Ensoniq VFX SD mainboard troubleshooting

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Werecow
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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Werecow » Sat Dec 03, 2016 10:45 pm

@Rasputin: Thanks for posting all that info! I like working mostly on Roland gear, but it's good to have those detailed operational notes available if I ever run across a dodgy Ensoniq that can't be escaped. ;)

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Sun Jan 01, 2017 1:38 pm

KEYPAD KEY MATRIX

Rows A-H correspond to diodes (CR1-8, respectively) while Columns are 6500 MPU pins 4-11. The 6500 MPU strobes the column pins (sequentially activating them) while monitoring the behavior of the rows.

8 rows * 8 columns = support for 64 possible switches.

It should be noted that the music keys are processed independently by a KPC MPU and not represented here. Also, keep in mind that there could be mistakes or typos. Sorting this list by either row or column will reveal any commonalities should a group of buttons exhibit incorrect behavior. For example, should pin 4 go bad then SW03, SW04, SW06, SW21, etc. will be non-functioning. Likewise, should CR1 go bad then SW01, SW02, SW03, SW36, etc. might be exhibiting masking or ghosting behavior, etc.

The bottom two pins of each switch are for the column, the top two pins are the row.

[A,08] SW01 = INC
[A,09] SW02 = DEC
[A,04] SW03 = S1 (soft button #1)
[C,04] SW04 = S2 (soft button #2)
[C,05] SW05 = S3 (soft button #3)
[B,04] SW06 = S4 (soft button #4)
[C,06] SW07 = S5 (soft button #5)
[C,07] SW08 = S6 (soft button #6)

[B,06] SW09 = CART
[B,07] SW10 = SNDS
[B,08] SW11 = PRES
[B,05] SW12 = SEQ BANK
[B,09] SW13 = 0
[B,10] SW14 = 1
[B,11] SW15 = 2
[C,08] SW16 = 3

[C,09] SW17 = 4
[C,10] SW18 = 5
[C,11] SW19 = 6
[D,05] SW20 = 7
[D,04] SW21 = 8
[G,11] SW22 = 9
[D,06] SW23 = VOL
[D,07] SW24 = PAN

[D,08] SW25 = TIMB
[G,06] SW26 = MSTR
[G,07] SW27 = STOR
[G,10] SW28 = MIDI CTL
[F,04] SW29 = LFO
[F,06] SW30 = ENV1
[F,08] SW31 = ENV2
[F,10] SW32 = ENV3

[D,09] SW33 = KANG
[D,10] SW34 = XPOS
[D,11] SW35 = RELS
[A,06] SW36 = SONG
[A,05] SW37 = SEQ
[A,07] SW38 = TRACK
[F,05] SW39 = PITCH
[F,07] SW40 = PMOD

[F,09] SW41 = FILT
[F,11] SW42 = OUT
[H,04] SW43 = PSEL
[H,05] SW44 = MIDI
[H,06] SW45 = EFCT
[H,10] SW46 = CLICK
[G,04] SW47 = MODE
[H,11] SW48 = LOCATE

[E,06] SW49 = WAVE
[E,08] SW50 = MOD MIX
[E,04] SW51 = PCTL
[E,09] SW52 = EFX
[H,07] SW53 = REPL PRG
[H,08] SW54 = MLTA
[H,09] SW55 = MLTB
[G,05] SW56 = REC

[G,08] SW57 = STOP/CONT
[G,09] SW58 = PLAY
[E,07] SW59 = SEL
[E,11] SW60 = COPY
[E,05] SW61 = WRT
[E,10] SW62 = CMP


Here is the list row-sorted (Note: Row A only has six switches as column 10 & 11 are not connected):


[A,04] SW03 = S1 (soft button #1)
[A,05] SW37 = SEQ
[A,06] SW36 = SONG
[A,07] SW38 = TRACK
[A,08] SW01 = INC
[A,09] SW02 = DEC
[A,10] N/C
[A,11] N/C

