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ADC Range Adjustment

ADC Range Adjustment

2019-06-28 by Max

Greetings to all, I'm new to this group,
thanks to the moderator for accepting me and to all for the help I'm receiving already, by reading your old posts and thanks to let me share my troubles, not finished yet.
  I own my Polaris since mid 90s, I remember when I bought it to have no idea of what it was, i only knew it was the little brother of the Chroma a friend had and that had impressed me so much. For many years it has been my favorite synth, after a flooding it occurred more than 15 years ago my  unit unfortunately died . Brought to a synth repair center in Italy, the diagnose was that the synth had the switch panel failure, but the repair cost was too high as it needed a dedicated panel, well ok...
It remained in the synths Hades, until yesterday, when once installed the new panels (thanks Paul!) the synth returned to a new life. Following the polarisserviceadjustmentscheckout instructions, I made it playable again, it now keeps the tuning well and it doesn't slowly transform sounds in a bubbling mess. The problem is that all sliders are still unresponsive and as soon as i touch them, data are jumping abruptly from a value to the other.
While testing, I noticed that R45 doesn't seems to affect the master LED behavior, adjusting it the LED remains OFF. If I touch the MASTER slider instead, the LED turns ON and it turns OFF if I place the slider in the MID position (this looks strange to me).
Apart this, the only problem I found in the tests is the voltage at P3 pin1, where I find 2.86v instead 3v.
Thank you!
Max



www.maxpro.audio

RE: [chromapolaris] ADC Range Adjustment

2019-06-28 by Paul D. DeRocco

> From: Max <sndgroom@...>
>
> I own my Polaris since mid 90s, I remember when I bought it
> to have no idea of what it was, i only knew it was the little
> brother of the Chroma a friend had and that had impressed me
> so much. For many years it has been my favorite synth, after
> a flooding it occurred more than 15 years ago my unit
> unfortunately died . Brought to a synth repair center in
> Italy, the diagnose was that the synth had the switch panel
> failure, but the repair cost was too high as it needed a
> dedicated panel, well ok...
> It remained in the synths Hades, until yesterday, when once
> installed the new panels (thanks Paul!) the synth returned to
> a new life. Following the polarisserviceadjustmentscheckout
> instructions, I made it playable again, it now keeps the
> tuning well and it doesn't slowly transform sounds in a
> bubbling mess. The problem is that all sliders are still
> unresponsive and as soon as i touch them, data are jumping
> abruptly from a value to the other.
> While testing, I noticed that R45 doesn't seems to affect the
> master LED behavior, adjusting it the LED remains OFF. If I
> touch the MASTER slider instead, the LED turns ON and it
> turns OFF if I place the slider in the MID position (this
> looks strange to me).
> Apart this, the only problem I found in the tests is the
> voltage at P3 pin1, where I find 2.86v instead 3v.

As long as the CPU is running, P3-1 is okay, it's just a logic level reset line.

If the instrument got flooded, it's almost certain that the sliders are full of crud. There were two different sliders used in different versons. If you have the small white body ones, you can buy replacements here:

https://syntaur.com/rhodes_polaris.html

but they're expensive. If you have the larger yellowish metal ones, they're harder to find.

You should first try repairing them, though. If you carefully unsolder them, you can take them apart and clean the wiper contacts and tracks with Q-tips and alcohol, then put them back together and reinstall them. While they're open, you should also make sure the wiper contacts are straight, which you can usually fix with sharp tweezers. I've had pretty good luck with this, but you might not be able to get all of them working. But better to have to replace a couple of them than all of them.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-06-28 by sndgroom@...

Thanks for your advise, Paul.
Even if in the flooding the synth hadn't direct contact with water, it took weeks until I went back home and realized what had happened, due to moist sure oxidation occurred, I hope I can still save them after all these years. Very soon I'll start cleaning the sliders and let you know if this is enough, or I need to replace them.

RE: [chromapolaris] ADC Range Adjustment

2019-07-06 by sndgroom@...

After a careful cleaning of all sliders, nothing changed. What is strange is that measuring their values with a tester they look like working fine as variable resistors. I'm thinking it might be the MUX and ordered some chips to check. Any suggestions?
Thank you!

