Ensoniq ESQ-1 debugging help

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dnigrin
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Ensoniq ESQ-1 debugging help

Post by dnigrin » Fri Jul 02, 2021 1:03 am

I recently acquired TWO non-functioning plastic ESQ-1s. One requires work on the power supply and is a bit more beat up than the other, so I'm concentrating first on the other, nicer one.

The unit starts up in Self Test mode. All buttons display the correct value when pressed, however when pressing Record and Soft Button #1 (to reset the unit), nothing happens - I do not get the "Erase All Memory and Reinitialize" message.

I did continuity checks on the cables connecting the display board to the main board, and all seems fine there.

I did power measurements on the power supply board while fully loaded - all seems good there as well (all values within ranges shown on page 26 of service manual), with one exception; the +V unregulated voltage (between pins 12 and 10) was just slightly higher than the +11V indicated as the highest tolerable amount - it was +11.1V. Not sure that's a big deal.

I tried swapping the main board from the other ESQ-1, and I had the same outcome. However I have no way of knowing if that other main board is OK.

Similarly, I tried swapping the display board from the other ESQ-1 - same outcome. Again, unsure of the status of that other board though.

The unit has no battery in place, but don't think that's required for the synth to operate.

Finally, I tried doing the "hard reset", where one shorts out the right side of C18 to the left side of CR3 on the mainboard, while power is off. I did this, but no change afterwards.

Suggestions for where to go next with this?
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Re: Ensoniq ESQ-1 debugging help

Post by Rasputin » Fri Jul 02, 2021 3:45 pm

dnigrin wrote:
Fri Jul 02, 2021 1:03 am
I tried swapping the main board from the other ESQ-1, and I had the same outcome. However I have no way of knowing if that other main board is OK.
Make sure the DUART on the mainboard you're currently using is sending serial data to the display over its pin 11. If you don't see serial traffic then you need to see if the DUART is otherwise operating.

Essentially, you need to make sure the mainboard is booting, and if it is booting then if the DUART is working. If the DUART seems to be working, but no serial Tx is present then the DUART probably needs to be replaced.

If the DUART has serial Tx then you have to see if the display board is receiving the serial Tx from the DUART.

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Re: Ensoniq ESQ-1 debugging help

Post by madtheory » Fri Jul 02, 2021 8:42 pm

Oh, that's a good tip. I gotta try this with mine it has somewhat similar symptoms. Does some stuff but no sound. I think it is worth checking the ripple on the supply too. I'm planning to test mine before and after a re-cap, on the assumption that after should be better.

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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Fri Jul 02, 2021 11:01 pm

Rasputin wrote:
Fri Jul 02, 2021 3:45 pm
Make sure the DUART on the mainboard you're currently using is sending serial data to the display over its pin 11. If you don't see serial traffic then you need to see if the DUART is otherwise operating.
Thank you very much Rasputin. I'm learning as I go here, so please have patience! I've identified the DUART on my board (confusing, because the schematics I see at Rainer Buchty's site I think are for the metal version, and the DUART there doesn't match on my plastic one). Anyway, I see the chip at U6, it's a Motorola MC2681, and see that pin 11 is the Channel B Transmitter Data Serial Output. All good so far - but can you give details on how I see the traffic? I have my trusty multimeter, but do I need to get out of my old oscilloscope? I'm new enough in the analog world of electronics troubleshooting, but really starting from scratch for digital.... My scope is a Tektronix 2215, 60 MHz, in case it matters: https://w140.com/tekwiki/wiki/2215

I've also explored the incredibly detailed info you provided on this VFX SD thread in case I could glean the above details from there, but I didn't see it... https://forum.vintagesynth.com/viewtopi ... =5&t=96381

Thanks in advance!
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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Fri Jul 02, 2021 11:10 pm

Actually I take that back - I did see this on that other thread; would this also apply to ESQ-1? And if so - "high" and "low" I presume means higher voltages (like how high, 3, 4, 5 volts?), and low means close to zero volts? And checkable with just my regular multimeter? And for all the "pulsing" values - presumably those are what I would need to use a scope to see? Again, thanks for indulging my newb questions!
In general, you'll want to check the UART in this order, for these results:

Pin 20 [GND] - Ground (stuck low, permanently tied to digital ground)
Pin 40 [VCC] - +5VDC (stuck high, permanently tied to voltage)
Pin 32 [X1-CLK] - Clock input (pulsing [@ 5 MhZ], permanently tied to one of the crystals)
Pin 34 [RES] - should briefly hit low on power up, then stay high
Pin 35 [CS] - should be low if chip is enabled, so probably pulsing but maybe low (stuck high or floating = bad!!!)
Pin 10/11 [Serial RX/TX] - should show pulsing traffic, or at least be high at idle (stuck low or floating = bad!!!)
Pin 30/31 [MIDI TX/RX] - same as serial RX/TX above
Pins 16~19 / 22~25 - [D0~D7] - pulsing
Pin 8 [R/W] - pulsing (possibly mostly high with negative blips)

Permanently floating pins are a giant red flag. Pins that are stuck high or low might not be the chip itself, but something connected to the chip instead. For example, something that's generally high like a Tx/Rx pin could be grounding out somewhere else, or D0~D7, R/W, CS, etc. could be improperly fed by the CPU, GLU, or SUPER GLU.
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Re: Ensoniq ESQ-1 debugging help

Post by Rasputin » Sat Jul 03, 2021 2:32 pm

dnigrin wrote:
Fri Jul 02, 2021 11:01 pm
I have my trusty multimeter, but do I need to get out of my old oscilloscope?
Even a logic probe would likely do, but since you have a scope then that will be superior.

When you first power up the Ensoniq, the DUART should send a burst of traffic which initializes the display and brings it out of self-test. If you had some type of serial interface which could capture the traffic then you could even decode it, but simply seeing a bunch of traffic at power on should prove that the mainboard as a whole and the DUART specifically are working enough to try to communicate with the display board.

In a certain sense, you should hope that the DUART serial Tx is what is dead because if it is transmitting then there are only a few easy fixes to hope for, and the problem you do not want to have is that the display processor serial Rx is fried. So although we know the display processor is working enough to run the self-test properly, they have been known to fail in such a way as that they will no longer respond to traffic from the DUART, although the traffic is reaching the display processor input. That cannot be fixed, aside from replacing the display processor.

The fixes to hope for is that the DUART is dead (partially or fully), or that there's simply a bad connection between the DUART and the display processor. There are a couple points of failure where this is possible, but you've (seemingly) already eliminated connection issues between the mainboard and the display--which is the easiest potential fix.

If the DUART does not appear to be firing off any serial communications at power on then you'd want to see if the CPU seems to be active (probably by scoping the data bus and looking for traffic). If the mainboard is not firing up as a whole then there would obviously be a larger problem looming, such as power, clock, or reset signal.

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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Sat Jul 03, 2021 7:11 pm

Rasputin wrote:
Sat Jul 03, 2021 2:32 pm
Even a logic probe would likely do, but since you have a scope then that will be superior.
I didn't know such a thing existed, pretty cool - will have to grab one of those for the future! But in the meantime, I fired up the scope...
Rasputin wrote:
Sat Jul 03, 2021 2:32 pm
When you first power up the Ensoniq, the DUART should send a burst of traffic which initializes the display and brings it out of self-test. If you had some type of serial interface which could capture the traffic then you could even decode it, but simply seeing a bunch of traffic at power on should prove that the mainboard as a whole and the DUART specifically are working enough to try to communicate with the display board.
Here's what I see (going in the order specified from the other thread):

pin 40 [VCC]: +5VDC, steady
pin 32 [X1-CLK]: See a constant, beautiful waveform, with time setting at 0.5 usec/division, about 3.5V
Pin 34 [RES]: Goes high for very brief period, then low. (opposite of what you said would be expected?)
Pin 35 [CS]: See some activity for very brief period, then high. (again, opposite of what you said)
Pin 11 [Serial TXB]: Goes high pretty much right away - maybe?? a very very brief burst of activity before that, but hardly. Definitely less than what I saw on the CS pin for example.

So definitely some funky stuff - assuming my measurements are good.
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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Sat Jul 03, 2021 7:20 pm

Also, since you said the next step (assuming something not right with the DUART) would be to confirm that CPU is active with signal coming from it. I'm assuming the CPU is the big chip next to it - it's this Motorola chip: https://www.cpu-world.com/CPUs/6809/Mot ... B09EP.html

But now I need help again. When I look at the pinouts and descriptions, I'm unsure exactly what pin to probe for the "data bus", and also I don't see a ground pin that I should be putting my scope's ground to?

Thanks again...
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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Sat Jul 03, 2021 7:23 pm

Think I'm answering my own question re: the ground - assuming that's equivalent to Vss pin?
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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Thu Jul 08, 2021 1:02 am

Did I lose you @rasputin?
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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Thu Jul 08, 2021 1:29 am

I took some educated guesses at what the CPU pins were. I assumed Vss was ground, and that Vcc is power. I measured across with my scope and I do get roughly +5V.