[B,04] SW06 = S4 (soft button #4)
[B,05] SW12 = SEQ BANK
[B,06] SW09 = CART
[B,07] SW10 = SNDS
[B,08] SW11 = PRES
[B,09] SW13 = 0
[B,10] SW14 = 1
[B,11] SW15 = 2

[C,04] SW04 = S2 (soft button #2)
[C,05] SW05 = S3 (soft button #3)
[C,06] SW07 = S5 (soft button #5)
[C,07] SW08 = S6 (soft button #6)
[C,08] SW16 = 3
[C,09] SW17 = 4
[C,10] SW18 = 5
[C,11] SW19 = 6

[D,04] SW21 = 8
[D,05] SW20 = 7
[D,06] SW23 = VOL
[D,07] SW24 = PAN
[D,08] SW25 = TIMB
[D,09] SW33 = KANG
[D,10] SW34 = XPOS
[D,11] SW35 = RELS

[E,04] SW51 = PCTL
[E,05] SW61 = WRT
[E,06] SW49 = WAVE
[E,07] SW59 = SEL
[E,08] SW50 = MOD MIX
[E,09] SW52 = EFX
[E,10] SW62 = CMP
[E,11] SW60 = COPY

[F,04] SW29 = LFO
[F,05] SW39 = PITCH
[F,06] SW30 = ENV1
[F,07] SW40 = PMOD
[F,09] SW41 = FILT
[F,08] SW31 = ENV2
[F,10] SW32 = ENV3
[F,11] SW42 = OUT

[G,04] SW47 = MODE
[G,05] SW56 = REC
[G,06] SW26 = MSTR
[G,07] SW27 = STOR
[G,08] SW57 = STOP/CONT
[G,09] SW58 = PLAY
[G,10] SW28 = MIDI CTL
[G,11] SW22 = 9

[H,04] SW43 = PSEL
[H,05] SW44 = MIDI
[H,06] SW45 = EFCT
[H,07] SW53 = REPL PRG
[H,08] SW54 = MLTA
[H,09] SW55 = MLTB
[H,10] SW46 = CLICK
[H,11] SW48 = LOCATE


Here is the list column-sorted (all this would be much better as a matrix diagram, of course):


[A,04] SW03 = S1 (soft button #1)
[B,04] SW06 = S4 (soft button #4)
[C,04] SW04 = S2 (soft button #2)
[D,04] SW21 = 8
[E,04] SW51 = PCTL
[F,04] SW29 = LFO
[G,04] SW47 = MODE
[H,04] SW43 = PSEL

[A,05] SW37 = SEQ
[B,05] SW12 = SEQ BANK
[C,05] SW05 = S3 (soft button #3)
[D,05] SW20 = 7
[E,05] SW61 = WRT
[F,05] SW39 = PITCH
[G,05] SW56 = REC
[H,05] SW44 = MIDI

[A,06] SW36 = SONG
[B,06] SW09 = CART
[C,06] SW07 = S5 (soft button #5)
[D,06] SW23 = VOL
[E,06] SW49 = WAVE
[F,06] SW30 = ENV1
[G,06] SW26 = MSTR
[H,06] SW45 = EFCT

[A,07] SW38 = TRACK
[B,07] SW10 = SNDS
[C,07] SW08 = S6 (soft button #6)
[D,07] SW24 = PAN
[E,07] SW59 = SEL
[F,07] SW40 = PMOD
[G,07] SW27 = STOR
[H,07] SW53 = REPL PRG

[A,08] SW01 = INC
[B,08] SW11 = PRES
[C,08] SW16 = 3
[D,08] SW25 = TIMB
[E,08] SW50 = MOD MIX
[F,08] SW31 = ENV2
[G,08] SW57 = STOP/CONT
[H,08] SW54 = MLTA

[A,09] SW02 = DEC
[B,09] SW13 = 0
[C,09] SW17 = 4
[D,09] SW33 = KANG
[E,09] SW52 = EFX
[F,09] SW41 = FILT
[G,09] SW58 = PLAY
[H,09] SW55 = MLTB

[A,10] N/C
[B,10] SW14 = 1
[C,10] SW18 = 5
[D,10] SW34 = XPOS
[E,10] SW62 = CMP
[F,10] SW32 = ENV3
[G,10] SW28 = MIDI CTL
[H,10] SW46 = CLICK