RE: [chromapolaris] ADC Range Adjustment

2019-07-06 by Paul D. DeRocco

> From: sndgroom@...
>
> After a careful cleaning of all sliders, nothing changed.
> What is strange is that measuring their values with a tester
> they look like working fine as variable resistors. I'm
> thinking it might be the MUX and ordered some chips to check.

It's hard to see noisy pots with a meter. The best way to see if the sliders are dirty is to put a scope probe on the wiper as you move it up and down in normal operation, to see if the line on the screen remains clean as it rises and falls. If the slider is dirty, you'll see obvious discontinuities and erratic behavior. But obviously you can't do that unless you have access to a scope.

I'd need a more precise description of the behavior to guess what else might be wrong. Are you getting the same behavior from all sliders, or are some bad and others okay? Can you swap the 4051 muxes, and see if the bad behavior moves to different sliders? Do the levers work okay, or do you get erratic output from them too? (They go through the same mux.)

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-06 by sndgroom@...

Thanks Paul,
yes, I have a scope, thanks for the tip, I'll try that.
Regarding the sliders behavior, it is erratic everywhere, pedal and levers included.
The sliders practically do not affect anything, just towards the mid position, they jump to random values.
If left in that position, my Polaris starts modulating everything, something like a S&H on filters and some other craziness, like drunk.
A few 4051 are on order already, I hope they'll arrive soon.
Ciao :)





---In chromapolaris@yahoogroups.com, <pderocco@...> wrote :

> From: sndgroom@...
>
> After a careful cleaning of all sliders, nothing changed.
> What is strange is that measuring their values with a tester
> they look like working fine as variable resistors. I'm
> thinking it might be the MUX and ordered some chips to check.

It's hard to see noisy pots with a meter. The best way to see if the sliders are dirty is to put a scope probe on the wiper as you move it up and down in normal operation, to see if the line on the screen remains clean as it rises and falls. If the slider is dirty, you'll see obvious discontinuities and erratic behavior. But obviously you can't do that unless you have access to a scope.

I'd need a more precise description of the behavior to guess what else might be wrong. Are you getting the same behavior from all sliders, or are some bad and others okay? Can you swap the 4051 muxes, and see if the bad behavior moves to different sliders? Do the levers work okay, or do you get erratic output from them too? (They go through the same mux.)

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-06 by Paul D. DeRocco

> From: sndgroom@...
>
> yes, I have a scope, thanks for the tip, I'll try that.
> Regarding the sliders behavior, it is erratic everywhere,
> pedal and levers included.
> The sliders practically do not affect anything, just towards
> the mid position, they jump to random values.
> If left in that position, my Polaris starts modulating
> everything, something like a S&H on filters and some other
> craziness, like drunk.

Yeah, it sounds like it's not the sliders. That's good, because everything else is easy to replace. It could be the ADC0804 converter, but as long as you have the scope, you may be able to figure out what's wrong.

There should be 0V and 5V on the two ends of the sliders, and each wiper should produce a clean 0V to 5V range as you move the slider. Then, if you look at the ADC line, you should see a time-multiplexed version of all the sliders and other inputs. That pattern should be duplcated on the input to the ADC (Z54-1 or Z53-6). Make sure there's 2.5V on the reference input (Z54-7 or Z53-9). If everything looks cool, then I'd suspect Z53. If there's a problem in the muxes, you'll probably see something wrong in the ADC value, or perhaps even at some of the slider wipers.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-12 by sndgroom@...

Thanks Paul for the detailed instructions, really appreciate.
I was going to do these tests, but before starting I tried to slightly tap the chips of the AD/DA section to see if  some oxidation in the slots was maybe giving the problems. Turning it back on, with surprise, my Polaris is now sounding same as my chainsaw! :( What I only hear now, is a loud modem-like digital sound.
Before writing back to you with new problems, I tried to see what happens but cannot find anything wrong.
Thanks so much for your patience and help!

