These are both very plausible explanations.maniacminer wrote: ↑Fri Apr 19, 2024 6:48 pm Although one thing I have noticed is the PSU voltage on the "good" M500 is 4.65V and on the "bad" it is 5.1V maybe the lower voltage prevents the runt pulses from having an effect? Perhaps more modern TTL is fast enough to "see" them?
Music 500 -> Music 5000 and Music 500 -> Music 3000
Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
I think generally runt pulses on the nS0..nS7 signals will not matter as:maniacminer wrote: ↑Fri Apr 19, 2024 6:48 pm There are runt pulses on that 74138, but the other "good" M500 also has them and that somehow doesn't exhibit this problem.
- the signal is connected to a syncronous input (i.e. an input qualified by a seperate clock)
- the signal is OR'ed with the Phi1 clock before being connected to an aynchronous input
I think the only expection to this rule is where nS7 connects to the Async Clear input of IC3 (a 74LS74).
Dave
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
I just soldered a 100pF capacitor on and left it at that. I've got a load more "dead" M500's to fixdaveejhitchins wrote: ↑Fri Apr 19, 2024 6:59 pmThink I'd be wanting to try it out with 5V . . . Just to eliminate the low Voltage being the culprit. - Dave H.maniacminer wrote: ↑Fri Apr 19, 2024 6:48 pm There are runt pulses on that 74138, but the other "good" M500 also has them and that somehow doesn't exhibit this problem. Although one thing I have noticed is the PSU voltage on the "good" M500 is 4.65V and on the "bad" it is 5.1V maybe the lower voltage prevents the runt pulses from having an effect? Perhaps more modern TTL is fast enough to "see" them?
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Ah yes, I was following the schematic with kind of truth table and the window here is very narrow, so the capacitor seems to smooth out runt pulses and extend and delay genuine pulses by a tiny margin (nanoseconds)hoglet wrote: ↑Fri Apr 19, 2024 7:08 pmI think generally runt pulses on the nS0..nS7 signals will not matter as:maniacminer wrote: ↑Fri Apr 19, 2024 6:48 pm There are runt pulses on that 74138, but the other "good" M500 also has them and that somehow doesn't exhibit this problem.
- the signal is connected to a syncronous input (i.e. an input qualified by a seperate clock)
- the signal is OR'ed with the Phi1 clock before being connected to an aynchronous input
I think the only expection to this rule is where nS7 connects to the Async Clear input of IC3 (a 74LS74).
Dave
Oh, I'm so glad I know I'm not losing my mind (although I'd have to find it first, I lost it in a rabbit hole sometime ago)
What amuses me is how many have gone like this and people don't realise? I think having some music tracks from known, good working systems points out that your unit is bad, rather than the Hybrid M500 being just shitty and chalked up to being 80s inferior technology. As when it is working 100% it is a very powerful synthesizer with lots of potential.
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Now I have two working M500's (yay!) Here comes the next two... (all the space I have on the bench at the moment)
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
I pulled one apart today.
I desoldered the usual suspects, but amazingly, these were all good. So I moved on to the rest of the logic. Then I popped IC35, IC34, IC33, IC31 & IC30. Cleaned them up and put them through the chip tester - IC31/74LS173 was bad.
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
I found the RAM has failed and that would explain the lack of wavetable synthesis.
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
After a long walk and a couple of pints, back to the M500...
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Yay! Fixed.
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Onto the next M500...
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
How many Music 500/3000/5000 devices do you have?
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
6½ - three are now working, three and a half to be fixed. The half is just the board with no case (also doesn't work)
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Whilst looking through the vast amount of M500/0 stuff I found a tune I've not heard since I heard an M5000 demonstrated decades ago, so with my three working M5000's all connected via a mixer, playing simultaneously, here's "Hooked on Bach"
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
So this is what the next two M500's sound like without doing anything to them. They are both playing the Bach piece from the previous post. Listen and weep
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Putting the fourth M500 back together and come across a problem I've never had before... Pushing this IC in with my finger and "crunch"
I also discovered one of the 74LS374's popped out of the socket as its legs are too short. Eeeek!Big Model B Econet,Master 512,Electron,A3000,A540,Atom,Unilab 3-Chip Plus,6502,Z80,65C816,80186,32016,Matchbox,ARM7TDMI,Master 10/100,PiCoPro,Teletext,Music500,PiSCSI,Challenger3,Gotek,VideoNuLA,GoSDC,GoMMC,Integra-B,RGB2HDMIv4,Epson LQ-850 (for the win!)
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Fourth tested and now all four play simultaneously
I can't hear any audible difference switching between them on the fly apart from slightly different levels and bass response.
I can't hear any audible difference switching between them on the fly apart from slightly different levels and bass response.
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
Something I did wonder, the output filters have a very strong cut-off, making the high sample rate pointless. I'm just guessing that it is really brutal because of the artefacts introduced by having really tiny wave samples and then stretching them out over a long period leading to sharp transitions? I think I'll remove the capacitors in a unit section by section and listen to the difference. It's a shame the sample RAM is so meagre
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Re: Music 500 -> Music 5000 and Music 500 -> Music 3000
I tried smaller capacitors and as they progressed to resistors the sound got thinner and harsher, I guess that's to be expected.
I have a tray of switching 7805 replacements and thought I'd give it a go. It only needed a couple of capacitors changing and wow, the power consumption drops by over 70%. Performing listening tests, I don't hear any difference in the sound and there's nothing on the scope (the audiophiles go wild) I left it playing all day and the transformer is just tepid. Usually it is absolutely roasting and can't be touched with bare skin. So that's a win if anyone wants to do the mod, it works great. When I replace all the 74F with 74LS (bar one IC) then it will run even cooler
I have a tray of switching 7805 replacements and thought I'd give it a go. It only needed a couple of capacitors changing and wow, the power consumption drops by over 70%. Performing listening tests, I don't hear any difference in the sound and there's nothing on the scope (the audiophiles go wild) I left it playing all day and the transformer is just tepid. Usually it is absolutely roasting and can't be touched with bare skin. So that's a win if anyone wants to do the mod, it works great. When I replace all the 74F with 74LS (bar one IC) then it will run even cooler
- Attachments
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- R_78E_1_0-1711201.pdf
- Switching 7805 data sheet
- (692.33 KiB) Downloaded 1 time
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