[A,11] N/C
[B,11] SW15 = 2
[C,11] SW19 = 6
[D,11] SW35 = RELS
[E,11] SW60 = COPY
[F,11] SW42 = OUT
[G,11] SW22 = 9
[H,11] SW48 = LOCATE

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Mon Jan 02, 2017 11:16 pm

Serial Communication Protocol & Handshaking

Note: This is solely reverse engineering and a work-in-progress. There's lots of guesswork involved, so any official or expert information (should it ever surface) should trump any musings rambled on about in this thread.

After a bit of investigative work, I've determined parts of the asynchronous serial communication protocol between the mainboard UART and the keypad/display MPU.

The mainboard talks to the display over a 62,500 (62.5K) baud connection with 1 start bit, 8 data bit, no parity bit, 1 stop bit (8N1) framing. The VFX can be talked to via computer using a 5V TTL level interface such as the ever-so-cheap FTDI 232R USB-TTL adapter and a terminal program such as RealTerm. The FTDI can be powered directly through USB but will need to be grounded separately -- the VFX heat sink works well for this.

To monitor traffic being sent by the CPU, connect pin 2 of the 4-pin display header (mainboard side) to the Rx of the USB-TTL adapter. Monitoring return Tx from the keypad/display board can be done via pin 19 of the mainboard keyboard header. A two-way link is not required, so it is possible to Tx or Rx to the display or UART in a one-sided manner. To send keypad data to the CPU, connect the USB-TTL Tx to pin 17 of the mainboard keyboard header. As the display protocol is not fully understood, it is not advisable to attempt sending serial traffic to the display.


Ensoniq VFX SD Mainboard UART Power-Up Serial Communication "Handshake"


The transmission begins with special commands of currently unknown meaning, but surely including display formatting such as screen/line blanking and cursor control: E7 FB FF FB F0 E7 FB FF FB F0 D6 7F 82 (in hex).

Next, the below text is sent via serial connection in plain-text ASCII to the display MPU:
CALIBRATING KEYBOARD - DO NOT TOUCH

After which, if the keyboard is not connected, or cannot be properly communicated with or calibrated then the following hex sequence and plain-text is sent:
FB FF FB FD FB FF FB F0 D6 7F 88 (hex)
KEYBOARD CALIBRATION ERROR (ASCII)
7F B7 (hex)
RECALIBRATE (ASCII)
7F C8 (hex)
IGNORE (ASCII)

If the display/keypad is able to communicate with the mainboard then the VFX will either stall on a keyboard calibration error or continue to display the welcome text and load the currently selected user interface soft menu in the event of a properly calibrated or intentionally bypassed keyboard.

Important Concept: One of the key things to note regarding this behavior is that the VFX does not need a display/keypad to boot the CPU. Even with a fully disconnected display, if the serial traffic is monitored then it is possible to know whether or not the CPU is booting as it will blindly transmit the keyboard calibration text to any listening device regardless of lack of response.


Ensoniq VFX SD Keypad/Display Power-Up Serial Communication "Handshake"


Upon power up, the display MPU attempts to send the following data to the KPC MPU and/or the mainboard:
FF F0 FF F0 FF FD <pause> FF F0

The final FF F0 seems to be broadcast after a period of getting no response from the KPC MPU but further research will be required.

It is currently unclear at which point in the handshake routine the MPU is able to register keypress data and transmit it to the mainboard. The 6500/11 will not Tx serial data while in self-test mode, so some Tx from the mainboard enables the 6500/11 to begin talking back to the mainboard. Also, it is unclear if the mainboard expects a serial response before the keyboard calibration is attempted, or only after.


Keypad Scancodes

It appears that one byte is transferred per keypress event. The most significant bit (MSB) of a keyup event is always 0 and the MSB of a keydown event is always 1, but the lowest 7 bits of each key remains the same.

It appears that it would be fairly easy (in the eye of the beholder, of course) to entirely replace the keypad/display with some modern and small programmable device in the event of a dead keypad/display PCB or fluorescent display, or to turn the VFX into a rack unit since the unit can operate without the music keyboard attached.