RE: [chromapolaris] ADC Range Adjustment

2019-07-12 by Paul D. DeRocco

> From: sndgroom@...
>
> Thanks Paul for the detailed instructions, really appreciate.
> I was going to do these tests, but before starting I tried to
> slightly tap the chips of the AD/DA section to see if some
> oxidation in the slots was maybe giving the problems. Turning
> it back on, with surprise, my Polaris is now sounding same as
> my chainsaw! :( What I only hear now, is a loud modem-like
> digital sound.
> Before writing back to you with new problems, I tried to see
> what happens but cannot find anything wrong.

You may have nudged a pin onto an oxidized spot. I'd try completely pulling various chips and reseating them, so that you get some good wiping action as you slide the pins in and out. And be very careful that you don't accidentally fold a pin underneath the chip, so it's not actually in the socket.

But I can't give you any better advice because I don't really know what it sounds like. Do you hear the "digital" sound on top of the audio, or no audio at all? How loud is it, compared to a normal audio signal?

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-12 by sndgroom@...

The previous term I used to describe the sound I get, fits pretty well: sawchain
Imagine a very loud 90s modem, the sound when connecting to internet in those times, something  like pink noise modulated by a S&H, that gets re-triggered each time I push a key. No, no synth sounds at all. :(
I tried removing and reinstalling the D/A chips, unfortunately nothing changed.
If useful, I can upload a video to let you hear the noise.
Thanks so much!

RE: [chromapolaris] ADC Range Adjustment

2019-07-12 by Paul D. DeRocco

> From: sndgroom@...
>
> The previous term I used to describe the sound I get, fits
> pretty well: sawchain
> Imagine a very loud 90s modem, the sound when connecting to
> internet in those times, something like pink noise modulated
> by a S&H, that gets re-triggered each time I push a key. No,
> no synth sounds at all. :(
>
> I tried removing and reinstalling the D/A chips,
> unfortunately nothing changed.
> If useful, I can upload a video to let you hear the noise.

Could be helpful. Something that bad sounds like more than a bad chip, like a bad ground connection or bad power supply.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-13 by sndgroom@...


Yes, it seems strange such a dramatic change only by moving a bit a few chips.  I double checked and their legs are OK and correctly placed into their slots. I'll try checking with more attention the power supply, but measuring yesterday around the ICs, all looked like OK.
Thank you! :)

Re: [chromapolaris] ADC Range Adjustment

2019-07-13 by Florian Anwander

Thanks for the video.

We hear the digitalsound  all the time. This means, either some digital signal is influencing the outputsignal all the time. This means, either a part in the output path, or a general fault in the supply. It could be the 4053's, which switch between main out and alt out. And also it could be a missing ground somewhere.

I'd check with a scope, whether the signal appears on the supply voltages on various places.

Florian

Am 13.07.19 um 08:55 schrieb sndgroom@... [chromapolaris]:
 

Yes, it seems strange such a dramatic change only by moving a bit a few chips.  I double checked and their legs are OK and correctly placed into their slots. I'll try checking with more attention the power supply, but measuring yesterday around the ICs, all looked like OK.
Thank you! :)

RE: [chromapolaris] ADC Range Adjustment

2019-07-14 by Paul D. DeRocco

> From: sndgroom@...
>
> https://youtu.be/zI1MFh6nINc
>
> Yes, it seems strange such a dramatic change only by moving a
> bit a few chips. I double checked and their legs are OK and
> correctly placed into their slots. I'll try checking with
> more attention the power supply, but measuring yesterday
> around the ICs, all looked like OK.

If it's really that loud, then you should be able to see it on the output board, on Z3-1. If you see it there, check the MAIN OUT and DATA AUD inputs to the board. Is it affected by the master volume control? If not, does the master volume control vary the MAIN VOL voltage?

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

Re: [chromapolaris] ADC Range Adjustment

2019-07-14 by sndgroom@...

Thanks for your reply.
I made some tests with the scope yesterday night:
First thing I noticed is that rubbing with the scope's negative crocodile the main motherboard's ground, the digital noise tended to get higher in pitch to almost a pitched tone.
Even if I didn't test all of the  ICs, I noticed that the line Z18, Z28, Z30 had no pulse at their pins, only noise.
All changed after touching TP2 with the same probe, the noise totally stopped and I had the digital pulse back to those ICs pins. he problem now is that the synth is totally mute, even with the scratch patch.
Doing some diagnostics tests this morning, I found this:
D3= all lights on, but only when I'm holding the switch. As soon as I remove the finger the LEDs turn off (it wasn't like that)
D4=ADC Range, still I cannot turn on the LED while moving R45, but until I do not fix the A/D, I believe it is normal.
Many thanks!

