Ensoniq VFX SD mainboard troubleshooting

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Ashe37 » Tue May 09, 2017 9:19 am

The display that is in there isnt a LED, its a vacuum fluorescent display.I've never seen an alternate replacement.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Tue May 09, 2017 2:23 pm

GiliRose wrote:Hi - Boy am I happy to have found this thread!

Help: VFX-SD DEAD DISPLAY ISSUE

I just got a VFX-SD off its original owner for $98, mostly for the nostalgic value.
The synth powers up - small yellow light for a sec in the floppy drive, a sec later the "Sounds" LED lights up
as well as the Bank selector. Otherwise the display is dead.
Navigating blindly I can change banks and select patches using the six push-buttons around the screen.
The synth seems to be OK - all 60 sounds sounded OK and keyboard response was OK too.

I am slowly working my way through page 12 of the Service Manual:
- Reset Sequence / Hard Reset had no effect
- Checked connectors - pulled them out and re-seated a few times to wear out any corrosion,
they seem fine to me - no effect
- Fuses are OK
- I disconnected the 4 pin display cable - no effect (screen still dead, no self-test mode)

I have yet to check the PSU voltages but my gut feeling is that this is something simple, as the synth plays great
(I actually like the less than obvious sounds and it has a characteristic "punch" to it that is good fun).

Any tips and pointers would be great, and Rasputin - your input is incredible!
If it plays "blind" then it tells you a couple things. Everything on the mainboard is probably good. The 6500/11 is at least partially good because it is communicating with the mainboard. So the problem with the display can be down to a couple things. There are voltages specifically allocated to drive the display. These could be bad. There are also driver chips on the display board. Those could be bad. Of course, the actual display itself could be bad.

The first thing I would do is make sure all the voltages needed for the display are making it across the power header to the display board. There are two headers on the display board, one is a 4-pin connector which carries info back and forth between the display and the mainboard. The other connector is what you want to test for voltages. The proper voltages are listed in the service manual.

Like I said, could be any number of things from the VFD needing to be replaced, something grounding out, bad solder joint, bad power lead to the display board, etc. First thing you need to rule out is power supply though.

But be careful. Aside from the actual power switch / transformer area where the AC mains voltage come into the VFX, the display has the highest voltage -- so take precautions!

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Thu May 18, 2017 10:47 am

OK - I checked the PSU voltages on all 3 connectors and they all seemed
within the specified range. So, I guess this really means the actual LED
display unit is a gonner. I suppose my options are:

1. Locate a NOS/Working VFX-SD display board and replace whole unit
(Syntaur possible, though with their prices I might as well buy a new synth)

2. Locate a NOS/Working VFX display board and replace the LED display unit
Any exact guidelines on how to go about this will be appreciated
:roll:

3. Anyone know where I can source the actual display as an individual part?

Thanks

G.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by adamstan » Thu May 18, 2017 11:46 am

It isn't available as new part. However, AFAIR same VFD (not LED) display unit is used in TS10, TS12, EPS, ASR-10, ESQ-1 and SQ-80, so you can pull it from any of these.
Man with a tape recorder | Living in the '80s ;-)

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Thu May 18, 2017 2:00 pm

GiliRose wrote:OK - I checked the PSU voltages on all 3 connectors and they all seemed
within the specified range. So, I guess this really means the actual LED
display unit is a gonner.
Not necessarily true. There are chips which drive the VFD which could be the problem. Plus, even if it appears to be the display itself that is faulty, it might not even be the display proper. Could be some bad soldering connected to the display or any number of things which would prevent it from working even though it's not truly dead.

Or... it could be simply a dead VFD. But I'd try to rule out some other options, if possible.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Thu May 18, 2017 5:19 pm

Rasputin wrote:Or... it could be simply a dead VFD. But I'd try to rule out some other options, if possible.
So glad you are all here to help! I'm all for ruling out the OTHER options :)

I did manage to trace the power line all the way up to the VFD (new word here), so if the VFD is actually fine
(I couldn't see any bad connections, good continuity) - it must be one of those (controller?) chips next to it.

(Please god, make it be one of those chips, they seem easy enough to source and replace... :beg: )

What am I looking for now?