Here are (should I not be mistaken) the keydown scancodes in binary [simply change the first 1 to a 0 for keyup]:

Up: 10111100
Down: 10111101
Soft #1: 10111000
Soft #2: 10101000
Soft #3: 10101001
Soft #4: 10110000
Soft #5: 10101010
Soft #6: 10101011
Cart: 10110010
Sounds: 10110011
Presets: 10110100
Seq: 10110001
0: 10110101
1: 10110110
2: 10110111
3: 10101100
4: 10101101
5: 10101110
6: 10101111
7: 10100001
8: 10100000
9: 10010111

PERFORMANCE BUTTONS

Volume: 10100010
Pan: 10100011
Timbre: 10100100
KeyZone: 10100101
Transpose: 10100110
Release: 10100111
Patch Select: 10011000
MIDI: 10011001
Effects: 10011010
Replace Program: 10011011
Tracks 1-6: 10011100
Tracks 7-12: 10011101

SYSTEM BUTTONS

Master: 10010010
Storage: 10010011
MIDI Control: 10010110

SEQUENCER BUTTONS

Song: 10111010
Seq: 10111001
Track: 10111011
Clock: 10011110
Seq Control: 10010000
Locate: 10011111
Rec: 10010001
Stop/Cont: 10010100
Play: 10010101

PROGRAMMING BUTTONS

LFO: 10001000
Env1: 10001010
Env2: 10001100
Env3: 10001110
Pitch: 10001001
Pitch Mod: 10001011
Filters: 10001101
Output: 10001111
Wave: 10000010
Mod Mixer: 10000100
Program Control: 10000000
Effects: 10000101
Select Voice: 10000011
Copy: 10000111
Write: 10000001
Compare: 10000110

Special Notes About Scancodes

These are the scancodes as delivered directly by the 6500/11 keypad processor. As the scancodes loop through the KPC board they are altered in some partially unknown way (apparently transposing them by a value of 2 and appending one byte of additional code) and the mainboard will only recognize the scancodes as proper keypresses after they have been so modified. It is possible to bluff the mainboard into accepting a simulated keypad (via some external serial device) by offsetting each scancode downward by 2 and appending an extra byte of $00.

While using the keyboard jumper bypass trick, it is also possible to emulate certain keydown events without serial emulation by simply releasing the Program Control button after holding down particular buttons. The Program Control keyup event is then acting as a stand-in for the additional $00 byte, but the corresponding keydown event still needs to be offset by 2, so a button with a scancode lower than intended needs to be pressed. Confusing, right?
Last edited by Rasputin on Thu Mar 23, 2017 3:43 pm, edited 12 times in total.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by blueknob » Tue Jan 03, 2017 10:21 am

Blimy Rasputin.. that's a ton of info, do you ever leave the house? :lol: Actually...
The mainboard talks to the display over a 62,500 (62.5K) baud connection with 1 start bit, 8 data bit, no parity bit, 1 stop bit (8N1) framing. The VFX can be talked to via computer using a 5V TTL level interface such as the ever-so-cheap FTDI 232R USB-TTL adapter and a terminal program such as RealTerm.
I was having the display/key scanner chip die on my ESQ-1 a few years ago and I hooked up a RS232 board (with a slight mod) and from that I could both receive and transmit commands to the main board. It was quite good, it got messy with double buttons pressing plus there were some combinations I never knew of, but I managed to program up a PIC that did all the commands I needed.

It would be great if someone who worked on the design of this kit leaked the tech info ;) although I know that won't happen. I've worked in design labs myself, usually the info just gets lost in a company until it gets discarded. I have kept some tech info from some products I've designed but.. who cares? :lol:

Mr R, I would suggest do keep a log of your findings with the view of making a tech doc. I have and SD-1 and this info will be very handy should it start to misbehave. I already had to do major surgery on an EPS16+.

