Acquired a near mint +2 - Modding advice needed.

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WDeranged
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Acquired a near mint +2 - Modding advice needed.

Post by WDeranged »

I recently got given a near mint Speccy +2 and a nice 14" Sony Trinitron TV. It was quite an experience opening her up and seeing how clean and immaculate the internals were :D

Anyway, the RF output is (as expected) messy but still better than I remember from my childhood. I eventually ordered an RGB cable from Retro Computer Shack and now I have near pristine output (although the image is decentred) but the AY/beeper balance from the audio output is way off.

After a bit of research I replaced R37 with a 2.2k resistor and it bumped up the AY volume but no where near enough. There is also a ton of background hum (mostly cleaned up by disconnecting the tape deck) and the sound is noticeably thin compared to what I'm getting through the RF output.

So really I have two questions right now. Is it normal for the audio output sound to be much thinner (low bass) compared to the RF and why am I getting an RGB image that is shifted to the left when the RF out is perfectly centered?
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Ast A. Moore
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Re: Acquired a near mint +2 - Modding advice needed.

Post by Ast A. Moore »

It’s not enough to only change the value of R37. I also recommend changing R45 to a 33 kOhm resistor to balance the two audio sources out.

I don’t remember that making the sound tinnier on any of my mods. Some interference is normal, but generally, it’s barely noticeable. I’d check your cable’s shielding or other potential sources of EMI. Could also be a peculiarity of your TV. Perhaps it expects a different load on its audio input. Impedance mismatch can often result in greatly attenuated lower frequencies.

As for the image shifting left or right, that is not unexpected, although I don’t remember it being that drastic. Then again, I usually don’t use the RF output, but comparing the composite and RGB video output form my Toastrack, I can’t see any noticeable shift.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by WDeranged »

Thanks for the quick reply.

Wouldn't changing R45 reduce the level of the ULA audio? I'm hearing very clear beeper audio so I'd rather raise the AY volume to match the ULA otherwise both signals would be swamped in the background hum from the tapedeck's amplifier.

The RGB cable is from Retro Computer Shack and is well regarded so I hesitate to blame it. You could be right about the impedance though, it does sound very much like a mismatch. Though the beeper is coming through very strong and clear, just also lacking bass.

I should probably put the effort in and do a full recap just to remove them from the equation.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by TMD2003 »

Oddly enough, I've had a few troubles with my +2 and the Retro Computer Shack cable. On the LG LCD TV I had a while back, the screen would occasionally move left and right by a few pixels, seemingly at random intervals. On the slightly more modern Panasonic LED TV I have now, the picture is all over the place, to the point where I'm forced to use the RF.

My +2 isn't exactly a sorted example, though, and it's more likely that it has an issue with the RGB output that went undiagnosed for 30 years. It was originally from a Currys Christmas 1987 Bumper Value Pack type package with 90-odd extra games thrown in as well as a nasty SJS-1 joystick, and I reckon it was a "second" from the outset.

I thought I'd mention that, just in case anyone knows the answer.

I also have a +2A/+3 RGB cable, also from RCS, and that works fine on both +2Bs and both +3s.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by akeley »

The image shift may be intrinsic to the Trinitron, some of them act like that when fed RGB sources. It can be a PITA when you have many of them (eg Amiga, which also has its own silly shift, and other micros). My newest Trinitron actually has a function in the menu to adjust this shift, very handy. You can probably adjust it from service menu on your set.

I think the 128 family also has issues with RGB, such as ghosting, though not sure if all of them are affected. Mine (+2A) was modded to alleviate this.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by Ast A. Moore »

WDeranged wrote: Wed Apr 15, 2020 6:57 pm Wouldn't changing R45 reduce the level of the ULA audio? I'm hearing very clear beeper audio so I'd rather raise the AY volume to match the ULA otherwise both signals would be swamped in the background hum from the tapedeck's amplifier.
Yes, it would, but there’s no way around it. You can’t drop the resistance of the AY audio forever. You can always bring the overall audio level up. The 2.2/33 kOhm values make for an almost perfect balance between the AY and ULA audio.