RE: [chromapolaris] ADC Range Adjustment

2019-07-14 by sndgroom@...

Thanks Paul,
at Z3-1, I see some signal, but not a pure Pulse wave, it looks like mixed with noise.
As explained on the previous message, the noise disappeared but the synth makes no sound now.

RE: [chromapolaris] ADC Range Adjustment

2019-07-14 by Paul D. DeRocco

> From: sndgroom@...
>
> I made some tests with the scope yesterday night:
> First thing I noticed is that rubbing with the scope's
> negative crocodile the main motherboard's ground, the digital
> noise tended to get higher in pitch to almost a pitched tone.
> Even if I didn't test all of the ICs, I noticed that the
> line Z18, Z28, Z30 had no pulse at their pins, only noise.
> All changed after touching TP2 with the same probe, the noise
> totally stopped and I had the digital pulse back to those ICs
> pins. he problem now is that the synth is totally mute, even
> with the scratch patch.
> Doing some diagnostics tests this morning, I found this:
> D3= all lights on, but only when I'm holding the switch. As
> soon as I remove the finger the LEDs turn off (it wasn't like that)
> D4=ADC Range, still I cannot turn on the LED while moving
> R45, but until I do not fix the A/D, I believe it is normal.

You should always have a connection between the scope ground and a circuit ground near where you're trying to look. It's best if you use the clip on the probe, but running a separate ground line and clipping it to one of the bare lugs sticking up on the board is useful. I seem to recall there's one near the DAC, or maybe between the memory array and the rest of the board. Or, you could use TP1 as a ground. But if you're grounded far from where you're looking, you'll get a noiser view. If you're only grounded through the AC line cord, you'll get tons of noise on the display.

Touching the ground clip to TP2 will prevent the DAC from working at all, probably driving the DAC line to one rail or the other, depending upon the input offset.

If you have a decent scope ground, what do you see on the DAC line? You ought to see a repeating pattern of voltages, as it refreshes the sample-and-hold circuits. You might be able to lock onto it by adjusting the variable time base of your scope, or just triggering off the most positive or negative voltage in the sequence. I'd be curious to know what you see. To get anything meaningful, though, you'd have to force all the voices to be enabled by using LF, E, and then making sure 1 to 6 are turned on. Playing should then cause various voltages in the DAC sequence to change. I would expect to see voltages that cover most of the -5V to +5V range.

And I'm still curious if you can vary the MAIN VOL line on the output board by adjusting the master volume slider.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

Re: [chromapolaris] ADC Range Adjustment

2019-07-14 by Florian Anwander

Am 14.07.19 um 09:48 schrieb 'Paul D. DeRocco' pderocco@...
[chromapolaris]:
> You should always have a connection between the scope ground and a
> circuit ground near where you're trying to look.
Just another pitfall: I once mis-seated a connector, so there was no
ground connection between a troublesome pcb and the supplies. But due to
the circuits circumstances the pcb itself had created a virtual ground,
which made me measure "reasonable" values on the pcb itself. My lesson
from that is, that I now measure the ground lines first.

Florian

RE: [chromapolaris] ADC Range Adjustment

2019-07-14 by sndgroom@...

Thanks Paul, for the explanation on how to use a scope. I agree regarding the good ground, that's why I was using the two copper lids on the motherboard, that I surely wrongly called "main" ground in the previous message. I need from you, if possible, confirmation on where to measure the DAC, is it R47 pins a good place? If that's OK, I read a pulse, but pretty weak and not well defined.
I attach a couple of pictures.
Many thanks!

RE: [chromapolaris] ADC Range Adjustment

2019-07-14 by sndgroom@...