Great work.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by jxalex » Tue Jan 03, 2017 12:39 pm

Rasputin wrote:Serial Communication Protocol & Handshaking

The mainboard talks to the display over a 62,500 (62.5K) baud connection with 1 start bit, 8 data bit, no parity bit, 1 stop bit (8N1) framing. The VFX can be talked to via computer using a 5V TTL level interface such as the ever-so-cheap FTDI 232R USB-TTL adapter and a terminal program such as RealTerm.
Some questions: DOES the connection speed changes when it is in a normal mode or test mode?

SO, if to capture these keypad presses while you are in test mode, and so... to compare these keypad presses during normal mode, how it differs? Also when just trying to record these keypad data and send it from computer terminal... does it succeed while being in TEST mode? or also in normal mode? (i.e. keypad or keyboard presses from computer).
whoohh,, just a step away from MIDI retrofit...

Does the keypad scan generator changes its codes or is always the same and with the same speed wheter it is in test or normal mode?


the hardware hack is highly addictive activity and quite expensive too.
I noted that the SQ80 has these expensive CEM vca-vcf chips when I opened it today.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Tue Jan 03, 2017 2:27 pm

jxalex wrote:the hardware hack is highly addictive activity and quite expensive too.
I noted that the SQ80 has these expensive CEM vca-vcf chips when I opened it today.
Honestly, the VFX SD really has little reason to still exist as a hardware device aside from its use as a polyphonic aftertouch keyboard or just the hands-on, tactile interface. I say that because once all the program and waveform (Mega Piano, drums, et al.) ROMs are ripped then there is little reason why you can't digitally recreate the whole board. The Motorola CPU has no unobtainable mask ROM, and it's one of the most commonly emulated CPUs ever. MESS/MAME already has drivers for the ESP and OTIS chips, and in fact there's a virtual VFX (even if not fully complete) already floating around out in the ether somewhere.

My point is: I don't feel there's currently much that remains special about the VFX, whereas other legacy Ensoniq devices have CEMs and other ADC/DAC intricacies that makes the hardware still relevant. Even if SQ8L is really good, the ESQm still has analog filters, right? I feel the VFX series can/could be recreated in software to the degree it would be pointless to own, and without undue effort.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Tue Jan 03, 2017 2:38 pm

jxalex wrote: Some questions: DOES the connection speed changes when it is in a normal mode or test mode?

SO, if to capture these keypad presses while you are in test mode, and so... to compare these keypad presses during normal mode, how it differs? Also when just trying to record these keypad data and send it from computer terminal... does it succeed while being in TEST mode? or also in normal mode? (i.e. keypad or keyboard presses from computer).

Does the keypad scan generator changes its codes or is always the same and with the same speed wheter it is in test or normal mode?
Unsure.

As far as I can tell, the 6500 doesn't transmit serial data until it has received some type of configuration or startup data from the mainboard. I believe the CPU sends the 6500 a port configuration sequence upon boot which enables serial Tx from the keypad.

I believe the 6500 and UART are always at matching transmission clocks though, as the CPU wouldn't be able to bootstrap the 6500 into transmitting anything otherwise. A two-way handshake between the keypad and mainboard is not required, as the display will happily Rx anything from the mainboard without being able to Tx anything in return.

In other words, it's best to think of the display as Rx only, and the keypad as Tx only and those systems are basically independent although sharing the 6500. But (and it's a fairly big one) the mainboard Tx and display Rx have to work initially to bootstrap the keypad, even though (I'm still guessing here) once it is up and running I believe you could "fly blind" and operate the VFX without the display receiving any data from the mainboard. There is almost definitely no mainboard monitoring of its own transmissions. It seems to require no acknowledgement of its own Tx and doesn't require any kind of loopback, etc.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by cutoffres » Tue Jan 03, 2017 4:48 pm

Hi, i'm the subject opener.
I didn't except a so fast and complete response!
Sorry for the slow reaction. I'm now in front of the VFX SD, i've just replaced the CPU without succes on the fault.
I'm going to read all the details rasputin send and try to repair this vfx sd.
I would like to let know that the VFX and VFX SD have different pinout number.
I go now on the mainboard and will let know every successful or unsuccessful step.


