the switch that energises the motor when the cassette player's keys are pressed.
- Wear/dirt/lack of lubrication where required/incorrect or worn out belt in the cassette mechanism or inside the motor unit causing the motor to have to work unusually hard and so put greater strain (and probably noise too) on the power supply.
Empirically, I ended up with very similar values: R45 = 33 kΩ, R37 = 2.2 kΩ. However, because C28 and R37 form an RC circuit and we can't make assumptions about amplifier's input impedance, it would be probably best to increase also the capacity of C28 so that all audible frequencies from the sound generator can pass. I think 2 μF-ish should be already on the safe side and 4,7 μF is totally bulletproof even in case of negligible input impedance because 1 / (2 * pi * 2200 Ω * 20 Hz) = 0.000003619 F.
Currently fixing a broken play button on a Spectrum +2.
How essential is that metal bracket reinforcement?
punkojosh I haven't attempted such a repair without it, so I couldn't be certain. However, that part of the button has to take quite a bit of force and so I strongly recommend reinforcing it.
You can use winamp with a plugin to load tap files they play as audio then.
Hi, I would like to add sound input to my +2 (black model) I have read that the +2 black model is a +2b or basically a +3 without a disc drive, would the Schmitt trigger circuit be necessary and a modded 3.5mm socket on this model or is there an easier way as I'm sure the +3 accepts audio in. Also I am a novice when it comes to electronics, can you explain why it would be a bad idea to just attach a socket to the tape inputs directly or even to use the amplifier that's built into the tape deck, the HA17324 chip seems to have 4 amplifiers on it, can one of them be used? If I do need to add the Schmitt trigger amp circuit would it be possible to use it with a separate 3.5mm jack I would prefer to add a second socket somewhere near the tape deck.Thanks in advance,Chris.
+Chris Flynn It's been a while since I worked on one of the later Spectrum models, so I can't remember all of the details. However...
I think the +2A is just like the +3 with regards to audio input/output, but is missing a 1uF capacitor to couple the audio input. If you add that, its audio socket should be just like that on the +3 (in and out via the same socket - you'll need an appropriate lead).
The +2B is more-or-less the same as the +2A, but has a PCB track linking the tip and the ring of the audio socket. If you cut that and add the coupling capacitor, then the audio socket should become just like that on the +3.
If you look up the circuit diagrams, what needs to be done should be fairly clear in both cases. There are other ways to achieve an audio input on these computers, but the above ought to be the easiest and least destructive.
I believe it is possible to feed external audio into one of the unused sections of the amplifier IC on the Spectrum's cassette unit. I didn't look into this very closely, but perhaps I will for a future grey cased +2 project.
+JoulesperCoulomb Firstly thanks for your swift reply it's much appreciated :-)I had a look at the schematics for the +2a and +2b, but I seem to have a strange combination of the 2, my main board is labelled as a +2a (Z70833) Issue 2 1998, but the capacitors resistors and diodes are all labelled as though it's a +2b ie C200, D200, D201instead of C48, D36 D37 etc I found a few examples online where people just attach an input to the negative side of C200, even though I am a complete novice at electronics, this looks wrong to me the schematics shows the ear input going to the positive side of C41 also on my board I notice there is continuity between both terminals of the 3.5mm input socket, it doesn't seem to be a trace that needs cutting it seems as though it's internal in the socket, how would I be best to proceed, could I just add a new socket on the back and feed the signal to the positive side of C200 or would it be better to solder another 1uf cap connecting both negative legs together and then feed my input to the positive side of the new 1uf cap?Thanks again,Chris.
+Chris Flynn If the audio socket is a TRS type, then the tip and ring
are almost certainly not internally connected. The PCB track connecting
the two may well be under the socket body. I'm fairly sure I've seen a
set of instructions for making the change online somewhere.
Whether you use the existing socket or add a new one, I suggest connecting the input via a new 1 uF capacitor, with the capacitor's negative terminal connected to the negative terminal of C200(/C48).
Connecting the new input to the same point as the cassette player's output might work, but it isn't generally wise to directly connect the outputs of two sources like this.
+JoulesperCoulomb Thanks again for your reply.
I am also wondering because my mp3 player, laptop soundcard etc is stereo, if I just use a stereo cable and solder the left and right channel together in the new socket, would that be ok or would this have an affect on volume or damage the sound card or mp3 player, sorry but I am a complete novice as I said or would I be best just using either left or right only?
Thanks again,
Chris
+Chris Flynn It would be best to connect only the left or right channel of your audio source to the Spectrum's new input.
I really like the external loading modified board, for people who are unable to build one would you consider selling one pre made with just the socket needing attached or better still are you planning on selling them ram module style ;) I personally think they would prove really popular another excellent video .
I probably could, though I haven't any immediate plans to do so. However, someone who is able to make the necessary wiring modifications in the Spectrum, ought not to have too much difficulty in assembling a simple circuit on a stripboard. I could produce a more detailed video guide to assembling and fitting this circuit. I might also consider constructing a small number for sale - if you are interested, please contact me via the form at zx.zigg.net .
JoulesperCoulomb I would like to assemble a circuit like this for my +2. I also have a toast-rack 128K and a 48K which is very temperamental when it comes to loading, even from cassette. Could this type of circuit be easily adjusted and modified to fit to these earlier machines?
david rollor I would think this circuit would work well if used to drive the cassette input of other models of ZX Spectrum. I will carry out some tests when I can find the time.
+JoulesperCoulomb thank you very much for your videos. they are great.
I got a ZX Spectrum 128k +2 that didn't work. I replaced the RF modulator and got a very very decent picture. The games load fine. although I'm facing 1 issue.
I have a bit of background noise (interference like). This is gone when I disconnect the cassette player. Also after pressing enter to load the cassette, even before pressing play, sound (noise) is getting in making the colour frame around to show up and change colour in a very timely fashion from red to blue. So I believe the problem is somewhere on the small PCB board of the cassette player. Do you think that replacing the capacitors there would solve the problem or would you suspect it to be something else?
I would be very thankful if you could point me in the right direction. :)
thats normal its the spectrum "searching", on a machine with the tape deck pressing enter on the loader is basically typing load"" enter, doing this on a 48k does what you describe,
it is "waiting" for you to press play, i hope i explained it clearly but dont worry about it what yours is doing is normal.
The best ever
also if you insisted on providing your own discriminator and amp circuit, you could have employed two unused op amps which are inside the cassette 4 way IC
I can't Believe how much Damage this ZX Had., PS contact Cement works great for Repairs.
How can u thumps down this vid? You 2 who did are bellends! Lol