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Fri May 19, 2017 3:29 pm

There should be two different types of VFD driver chips on the display PCB -- Texas Instruments TL5812N and TL4810AN. Unlike the 6500/11, they aren't proprietary so they should be obtainable somehow. The TL5812N is still less than $10 usually, and I'm sure there must be a stockpile of TL4810AN ICs in some random Asian warehouse, if nothing else.

But here's where it gets messy because it could be any number of things. Some big ones are that all the driver chips should have 5VDC, 50VDC, and a clock signal.

:arrow: BE CAREFUL WITH THE 50 VOLT LINE!!!

The TL5812 ICs should have 5V on pin 28, and also 50V on pin 1.
The TL4810 ICs should have 5V on pin 6, and also 50V on pin 15.

Look at 6500/11 pin 29 and pins 31~38 (skipping 30). These are tied to the driver ICs. We know the 6500/11 works at least partially, but we need to verify that it is talking to the VFD drivers.

Pin 31 on the 6500/11 should send a clock signal to both TL5812 chips on their pin 15.
Pin 32 on the 6500/11 should send a clock signal to all TL4810 chips in their pin 4.

Also, one of the TL5812 chips passes out serial data on pin 2 to the serial input of the other TL5812 on pin 27, so if the first TL5812 is dead then the second TL5812 won't know what to do.

This should be a proper VFD replacement, but the price is prohibitive compared to just buying a broken ESQ-1 and parting it out or whatever, should the VFD actually be the issue:

http://www.ebay.com/itm/Noritake-Itron- ... 1725959102

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Mon May 22, 2017 8:14 pm

Sorry for the late reply, real life here getting in the way :-)

I am no electronics wiz, so I will be very cautious here.
I got hold of the TL5812N and TL4810AN datasheets and saw the chip pinouts,
so this should go:

TL5812N - PIN 1 - Vcc2 - 50V
TL5812N - PIN 28 - Vcc1 - 5V

TL4810AN - PIN 6 - Vcc1 - 5V
TL4810AN - PIN 15 - Vcc2 - 50V

I assume voltage values are both DC and with respect to GROUND, which means I have to put my Multimeter's
BLACK probe to a GROUND trace on the board and then use the RED probe to get the readings
at these pins. Correct?

I also get the idea of cascading the chips via the serial link, so that's cool :thumbright:

Big question: How would I go about checking the clock signals from the 6500/11 with a Multimeter?
Thanks again
G.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Mon May 22, 2017 9:37 pm

GiliRose wrote:I assume voltage values are both DC and with respect to GROUND, which means I have to put my Multimeter's BLACK probe to a GROUND trace on the board and then use the RED probe to get the readings
at these pins. Correct?

I also get the idea of cascading the chips via the serial link, so that's cool :thumbright:

Big question: How would I go about checking the clock signals from the 6500/11 with a Multimeter?
Thanks again
G.
Yep, that's exactly what you do. Just don't let your probe slip on the 50V pin and connect anywhere else -- that's a big danger.

You can't check the clock with a DMM. An oscilloscope would be the proper way, although if you have a logic probe (which are quite inexpensive) with a high enough frequency (which is all relative to the clock signal you're measuring, of course) then a lot of times you can pick it up.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Tue May 23, 2017 7:23 am

Rasputin wrote: You can't check the clock with a DMM. An oscilloscope would be the proper way, although if you have a logic probe (which are quite inexpensive) with a high enough frequency (which is all relative to the clock signal you're measuring, of course) then a lot of times you can pick it up.
I sort of expected that and managed to get hold of an old analog Tektronix 2215 scope (60 MHz).
I have never used an O-Scope before, and managed to figure out these very basic points:

- I need to make sure the probe is calibrated against the scopes internal test signal
- Need to set the probe for the proper factor: X1 or X10 - ?
- Need to connect the probe's GND wire to a GND point as close as possible to the pin being tested
- Clock signal might show up as something squarish ( a pulse of sorts)

Other than that, its all new territory for me.

As to A Logic Probe, that would take me a while to get my hands on (live out in the countryside),
but they seem simple enough to use.
Assuming I get one, where would I hook up its +/- connectors with respect to the 6500/11?
Also - what readout would I be on the lookout for?
Any starter-level Logic Probe recommendations ?