I guessed that all the A pins are address, and D pins are data. I then scoped with ground probe on Vss, and positive probe on D0; I got a very regular looking waveform. And similar across D1, D2 and D3 (I stopped there). Although not quite the same shape on each one, I'm definitely seeing a regular signal on each of those.

So with this info, do I assume my CPU is good, and that therefore perhaps it IS my DUART? Or still more potential other things to rule out?
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Re: Ensoniq ESQ-1 debugging help

Post by Rasputin » Thu Jul 08, 2021 1:29 pm

dnigrin wrote:
Thu Jul 08, 2021 1:29 am
Or still more potential other things to rule out?
I would see if the DUART serial Tx is making it across to the display board. The activity on the display side of the board should match the activity directly at the DUART, as far as serial Tx goes. So if you see a small burst of traffic at the DUART then it shouldn't simply disappear into the void when it hits the display.

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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Thu Jul 08, 2021 4:57 pm

So before even seeing if anything got to the display board, I checked pin2 ("Display In") on the pin outs on the mainboard, to see if any outbound signal was there - really, nothing I could see - it basically goes from low to high almost instantly, essentially the same thing I saw on the Serial Tx pin of the DUART. Here's a video of what I see: https://defectiverecords.com/temp/Pin2-Display_In.mp4

Should I just go ahead and order/replace the DUART? And I'm assuming this is something that I won't find any longer at Mouser, etc... and will need to go to eBay or similar?

By the way - THANK YOU again for your assistance. Really incredible that you help people like this, it's greatly appreciated! And I like learning in the process.
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Re: Ensoniq ESQ-1 debugging help

Post by Rasputin » Fri Jul 09, 2021 5:19 am

dnigrin wrote:
Thu Jul 08, 2021 4:57 pm
Should I just go ahead and order/replace the DUART? And I'm assuming this is something that I won't find any longer at Mouser, etc... and will need to go to eBay or similar?
I don't see anything strongly pointing to the DUART yet. One thing to consider is that the 68681 and 2681 are fairly similar, but definitely not identical, nor even compatible. So the VFX and ESQ DUARTs can't be tested 100% in the same ways, although there is considerable overlap.

"Pin 34 [RES]: Goes high for very brief period, then low. (opposite of what you said would be expected?)"

That is one of the differences... the RESET on the 2681 is active high, and on the 68681 it is active low, so the behavior is reversed, and your measurement makes sense in context.

"Pin 35 [CS]: See some activity for very brief period, then high. (again, opposite of what you said)"

This is one thing that has me concerned. Behavior in both the VFX and ESQ *should* be identical here, as they are both active low. If CS is constantly high then that means the DUART is taken off the data bus and cannot talk to the CPU at all.

"Pin 11 [Serial TXB]: Goes high pretty much right away - maybe?? a very very brief burst of activity before that, but hardly. Definitely less than what I saw on the CS pin for example."

Judging by your scope video, you're right that it didn't seem like any traffic at all. But in light of the CS behavior, I'm not really surprised. The DUART with only Tx what is written into the DUART by the CPU. The CPU should boot, read the contents of the ROMs, get the initialization string for the display, send the initialization to the DUART, and the DUART encodes the initialization as serial communication. The display processor sits there listening for serial communication, and once it receives the initialization from the DUART then it comes out of self-test mode.

So you can see that there are many links in the chain which could cause the display to be stuck in self-test. The CPU must boot. That mostly depends on voltage, RESET, and clock (which seem correct). The ROMs have to supply instructions to to the CPU, so they have to be readable. The ROMs and DUART rely on a Chip Select signal to take them on and off the data bus as needed, so that they don't try to talk over each other when the CPU needs to access one of them.

I don't think we've proven that the Chip Select is working yet. We could monitor the CS signal on the ROMs, and also the data pins on the ROMs to see if data is moving around as the CPU gets opcodes from the ROMs. If you can confirm the CPU is reading the ROMs and running code then making sure the DUART Chip Select is bringing the DUART onto the data bus would be a good step after that.

If the DUART Chip Select looks suspect in comparison to the other Chip Selects (such as OSLOW, etc.) then that could be a clue. A couple 74F139 chips interpret the address bus and select/deselect which chip is allowed to talk. If there's a problem in that area then the DUART won't ever be allowed to get the init string from the CPU to send to the display.

Also, take it all with a grain of salt. I don't always know what I'm talking about.

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Re: Ensoniq ESQ-1 debugging help

Post by dnigrin » Fri Jul 09, 2021 8:17 pm

Thanks so much for this great info - will do some scoping and report back with my findings.
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