>And I'm still curious if you can vary the MAIN VOL line on the output board by adjusting the master volume slider.
Unfortunately,  even moving the volume slider, I cannot read anything anywhere on the output board, :(

RE: [chromapolaris] ADC Range Adjustment

2019-07-14 by Paul D. DeRocco

> From: sndgroom@...
>
> Thanks Paul, for the explanation on how to use a scope. I
> agree regarding the good ground, that's why I was using the
> two copper lids on the motherboard, that I surely wrongly
> called "main" ground in the previous message. I need from
> you, if possible, confirmation on where to measure the DAC,
> is it R47 pins a good place? If that's OK, I read a pulse,
> but pretty weak and not well defined.

Yes, either side of R47 is fine.

The R47Hameg pic shows various stepped waves, which is normal, assuming the scale is one or two volts per div. The R47miniscope pic shows a couple of different levels. If you slow the sweep down, you should see more steps. After all, there are 38 sample-and-holds, so there are 38 time-slots in the repeating pattern. They're not fixed width, because the software takes different amounts of time to compute each one. But at 0.1ms per div, you're only seeing a small part of the sequence. If you zoom out to see more of it, and you play keys, you might see voltages moving up and down. They'll jump around horizontally unless you find something else to trigger off with a separate probe, like the SLOW line going to ZX01 on one of the channels.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-15 by sndgroom@...

Yes, I can now see the pulses "dancing" while playing note!
The setting on R46 was, I believe" responsible as as soon as I moved the pot, the flow of waves started.
BTW, still no sound. Anything else I can do?
Many thanks!

RE: [chromapolaris] ADC Range Adjustment

2019-07-15 by Paul D. DeRocco

> From: sndgroom@...
>
> Yes, I can now see the pulses "dancing" while playing note!
> The setting on R46 was, I believe" responsible as as soon as
> I moved the pot, the flow of waves started.
> BTW, still no sound. Anything else I can do?

Unless R46 is broken, it shouldn't have any major effect. All it does is null the op-amp offset, so that the DAC will be as linear as possible, and the tuning will be accurate. If turning R46 makes a significant sudden change, I'd replace it. Otherwise, you should adjust it until you've got as close to 0V between the two test points as you can measure, ideally with a meter with 100uV resolution.

Are you sure you have anything in the memory? It's common to get no sound if you haven't gone through the calibration procedure outlined in the service manual.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-15 by sndgroom@...

A couple of things more I found:
The ADC converter 0804 is hot!
Even hotter discovery:
Imagine a square occupying the space from Z29 down to the COMP SIDE text on the motherboard: Anything I push with the back of the screwdriver cancels the signal on the scope, something serious I believe, like a crack on the PCB? OMG! :(

RE: [chromapolaris] ADC Range Adjustment

2019-07-15 by sndgroom@...

Ehm...so sorry for panicking for no reason, before. Tapping now the ICs, I do not get the same affect anymore,
all looks good! I think it was the probe's crocodile not connecting well to the resistor.
My apologies!

RE: [chromapolaris] ADC Range Adjustment

2019-07-15 by sndgroom@...

>Are you sure you have anything in the memory? It's common to get no
sound if you haven't gone through the calibration procedure outlined in the service manual.
No, I made a total reset, but I loaded a scratch program for the setup.
Done the calibration once again, but still no sound.
Thanks Paul for your patience and time!

RE: [chromapolaris] ADC Range Adjustment

2019-07-15 by Paul D. DeRocco

> From: sndgroom@...
>
> The ADC converter 0804 is hot!

Probably needs to be replaced. But first make sure that Z54-1 and Z54-7 have reasonable voltages on them. The latter should be 2.5V, tweakable via the R45 trimpot. The former should have a sequence of 24 different voltages from 0 to 5V, reflecting the positions of the sliders, etc. Make sure neither is significantly outside the 0 to 5V range, because, even with the clamp diodes, that could be pushing current through the ADC input protection diodes, heating it up. If that looks okay, then definitely replace the 0804.

This certainly accounts for getting no sound. It can't measure the position of any slider, including the master volume control.

Anything else feel hot? ;-) Except the CPU, that is--that's always hot.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-16 by sndgroom@...

So great having your support, thanks Paul! :)
I only repaired analog devices, I'm learning many new things that sure will be useful in the future.
I checked Z54: Pin1 has 2.67v while pin7, 2.51v
I ordered a new ADC on ebay, I hope it will not take too long ..
Ciao!

RE: [chromapolaris] ADC Range Adjustment

2019-07-16 by sndgroom@...

