Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

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Frisco
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Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Sun Feb 07, 2021 11:54 pm

Help!

My Roland D-50 has an issue playing patches that use PCM waveforms, but plays all SYNTHE-only patches just fine. PCM waveforms sometimes play fine for a few times and then start cracking or stop playing completely. Sometimes they only produce a 'click' and after hitting some keys it's like something is 'popping' open and the PCM waveform is played correctly again, but always with a cracking sound.

Chorus and Reverb chips are okay, since the problem only arises with PCM waveform patches and the SYNTHE sounds also go through these chips afaik and sound fine. That's why I think the DAC and everything towards the outputs is fine as well. So it's probably something before the DAC.

Now, where to look?

What I did so far:
- replaced the battery
- reloaded the factory patches via MIDI
- ToneRAM reset via key 0 + Data Transfer
- performed the internal tests, multiple times, memory is (appears) ok
- unplugged and replugged all connectors
- checked mainboard for any visible issues to components
- recalibrated the MSB trimpot via procedure in service manual
- changed voltage on the mains transformer from 220V to 240V (230V in my country)
- changed all capacitors on both PSU and mainboard (...)

I'd love to get this awesome synth going again, so all help is greatly appreciated!
Last edited by Frisco on Mon Feb 08, 2021 5:10 pm, edited 1 time in total.

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by meatballfulton » Mon Feb 08, 2021 1:18 am

Do you have schematics? I'd focus on the ROM that holds the PCM waves (too obvious?).
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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Mon Feb 08, 2021 10:22 am

Thanks for your reply. I have the schematics and tried to back trace down from the DAC. I also suspected the PCM ROMs, but my guess would be if they're faulty, they would never produce a waveform, and the 'popping open' in my mind would more suggest an analogue component, like caps? Note I did not replace the SMD caps, but did measure them (in circuit) and they seem to be ok (all have same resistance and charge/decharge similarly).

One thing I forgot to mention: it appears that Reverb presets 17-32 influence the cracking patches , some reverbs in this range even end up in a sort of feedback loop resulting in lots of digital noise. Could that be a RAM issue (either tone RAM or working RAM)? Is there any way I can test that without replacing all RAM ICs?

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Mon Feb 08, 2021 5:08 pm

This thread shows a similar story, but unlike my D-50, Jeeper73's had cracking sound always, not only for the PCM tones...

http://forum.vintagesynth.com/viewtopic.php?t=78276

The solution to his issue however was a very unusual one... One thing his journey proofed is that replacing parts is not always helping, as I learned with replacing all caps...

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Thu Feb 11, 2021 11:36 pm

I did some further measurements on the mainboard, on the resistor arrays (in circuit). Most RA's are measuring values that make sense (15K-ish) but on RA10 (next to the CPU) 2 of the 8 resistors measure 10K instead of 15K ohms. RA10 is attached to the higher address lines (Ah). Afaik, these RA's are used as pull-up resistors to make sure to always get a clear 0 (ground) or 1 (5V). Could these 10K resistors (if it's a correct measurement, being in circuit) result in random ROM/RAM locations being addressed and read and as a result, the distorted PCM patches?

Did some further testing with the standard patches. D50 Voices is one that is failing most of the time, but interestingly, if I turn on the D50 with this patch selected, I can play 2 notes that sound clear and the 3rd one starts cracking/failing until only clicking is heard with consequent notes. When I turn the device off and on again, I can play 2 clear notes again and it starts failing again. As if something is charging and reaching some critical level, like a failing capacitor. But since the SYNTHE patches sound crystal clear, it must be in the digital domain, but where to look for this issue? Running out of ideas.... :(

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Thu Feb 18, 2021 12:17 am

Did some further experimenting with clearing out all patches and starting off with the most simple patch, consisting of only an Upper Partial 1 (rest muted), structure PCM-PCM (#6), no Reverb/Chorus, simple on/off envelope, waveform coarse tuning to C3 and selecting Marimba as PCM waveform. That sounds just fine, without distortion/noise/cracking.

By scrolling through the list of PCM waveforms something interesting happens: waveforms Marimba (#1) until Clarinet (#31) sound fine, but moving on to Breath (#32) and further starts the noise/distortion! Furthermore, after having selected Breath and moving back to Clarinet, the distortion remains for a second before Clarinet sounds fine again...

So there seems to be some cut-off location, possibly moving from PCM ROM IC1 to IC2..?

Experimenting with the Loops in the PCM waveforms: some loops sound fine, others are distorted. I assume that these loops are made up out of one or more single waveforms from the first set.

I also switched from Upper Partial 1 to the other partials and set up the same tone there, but the effects are similar, so it's not the Upper or Lower circuitry, it's failing earlier in the chain.

Does this behaviour point to some suspect component that I can check further?

