Ensoniq SQ1 - Corrupted Characters on Display

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Joined: Fri Oct 02, 2020 12:07 pm

Ensoniq SQ1 - Corrupted Characters on Display

Post by donnied » Mon Oct 05, 2020 10:58 am

Hi All,

My first post here, hence Big Hello to all.

I got this Synth for a song, for being broken. What is happening that SQ1 boots up normally sometimes, but sometimes the start-up also has funny characters on the screen, or boots ok, but after pressing a few times buttons on the panel, characters on the LCD screen again become corrupted with funny output from character set bank. Eventually, sometimes, display would go blank and you would get output on it if you press button "button #42" or whatever button ID is, keyboard still plays the last patch selected.

First thing I did was to recap all, and changed all regulators, bar 7812 and 7912 on the output. I have even changed LM2926T low dropout with delayed reset to be safe, as it was overheating badly. Got the thing a bit more stable, but it still was intermittent issue on boot or after some time. Also, was getting "Low battery" sometimes, even I put a new one in.

However, upon closer inspection, someone had a go at the main bard already and made some "interesting" mods.

1. Changed battery holder and burned the "+" track - Fixed now
2. Pads on 68681p for pin3 (IP1) and pin4 (RS3) burned/missing - Fixed now to relevant Via-s
3. Someone has an attempt to "fix" it previously and "joined" clock pins, pin1 (XTLO) and pin2 (XTLI) on 6500/11 - got me suspicious when comparing photos from the internet and that wasn't so

So to elaborate on 3. Removed the joint between p1 and p2 on 6500, and the thing will boot, but the no sound nor any control on the panel work, screen would show the first patch, and total freeze.

If during boot, any key (white or black) is pressed, it will boot and work, but after "abusing" and pressing too many keys on the control panel, it would freeze and play the last patch only.

This is where I got so far, I have ordered "logic probe pen", but it'll take a while to arrive from Hong Kong.

6500/11 P21, 22, 39 are all on Vcc
6500/11 P2 (XTLI) is connected to 74HC74 Pin5

P1 -> P4, P10, P13, P14 on Vcc
P2 -> P6
P3 -> ESP Pin1
P4 -> Vcc, see P1
P5 -> 6500 Pin2 (XTLI)
P6 -> P2
P7 -> GND, P11, P12
P8 -> NC
P9 -> NC
P10 -> see P1, Vcc
P11,12 -> GND
P13, 14 -> see P1, Vcc

6500/11 (inverted RST) Pin20 --> 68681 Pin34 (inverted RST) --> I could not trace what is keeping RST high on boot.

Questions so far:
1. Has anyone got a pinout of ESP chip, either 510000102 (or 510000105 in this case)
2. As I have changed LM319, what is the nominal voltage for ESP?
4. What is the clock frequency for 6500/11? 1MHz or 2MHz, or even 4MHz?
5. If 6500 in slave mode, I couldn't find any, but looks like XTLO is floated, is that correct?

Edit 2:
Forgot to mention
6500/11 P23 --> DISPOUT --> Display board direct link Connector Pin 6
68681 P11 --> SEROUT --> Display Board direct link Connector Pin 5

Many Thanks

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