>The former should have a sequence of 24 different voltages from 0 to 5V
With the scope, I can see the seq and how the shapes change when I move the sliders, cool!
Doesn't this mean that the ADC is working good? If so, why the sliders weren't affecting the sound?
Thanks!

RE: [chromapolaris] ADC Range Adjustment

2019-07-16 by Paul D. DeRocco

> From: sndgroom@...
>
> With the scope, I can see the seq and how the shapes change
> when I move the sliders, cool!
>
> Doesn't this mean that the ADC is working good? If so, why
> the sliders weren't affecting the sound?

No, it means the multiplexers that switch the various sliders and deliver their voltages to the ADC are working, but the ADC isn't measuring those voltages because it's blown out. I expect that when you've replaced it, lots of things will suddenly start working. When that happens, the first thing you should do is repeat at least those parts of the calibration procedure that involves sliders and other analog inputs.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-18 by Paul D. DeRocco

> From: sndgroom@...
>
> Unfortunately I replaced the ADC0804, but nothing changed,
> there must be something else too.
> If I understood correctly
>
> http://www.rhodeschroma.com/?id=polarisserviceadjustmentscheckout
> on the "What To Do If You Lose Your Memory" after a total
> reset ant tune all, I should have a scratch sound,
> instead my polaris s totally silent

Is the new 0804 running cool? If so, there was still something wrong with the old one, and it needed to be replaced. You should also look at pins 2, 3, and 5 to see if there's any activity. You should see regular active-low strobe pulses on START ADC, you should see EOC going low a short time later, and then see a strobe pulse on RD ADC. The strobes are down in the microsecond range, but EOC stays low until the data is read, or maybe until the ADC is started again. If you don't see any activity, the CPU may be unable to communicate with the ADC, in which case you'd have to work backward to see if Z28 is generating those strobes, and if Z29 can read EOC.

As to the tuning failure, Tune All will disable all the channels if the CPU is unable to control the synthesizer channels, or unable to measure what they are doing. There are lots of things involved in that:

1) The computer needs to be able to control the DAC voltage.

2) It needs to be able to control the sample-and-hold circuits, to deliver the appropriate DAC voltages to the synth channels.

3) It needs to be able to control the latches that set the analog switches in the synth channels, including the one that diverts the output of a channel into the ALT OUT line during tuning.

4) The output board needs to convert the ALT OUT into the SYNTH ZCD line going back to the main board.

5) The CPU needs to be able to select a subdivision of the SYNTH ZCD frequency, and route it into the timer input so that it can measure its period.

There's a lot of circuitry in there. However, by forcing the channels back on after the tuning fails, or bettery yet, forcing one easily accessible channel back on, you can play on that channel, and see if you have reasonable control over it. Can you get the oscillator to play over a wide range of frequencies? If you crank the filter resonance, does it oscillate? Can you hear any sound from the channel through the audio output? Does it respond to sliders or levers?

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-18 by sndgroom@...

The new ADC0804 is running cool, that's good news!
I'll measure around the ICs tonight and report.
> Can you get the oscillator to play over a wide range of frequencies? If you crank the filter resonance, does it oscillate? Can you hear any sound from the channel through the audio output? Does it respond to sliders or levers?
Unfortunately, I only hear the normal hum in the background, I had tried the filter auto-oscillation already, but nothing, total silence. Moving the faders I hear some digital noise and some clicks pushing the buttons
Thanks!

RE: [chromapolaris] ADC Range Adjustment

2019-07-22 by sndgroom@...

I've been waiting some time before answering and tried in the meanwhile to read as much as I could about digital circuits, to be sure I wasn't alarmed for nothing. What I can now deduce is that the processor could be stuck somewhere. The only digital signal I see are less that 1v in amplitude and mixed with noise.
This is something that happened last week, the synth was almost working, maybe measuring around I bridged something causing the fault?
So sad!

Re: [chromapolaris] ADC Range Adjustment

2019-07-22 by Bob Grieb

Check the reset signal and the clock signal to the CPU chip. Without those
it can't work.

If the CPU really is toast, you can get one on ebay. It's in a socket, so not such
a big deal.