I’ll have to look at the schematic and see if the sound from the Datacorder feeding into the audio can be attenuated as well.


EDIT: I just rechecked, and Increasing the value of R45 will also drop the output of the audio from the Datacorder, but if that’s not enough, you can also increase the value of R80.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by payty »

TMD2003 wrote: Wed Apr 15, 2020 7:19 pm Oddly enough, I've had a few troubles with my +2 and the Retro Computer Shack cable. On the LG LCD TV I had a while back, the screen would occasionally move left and right by a few pixels, seemingly at random intervals. On the slightly more modern Panasonic LED TV I have now, the picture is all over the place, to the point where I'm forced to use the RF
Image shifting is because of the bad blanking signal. I've had this problem on my 128k toastrack. The rgb out conector does not offer such a signal and the available rgb cables use other signal together with a capacitor to obtain it. This does not always work.

Fix is here, on the same website:

https://www.retrocomputershack.com/RCS- ... index.html

I have a perfect and steady image now.


For the thread initiator. Could sound noise be because of the modulator? Usually spectrums are av-modded and modulators are disconnected from power supply.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by TMD2003 »

Good to know there's a fix! Not so good to know it'll require soldering that might be beyond the limits of my already limited coordination, and definitely beyond the limits of my current soldering iron.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by WDeranged »

Ast A. Moore wrote: Wed Apr 15, 2020 8:00 pm
WDeranged wrote: Wed Apr 15, 2020 6:57 pm Wouldn't changing R45 reduce the level of the ULA audio? I'm hearing very clear beeper audio so I'd rather raise the AY volume to match the ULA otherwise both signals would be swamped in the background hum from the tapedeck's amplifier.
Yes, it would, but there’s no way around it. You can’t drop the resistance of the AY audio forever. You can always bring the overall audio level up. The 2.2/33 kOhm values make for an almost perfect balance between the AY and ULA audio.

I’ll have to look at the schematic and see if the sound from the Datacorder feeding into the audio can be attenuated as well.


EDIT: I just rechecked, and Increasing the value of R45 will also drop the output of the audio from the Datacorder, but if that’s not enough, you can also increase the value of R80.
Ahh I see what you mean. I've got a 33k resistor somewhere in my box so I'll give it a go in a few days. Is there any consensus on whether the tape amp hum is coming through either R80(tape) or R45(beeper)? Or Both? I quite like my tape loading noise and would prefer to keep it loud :D

*edit* Actually I'm a bit confused. If R45 affects Datacorder output volume what does R80 do?

On the subject of RGB being shifted left I decided to plug the scart lead into my ancient but faithful Sony flat panel. It was near enough exactly as it should be, a little shifted to the right but basically fine. So it does appear that the misalignment is my Trinitron as akeley suggested. I need to get hold of a compatible remote control before I can get into the service menu though :roll:
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Re: Acquired a near mint +2 - Modding advice needed.

Post by Ast A. Moore »

WDeranged wrote: Wed Apr 15, 2020 10:56 pm *edit* Actually I'm a bit confused. If R45 affects Datacorder output volume what does R80 do?
One resistor is in line with the input (R80) and the other with the output (R45). That was done so you could hear the sound if you saved data, too. They are not completely separate, however (at the ULA), so the signal will bleed from one to another.

So, the simplest scenario is this. When you load a game from tape, the signal from the Datacorder goes to the ULA (which interprets it as data), and the audio out jack (and Pin 3 of the RGB connecter) via R80. It is also routed to the FM audio modulator for the RF signal.

When the ULA output sound, it is fed to the Datacorder, as well as to the audio out jack via R45 (and, of course, to the audio modulator via R61).
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Re: Acquired a near mint +2 - Modding advice needed.

Post by WDeranged »

Ast A. Moore wrote: Wed Apr 15, 2020 11:49 pm
WDeranged wrote: Wed Apr 15, 2020 10:56 pm *edit* Actually I'm a bit confused. If R45 affects Datacorder output volume what does R80 do?
One resistor is in line with the input (R80) and the other with the output (R45). That was done so you could hear the sound if you saved data, too. They are not completely separate, however (at the ULA), so the signal will bleed from one to another.

