Ensoniq VFX SD mainboard troubleshooting

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Ashe37
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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Ashe37 » Thu Mar 16, 2017 4:12 am

And i got a dead vfx for parts for next to nothing and am now wondering if tis repairable

cutoffres
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Re: Ensoniq VFX SD mainboard troubleshooting

Post by cutoffres » Thu Mar 16, 2017 12:38 pm

Inspecting C32 and C31 was my next investigation place, so i must be in the right direction?
measures on the 79l05 are:
Common= 00
Input= -9,05V (the wrong -12 ANALOG voltage)
Output=-4,46V

This 79L05 has got solder flux on the pins, so maybe will replae it at the same time the C32 capacitor on the -12V LINE.
Will let know the next step.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Thu Mar 16, 2017 1:53 pm

My guess (for the little it's worth) is that the -5V regulator is fine. I'd test/replace C32 way before messing with a regulator.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Thu Mar 23, 2017 3:47 pm

Ashe37 wrote:And i got a dead vfx for parts for next to nothing and am now wondering if tis repairable
Everything is repairable in a sense, depending on your personal interpretation of the ship of Theseus paradox. Well, I guess that's not true if it's the only one left in the world and there are no parts to cannibalize and no way to recreate them.

But enough waxing philosophical: What are the symptoms? How are we going to get this elegant lady to the ball?

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Ashe37 » Thu Mar 23, 2017 9:03 pm

Rasputin wrote:
Ashe37 wrote:And i got a dead vfx for parts for next to nothing and am now wondering if tis repairable
Everything is repairable in a sense, depending on your personal interpretation of the ship of Theseus paradox. Well, I guess that's not true if it's the only one left in the world and there are no parts to cannibalize and no way to recreate them.

But enough waxing philosophical: What are the symptoms? How are we going to get this elegant lady to the ball?

Well, I already have a working VFX... hence why it is parts.

I dont even remember if it is DOA or garbage in the screen, tis been in my storage for years.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Fri Mar 24, 2017 12:58 pm

Ashe37 wrote:Well, I already have a working VFX... hence why it is parts.
If you've already got it firmly slotted as a parts machine, I guess I'm confused as to why you were wondering if it could be resurrected as apparently you never intend to repair it even if it could be.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Fri Mar 24, 2017 6:34 pm

Floppy Drive Troubleshooting

First off, be sure you are using 720K/800K DD 3.5" disks, not the PC 1.44MB HD standard which will be the most commonly encountered style of floppy. If stuck with HD disks then put a small piece of electrical tape over the square hole (the one that doesn't have the write-protect slider). While not ideal, the VFX SD can work with disks modified in such a way, at least on a temporary basis.

If you are getting "Bad Device ID" or other errors while attempting read/write/format activity on multiple 720K disks then there is a significant chance either the floppy cable is bad or the floppy drive header pins are corroded. Clean the mainboard floppy connector header pins, and also the pins on the drive itself.

Due to the way most people remove ribbon cables, it is quite common for pins 1,2,3,4 and 31,32,33,34 to become damaged. If the floppy drive is not working properly although still powering up, use a multimeter to test continuity, especially on these pins.

Ensoniq VFX SD Floppy Pinout:

2 - Disk Change Detection
4 - Busy (In Use)
6 - N/C
8 - Index
10 - Device Select 0 (Drive A)
12 - N/C
14 - N/C
16 - Motor On
18 - Direction
20 - Step
22 - Write Data
24 - Write Enable
26 - Track 0
28 - Write Protect
30 - Read Data
32 - Side (Head Select)
34 - Ready

All odd numbered pins are grounds.

Drives need to be Shugart standard and the floppy cable needs to be a straight-through, not the traditional PC style with the ribbon drive swap twist built in. If a straight-through cable is unobtainable or if time is critical, the twist in a PC cable can be carefully undone to return the cable to a straight-through.

Note: The floppy cable in the VFX SD is longer than most other floppy cables, so aside from short-term testing purposes, an Ensoniq specific or custom made floppy cable is highly recommended for long-term part replacements. The form factor is also different from PC, so if using a modified PC drive then there will be a slight gap between the case and the floppy drive.

In the event that the floppy controller is bad, the good news is that they are relatively cheap and available. The bad news is that they are not socketed so will need to be carefully desoldered from the mainboard in the event of testing or replacement.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Ashe37 » Fri Mar 24, 2017 9:39 pm

be aware that HD disks will eventually bleed through and fail if used as DD disks for too long (i.e. too many rewrites)

cutoffres
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Re: Ensoniq VFX SD mainboard troubleshooting

Post by cutoffres » Fri Apr 28, 2017 4:23 pm

Replaced Q21 (79l05) (Q12 on vfx schematics) without success.
Tried to isolate some part of the -12V line without success, still have -9,18V on the -12V line.

Now there is even no light on the Disk Drive...

I'm a bit lost, i won't give up but maybe will try to troubleshoot with a second VFX sd if i'm able to find one?

Anyway thanks a lot for the help, i will post update if they exist :)

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Sat Apr 29, 2017 11:24 pm

cutoffres wrote:Replaced Q21 (79l05) (Q12 on vfx schematics) without success.
Tried to isolate some part of the -12V line without success, still have -9,18V on the -12V line.

Now there is even no light on the Disk Drive...

I'm a bit lost, i won't give up but maybe will try to troubleshoot with a second VFX sd if i'm able to find one?

Anyway thanks a lot for the help, i will post update if they exist :)
This might sound really... snotty, but I'm actually trying to be helpful :)

"Some part of the -12V line..." tells absolutely nothing. If you're using a divide-and-conquer approach to find a shorted part of the board or whatever the problem is then you have to go about it systematically. For example, if we disconnect the PSU from the mainboard then it's safe to say the -12V line with be at 0V, right?

My point is: Isolate part of the -12V circuit by cutting a trace or lifting a component leg, etc. If the voltage is still being pulled down then the isolated part of the circuit is not the culprit. Some component in the non-isolated branch of the circuit is at fault, so isolate more of the circuit. Not fixed? Well, you've just reduced the potential bad part search area from 100% of the mainboard to 25% of the mainboard.

I mean, that's an oversimplification of being able to divide the circuit in half perfectly, but you should be able to block off chunks by removing key components or cutting traces.

Look at the schematics and PCB to find a list of (easy?) ways to isolate sections of the -12V line on the mainboard. Make a list. Run down the list (make a note of what you've changed) and keep going until the -12V line returns properly to -12V as it correctly exists on the PSU.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Tue May 09, 2017 8:57 am

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!

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Ashe37 » Tue May 09, 2017 9:01 am

yeah sounds like the display.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Tue May 09, 2017 9:02 am

Obviously, the display... :lol:

The question is which way to go about it?
Could the display unit itself be dead? How can I make sure?
Would I need to hunt for a used keypad/display board on Syntaur, or could a replacement LED display do the trick?
Last edited by GiliRose on Tue May 09, 2017 9:07 am, edited 1 time in total.

Ashe37
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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Ashe37 » Tue May 09, 2017 9:06 am

the same display is used in a bunch of different ensoniq models from the era so at least you aren't replacing something model-specific

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by GiliRose » Tue May 09, 2017 9:10 am

Ashe37 - I just did a quick edit.
Is "just the display" a serviceable part?
I have yet to disassemble that board, so I haven't a clue what it looks like "underneath"

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