Bob
On Monday, July 22, 2019, 5:57:49 AM EDT, sndgroom@... [chromapolaris] <chromapolaris@yahoogroups.com> wrote:




I've been waiting some time before answering and tried in the meanwhile to read as much as I could about digital circuits, to be sure I wasn't alarmed for nothing. What I can now deduce is that the processor could be stuck somewhere. The only digital signal I see are less that 1v in amplitude and mixed with noise.
This is something that happened last week, the synth was almost working, maybe measuring around I bridged something causing the fault?
So sad!


RE: [chromapolaris] ADC Range Adjustment

2019-07-22 by Paul D. DeRocco

> From: sndgroom@...
>
> I've been waiting some time before answering and tried in the
> meanwhile to read as much as I could about digital circuits,
> to be sure I wasn't alarmed for nothing. What I can now
> deduce is that the processor could be stuck somewhere. The
> only digital signal I see are less that 1v in amplitude and
> mixed with noise.
>
> This is something that happened last week, the synth was
> almost working, maybe measuring around I bridged something
> causing the fault?

The various things you've been seeing indicate that the CPU was running. If it had crashed, you wouldn't see any sequence of stepped voltages on the ADC or DAC lines.

But if you're no longer seeing those, either, yes, I'd check the DC OK line which resets the CPU until the power supply comes up. If you've got the old supply with the R17 trimmer next to the LED, and the LED is off, then you need to turn the trimmer just to the point where the LED turns on, plus another ten degrees or so. That's the most likely thing that would stop the CPU from running, if it was running before.

But if you're not seeing anything more than 1V, check the power supplies themselves. Measure them right where they plug into the main board. Also, are any LEDs on? If they're not within 5% of what they should be, that could be a problem.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-22 by Lou Champagne

Just a thing to check.

I had a similar problem and it had me stuck for months. I finally located a bad 3 pin RAM selection jumper switch on the board. It had become slightly corroded. Once replaced  with a nice new gold one (including jumper), things started working properly. My bad for not checking it earlier. Anyway it’s easy to rule it out and maybe worth checking.

Good Luck and Best Regards.

Lou

 

 

From: chromapolaris@yahoogroups.com [mailto:chromapolaris@yahoogroups.com]
Sent: July-22-19 11:01 AM
To: chromapolaris@yahoogroups.com
Subject: Re: [chromapolaris] ADC Range Adjustment

 

 

Thank you Bob,

I cannot read any pulse there neither, glad to know the 80186 looks easy to find and not expensive.

RE: [chromapolaris] ADC Range Adjustment

2019-07-23 by Paul D. DeRocco

> From: Lou
>
> I had a similar problem and it had me stuck for months. I
> finally located a bad 3 pin RAM selection jumper switch on
> the board. It had become slightly corroded. Once replaced
> with a nice new gold one (including jumper), things started
> working properly. My bad for not checking it earlier. Anyway
> it’s easy to rule it out and maybe worth checking.

It's a good idea, in an old Polaris that isn't running, to reseat every connector, including partially lifting and reinserting every socketed chip. There are a number of jumpers, including a 4x4 block of pins that routes interrupts and DMA requests. Sliding each jumper off and on a couple of times is a good idea. I've not seen any that were fatally corroded, but I suppost that can happen if there was enough moisture.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

RE: [chromapolaris] ADC Range Adjustment

2019-07-23 by sndgroom@...

Many thanks Lou,
it is a good idea to check those too. I sprayed some contact cleaner and moved them a bit, unfortunately in my case it didn't work

RE: [chromapolaris] ADC Range Adjustment

2019-07-23 by sndgroom@...

Thank you Paul,
I made a few tests this morning:
@ Z59 (ADC0804) I can see pulses changing while I play the keys, this should be enough to exclude a fail in the CPU, I believe.
+5v Digital= It was 5.09v, I set it back to 5.00v. If I try LFD3, all LEDs are on, a couple have a bit less brillance but something minimal. I noticed after a second the LF function is disengaged without my action.
Ref +5v= It was 5.01v
Nominal DC lvl= it was a bit out, fixed
ADC Range= this time it worked, turning the LED on
DAC Null= Fixed
After all this and a total reset, loading a scratch patch, I cannot hear any sound