Because the distorted waveforms are sometimes more and sometimes less distorted (but always noisy) I'd think the suspect ROM IC2 is actually delivering the right data, but it gets distorted somewhere down the line. However, looking at the schematics I cannot figure out where to look...

Should I replace the (which?) SMD caps?

Anybody any ideas? Suggestions highly appreciated!!

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Thu Feb 18, 2021 11:31 pm

To further narrow down the issue, I've set up 3 basic patches with only 1 partial, PCM only (structure 6):

1. PCM waveform 1, Marimba
2. PCM waveform 32, Breath
3. PCM waveform 100, Loop24

Tone 1 always sounds clear. Tones 2 and 3 are mostly distorted, however!

When I switch off and on the D-50, the first 3 or 4 key presses for tones 2 and 3 sound clear and only after 4-6 key presses they start cracking and sometimes failing completely (only clicking/popping).

Interestingly, using tone 3 (which is looped), after switching off and on the D-50, if pressed and hold for a long time, the sound remains clear without distortion! Only after triggering this loop tone multiple times it starts cracking.

In some cases, switching from tones 2 or 3 back to 1, this tone also sounds distorted for the first 2-3 keypresses and then sounds clear again and remains clear.

My conclusion from this behaviour: PCM ROM IC2 is ok, it can deliver the correct data. Something in between is failing. I'm suspecting noisy addresslines in the higher area's of the memory map, therefore affecting only the waveforms from nr 32 and higher... does this make sense and if so, where to look?
Maybe the pull-up resistor arrays on the addresslines? I've measured these before and saw some lower resistance values (10K instead of 15K), but that would end up with a solid 5V as well, right?
Could also be the 0,1uF smd decoupling/bypass capacitors near the memory ICs that I haven't replaced yet.

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Sun Feb 21, 2021 11:43 pm

Off-topic, but just wondering: how does the CPU on the D-50 mainboard address all the memory (ROM/RAM) that it's using? I did some line tracing on the schematics and found the following.

- The CPU is capable of addressing 64kB (16 address lines) external memory
- The Program ROM is 64kB (not sure if everything is used, but all 16 address lines are wired)
- There is 32kB of Tone RAM holding the config of all 64 patches (essentially what you sysex bulk-dump), with battery-backup
- And there's 8kB of Working RAM for the CPU (for managing state/settings/MIDI buffer/etc?)

There is also 8kB of Chorus RAM and 48kB of Reverb RAM, but that doesn't seem to be directly addressed by the CPU, but by the dedicated Chorus and Reverb ICs. Just like the PCM ROM ICs A and B (2x128kB=256Kb, 18 address lines wired) are directly addressed by the Synthe DSP.

Question is: since there is already 64kB of ROM, how can the CPU also address the 32+8=40kB of RAM? My guess would be at power-on the CPU reads the Program ROM and initializes the other devices like Synthe DSP, Chorus, Reverb and Dynascanboard and then magically remaps memory so that part of the 64kB map points to this 40kB of RAM. I see some lines of I/O port 0 going to the chip enable lines of these RAM ICs, that might explain it. Anyone with more info on how this works exactly?

And another question that popped up while reading the schematics: the digitial audio data is 16bit throughout the D-50 (Synthe > Chorus > Reverb > DAC). However, the service manual speaks of 20-bit D/A conversion. The PCM54 IC is 16bit, and there is an additional 4bit R/2R circuit that is attached to the lower 4 bits of the 16bits audio data, that is again fed into the PCM54 as a feedback signal??? What's the purpose of this, how does it affect the output sound?
Last edited by Frisco on Tue Feb 23, 2021 10:12 am, edited 1 time in total.

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Robber1956 » Sun Feb 21, 2021 11:59 pm

Hi Frisco,

I don't know if this is of any help with the D50 but I own a D110 and I had crackling probs too.
Especially with the reverb but also after the release. I opened up the d110 and with the power on all of a sudden I felt that one of the IC's (have to open up again to see which) was real hot on one side. Checked everything and decided to resolder the legs.

After this the crackling was gone so it is possible that with your D50 there is a cold solder joint somewhere as well.

https://www.sequencer.de/pix/roland/d110_open.jpg

https://www.synthxl.com/wp-content/uplo ... -Notes.pdf

I can't remember which was the one with the cold solder joint but they must have at least some similar chips I guess.

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Mon Feb 22, 2021 11:14 am

Hi Robber1956, thanks for taking the effort to reply and your suggestion, I'll check that!

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Re: Roland D-50 noise issue with PCM sounds, SYNTHE sounds fine

Post by Frisco » Sat Feb 27, 2021 4:17 pm

Checked the ICs for heat, but nothing remarkable. Did resolder/reflow the solder on the PCM ROM ICs and most of the SMD caps (the 0.1uF next to the ICs), replaced C59 (33pF), but unfortunately, the crackling issue remains... Could the issue be somewhere else than on the mainboard..?

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