EDIT: It has just booted one time and i see the screen with patch name for the first time! But not anymore. Now i'v got many differents SYTEM ERROR CODE:
SYSTEM ERROR 240 SYTEM ERROR 144 then SYSTEM ERROR 137 then SYSTEM ERROR 131 then SYSTEM ERROR 33

ERROR 240 Is not on the service manual, ERROR 144 is MIDI OR KEYBOAZRD ERROR OUT OF BUFFER, ERROR 137 is "line 1111 emulator" ????, ERROR 131 is "illegal instruction", ERROR 33 is "bad esp chip"

So to resume i'v got MIDI OR KEYBOARD and SOFTWARE and MAIN BOARD ERROR MESSAGE .
Maybe the only one ERROR message is right is the ERROR 33 "bad esp chip" a bad ESP chip would lead errors everywhere?

i've never been so happy to see an ERROR CODE :lol: but still not booting correctly of course.
Continue to investigate mainly on the ESP CHIP that coulbe the culprit?
Last edited by cutoffres on Tue Jan 03, 2017 6:41 pm, edited 1 time in total.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Tue Jan 03, 2017 6:37 pm

cutoffres wrote:EDIT: It has just booted one time and i see the screen with patch name for the first time! But not anymore. Now i'v got many differents SYTEM ERROR CODE:
SYSTEM ERROR 240 SYTEM ERROR 144 then SYSTEM ERROR 137 then SYSTEM ERROR 131 then SYSTEM ERROR 33

ERROR 240 Is not on the service manual, ERROR 144 is MIDI OR KEYBOAZRD ERROR OUT OF BUFFER, ERROR 137 is "line 1111 emulator" ????, ERROR 131 is "illegal instruction", ERROR 33 is "bad esp chip"

So to resume i'v got MIDI OR KEYBOARD and SOFTWARE and MAIN BOARD ERROR MESSAGE .
Maybe the only one ERROR message is right is the ERROR 33 "bad esp chip" a bad ESP chip would lead errors everywhere?

i've never been so happy to see an ERROR CODE :lol: but still not booting correctly of course.
Continue to investigate mainly on the ESP CHIP that coulbe the culprit?
My guess would be the power supply. I wouldn't trust any of those errors to be a genuine error, but more indicative that the CPU is going bonkers. Before you try to do any other kind of troubleshooting, check, check, and recheck the condition of the power coming off the PSU, especially for ripple on the 5V digital line. If you're 100% sure it's good then maybe look at the decoupling capacitors on the CPU / RAM / ROM.

If you were asking if the VFX and VFX SD have the exact same pinout / schematics then the answer is "No." BUT, they are very close. The VFX/VFX SD/SD-1 are all revisions of the same thing and so there are a couple extra lines added for the floppy disk controller, etc. but in the majority of cases any troubleshooting info can be substituted for any of the models.

If it powers up consistently but keeps throwing ERROR codes, try booting without the keyboard & keyboard cable attached to the mainboard at all, and see if it reboots or does anything strange if you just let it sit at the "CALIBRATION FAILED" screen forever.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by cutoffres » Wed Jan 25, 2017 7:21 pm

I have Triple checked the Power supply:

It has a WRONG VRES and a WRONG -12V ANALOG when the mainboard is connected to the power supply (0.32V for VRES and -0.62V for -12ANALOG)

When check the Power supply unloaded (not connected to any other board) it has a RIGHT VRES (4.90V) and a bizarre and out of spec -12 ANALOG (measure instable voltage that goes from -10.10V to -7.50V then stabilize to -9.88V)

So i have a faulty power supply and a faulty mainboard.
Going to search for the -12 ANALOG fault on the power supply then i will investigate for the faulty VRES and -12V ANALOG on the mainboard.
Will let know any advancement, but Any idea is still welcome.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Thu Jan 26, 2017 12:06 am

cutoffres wrote:So i have a faulty power supply and a faulty mainboard.
Going to search for the -12 ANALOG fault on the power supply then i will investigate for the faulty VRES and -12V ANALOG on the mainboard.
Don't be so sure that you have a faulty mainboard just because the PSU measures differently when under load. While it's true that it could be faulty, if the PSU is bad then it can measure faulty not only unloaded but even under a proper load (i.e. when the mainboard is working correctly) too.