Thanks

G.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Thu May 25, 2017 7:39 pm

Just finished the voltage check. I think we have a dud.
I wonder what you make of it:

TL5812N - PIN 1 - Vcc2 - 50V - Dead, no voltage
TL5812N - PIN 28 - Vcc1 - 5V - OK, 4.8V

TL4810AN - PIN 6 - Vcc1 - 5V - OK, 4.8V
TL4810AN - PIN 15 - Vcc2 - 50V - Dead, no voltage

As a ground reference, I used the ground-side leg of the (coupling?) capacitor closest
to the J2 (larger connector) GND pin. Good place for a crocodile hookup :-)

As this was consistent on ALL chips, I assume it has to be something common.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Anongrey » Fri May 26, 2017 4:34 am

Hey y'all just picked up a vfx-sd with the keyboard calibration error for $35 and want to restore this beauty to its previous self. I've hardwired the board and checked the ribbon cable and still have cal error. I've also pulled the KPC ics and removed corrosion and reseated.

I've read earlier that it looks like my next logical step is a replacement of the 8Mhz crystal or the Motorola control IC. I think it would be easiest to replace the crystal first since it's cheaper than a $30 replacement from syntaur. Any suggestions? Once I ignore the calibration error everything else works seamlessly with an external keyboard.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Fri May 26, 2017 12:18 pm

Anongrey wrote:Hey y'all just picked up a vfx-sd with the keyboard calibration error for $35 and want to restore this beauty to its previous self. I've hardwired the board and checked the ribbon cable and still have cal error. I've also pulled the KPC ics and removed corrosion and reseated.

I've read earlier that it looks like my next logical step is a replacement of the 8Mhz crystal or the Motorola control IC. I think it would be easiest to replace the crystal first since it's cheaper than a $30 replacement from syntaur. Any suggestions? Once I ignore the calibration error everything else works seamlessly with an external keyboard.
$35??! I'm clearly living in the wrong place!!! :)

Here's something to think about: When you press "Ignore" on the display keypad, that keypress is routed through the KPC board and only THEN returned to the mainboard. Therefore, if you can override the keyboard calibration error with a keypress then the KPC circuit in question has to be working, at least partially.

If it's working at least partially then the clock and voltage to the 68HC11 chip is good. I would suspect that the 68HC11 is also talking to the KPC firmware chip successfully. The next step is to figure out if there's a dead pin on the chip, if there's a problem in the keyboard proper, or if there's a problem with the other rare Motorola chip which does the actual low-level keyboard scanning.

These are assumptions and generalities, of course, so you'll have to rely on your own brainpower and what you actually see in front of you as far as behavior. But I'd look carefully at the header pins which connect the keyboard proper to the KPC board, and I'd take a logic probe to the proprietary Motorola chip to see if it's sending/receiving traffic on all the pins it is supposed to. Pins 2~5 are not connected to anything, but everything else has a function. Pins 18~21 are directly tied to the keyboard so might not be a bad place to look.

It could also be as simple as the SN7406 inverter. It's part of the loop between both the Motorola ICs and the keyboard itself, so if any of its gates are dead then keyboard no-worky.
Last edited by Rasputin on Fri May 26, 2017 12:56 pm, edited 2 times in total.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Fri May 26, 2017 12:45 pm

GiliRose wrote:As this was consistent on ALL chips, I assume it has to be something common.
That heavily implies the VBB rail is down. That would come in on the power supply header for the display PCB. That header supplies:

9VAC <--- Note: AC (for the display filaments)
+12VDC for the analog sliders [data/volume] (unrelated to your issue at present, but probably fine at any rate)
+5VDC for the standard digital IC power supply (which you've measured is present)

and...

+50VDC which then goes to a 63V capacitor and directly on to the chips in question which measure no voltage.

You seemed to report that 50V was making it onto the display PCB, so if it's not present at the chips then it's a fair chance that either that 63V capacitor is wonky or there's a break in the VBB rail somewhere between the 63V cap and the driver chips. Either one of those would be an excellent outcome.

In other words, double check that there is 50V on the display power header. Then check the same on the 63V capacitor. If you're still measuring 50V then carefully inspect the trace all the way from the + leg of the 63V cap to the next point (should be one of the driver chips) and make sure there are no breaks.

Don't forget that this is 50V, so don't get complacent.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Fri May 26, 2017 2:06 pm

I just got in and saw your message - Wow - Hope!!!
I will check this out ASAP - Thanks!

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