So, the simplest scenario is this. When you load a game from tape, the signal from the Datacorder goes to the ULA (which interprets it as data), and the audio out jack (and Pin 3 of the RGB connecter) via R80. It is also routed to the FM audio modulator for the RF signal.

When the ULA output sound, it is fed to the Datacorder, as well as to the audio out jack via R45 (and, of course, to the audio modulator via R61).
I think I'm understanding you, thanks. One more question though, wouldn't increasing the resistance of R80 reduce the audio level for the data interpreter? If so I'd rather give the ULA as much chance as possible to read crappy old tapes :D

After doing some more testing I've come to the conclusion that my hum woes are mostly related to the Datacorder's amp pcb. When it's entirely disconnected I'm getting spookily clear audio from the rear jack, though the AY output still sounds extremely thin. I think I'll end up fitting a switch or relay (as I've seen suggested elsewhere) to disable it when not in use.

I did quickly add this ground bridge that I've seen suggested elsewhere. I can't hear much difference though.

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Re: Acquired a near mint +2 - Modding advice needed.

Post by Ast A. Moore »

WDeranged wrote: Thu Apr 16, 2020 12:04 am wouldn't increasing the resistance of R80 reduce the audio level for the data interpreter?
Not in the least. In fact, you could remove R80 entirely and it wouldn’t affect the loading of programs.
WDeranged wrote: Thu Apr 16, 2020 12:04 amthough the AY output still sounds extremely thin.
Yeah, that is a bit peculiar. Make sure there are no shorts caused by solder splashes.
WDeranged wrote: Thu Apr 16, 2020 12:04 amI did quickly add this ground bridge that I've seen suggested elsewhere. I can't hear much difference though.
Never heard of that before. I can’t imagine this would help much with the hum.
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and zasm Z80 Assembler syntax highlighter.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by WDeranged »

Ast A. Moore wrote: Thu Apr 16, 2020 10:07 am
WDeranged wrote: Thu Apr 16, 2020 12:04 am wouldn't increasing the resistance of R80 reduce the audio level for the data interpreter?
Not in the least. In fact, you could remove R80 entirely and it wouldn’t affect the loading of programs.
WDeranged wrote: Thu Apr 16, 2020 12:04 amthough the AY output still sounds extremely thin.
Yeah, that is a bit peculiar. Make sure there are no shorts caused by solder splashes.
WDeranged wrote: Thu Apr 16, 2020 12:04 amI did quickly add this ground bridge that I've seen suggested elsewhere. I can't hear much difference though.
Never heard of that before. I can’t imagine this would help much with the hum.
Supposedly the amp pcb on some Taiwanese +2's doesn't make good contact with the metal frame of the datacorder and you get a ground loop. Might be a myth but I thought it was worth a try.

I'll check for solder splashes later but I was quite meticulous. The resistor I used is fairly old and cheap, could this affect the bass response? I did test the audio on my Sony flatscreen and it was also thin so the problem doesn't seem to be related to the CRT.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by Ast A. Moore »

WDeranged wrote: Thu Apr 16, 2020 12:03 pm The resistor I used is fairly old and cheap, could this affect the bass response?
Not very likely, but not impossible either.
Every man should plant a tree, build a house, and write a ZX Spectrum game.

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and zasm Z80 Assembler syntax highlighter.
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Re: Acquired a near mint +2 - Modding advice needed.

Post by WDeranged »

Ast A. Moore wrote: Thu Apr 16, 2020 12:10 pm
WDeranged wrote: Thu Apr 16, 2020 12:03 pm The resistor I used is fairly old and cheap, could this affect the bass response?
Not very likely, but not impossible either.
Thought not. Thanks, you're being very helpful :)
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Re: Acquired a near mint +2 - Modding advice needed.

Post by Trox »

Threads revival… I’m experiencing the same with my +2, I’ve cleaned and made sure the Datacorder is properly earthed but the hum persists. When the Datacorder is unplugged the sound is clear and I can ramp the volume up pretty high without issue.

I’ll follow this through and see if I can improve mine
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