Fix the PSU 100% and then restart your troubleshooting from scratch.

In other words, if the rectifier diodes or filter caps are gone in the power supply then a digital multimeter isn't going to give you real measurements because the DC voltage will be so full of sawtooth waves and/or ripple that it can't measure with any degree of accuracy. It'll average out what it's seeing, but that won't be very close to what is really going on. You need to find out why the voltage is bad first. The first thing I would do is to check the large filter capacitor just before the 7912 regulator. I think it's C14 @ 3300uF but your power supply might be slightly different.

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Re: Ensoniq VFX SD mainboard troubleshooting

Post by cutoffres » Tue Feb 07, 2017 6:27 pm

Ok, replaced burned fuses :? :oops:
Checked the Power supply 10 times, then replaced the -12 regulator (7912) that was dead.

Now when the Power supply is unloaded all the voltage are correct apart from
+VU that is 12,43V (allowable range is 8 to 11V on the service manual) and
DISPLAY OFFSET that is 13,06V (allowable range is 8 to 11V on the service manual)

BUT when i plug all the boards to the Power supply board, all the voltages are correct except the VRES voltage that is: 0,02V .

( that is why i suspect the power supply board to be now giving the correct voltages) I think this voltage are good for an unloaded power supply board, because the service manual ask to measure this voltage with all the board pluged to the power supply board then indicate to disconnect boards one by one, if the mesured voltage are wrong. Do you see what i mean?

So my question is: should i continue to replace parts on the power supply to get the proper +VU and DISPLAY OFFSET voltage when unloaded?
or
We can state that the power supply is now good (good voltage when loade except for the VRES) and try to troobleshooting the VRES voltages ?

Thank you

Rasputin
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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Tue Feb 07, 2017 8:27 pm

cutoffres wrote:We can state that the power supply is now good (good voltage when loade except for the VRES) and try to troobleshooting the VRES voltages ?
The lines you said were too high are unregulated on the PSU and one gets regulated later on the KPC PCB, so it's probably not an immediate worry, at any rate. Glad you fixed the analog voltage!

The VRES is controlled by LM2926 and is totally critical for the CPU to boot, so if it's always stuck at almost 0V then there's a problem. That should be your key focus now, yes.

That's going to be a bit tricky. They are designed to drop the reset line if anything "bad" is going on. So the LM2926 could be bad, but it could also be stuck in protection mode because there's a short, it's overheated, it's overvolted, or it's getting wonky power.

There's also a capacitor tied to the LM2926 that controls how long it takes for the LM2926 to start operating again once the fault is cleared (no more short circuit, etc.) Usually this delay is only around 32-48ms, but if the capacitor can't either discharge or charge then the LM2926 VRES won't work as designed. There are multiple reasons why the delay cap needs to work, but one of primary interest to us is that the capacitor not only controls fault delay but also POWER-ON delay. Pin 4 on the LM2926 should lead to a low-value capacitor (C21, probably). That's the fault delay cap. I'd check that first as it's like $0.02 to replace.

Hopefully it's not the LM2926 as they're bordering on rare and a bit $$$, although certainly not impossible to obtain.

cutoffres
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Re: Ensoniq VFX SD mainboard troubleshooting

Post by cutoffres » Wed Feb 08, 2017 4:24 pm

You're indicating a paussible fault of "LM2926 and associate capacitor" that are located on the power supply.

But all the voltage are good when the Mainboard is unpluged from the power supply board
A) For me that mean that i should invinstigate on the mainboard and not on the power supply? Could you confirm or infirm that?

Rasputin
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Re: Ensoniq VFX SD mainboard troubleshooting

Post by Rasputin » Wed Feb 08, 2017 4:44 pm

cutoffres wrote:But all the voltage are good when the Mainboard is unpluged from the power supply board
Are they though? If VRES isn't 5V then how is it good? Rhetorical questions.

Yes, look at the PSU as that's where the RESET line is generated.

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