OK - This forum is closed for posting images and attachments, so explaining things gets kind of awkward. Rasputin - I am deducing from the link to the ESQ-1 display schematic that the suspicious elements might be the 1N34A diodes and/or the pair caps filtering each TL4810A. On testing, the 1N34A pai...

Hi Rasputin - You wouldn't happen to have a schematic of the display/keypad board, would you? I have a suspicion a few of the tiny Tantalum/Ceramic capacitors along the top of the board might be shorting to ground: C30, C27, C25, C24, C22, C10, C41 (unless a resistance of 0.3 ~ 0.5 Ohm is expected)....

Capacitor polarity is correct.
Unless a (-) with flowing white arrows stands for positive where you come from .

OK, I get you. You mean to actually isolate the filament from the PCB. I can eyeball the +9VAC trace from the connector all the way to pin 74 of the display (top left corner). Yes - it branches off via the central 10uF capacitor, then to a diode and some other stuff. The -9VAC trace goes direct from...

The forum login timed out on me so I will re-write this shortly: 1. The Cable is OK, all voltages are correct at the display end - while it is not connected. 2. Vbb is shorting out at on the display board. Resistance between the Vbb and GND pins is 0.00 Ohm. 3. Very possible short with the filament ...

OK - I follow the concept. Will test and report back.
I love the internet - thanks again Rasputin!!!

The Power Board is back in order! I aught to kick myself real hard too! Apparently I was sold the wrong R2 & R4 resistors, and out of natural trust, forgot to check. They were 22K and 360K - rather than the specified 22ohm and 360ohm. :banghead: OK, Vbb is back and chirping at 54.3 volts. The probl...

Could easily be a defective cap, especially one that you didn't replace. I have a pair of "under-spec" 50V 470uF caps I can replace (originals are 63V). I didn't replace them yet because of their lower rating. That might not be a problem, given that they need to handle 14-24 volt in the scheme of t...

You've reached a point where it is no longer Ensoniq specific, so you'll have to depend mostly on basic electrical system testing. At least until you get your 50V back on the PSU when it's unloaded. Replace anything bad and hopefully VBB will be correct again. If I had any hairs left, I would be pu...

I found the culprit! :dancer: Thanks Rasputin, your the man! It seems the previous owner suffered a short that burnt out Fuses F3 & F4 (the display board fuses). Wanting to get back to his music ASAP, he "repaired" the burnt fuses by wrapping a short length of wire on their exterior and stuck them b...

If you are totally sure you measured 50VDC on J3 pin 3 (aka point 21 in the service manual) previously ... No - I am not totaly sure. I am rather sure I overlooked this somehow. I actually can't recall seeing a 50v reading previously, so this was the dead spot from day 1 that I got the synth. The b...

I just checked the Vbb bus - it is OK all the way to J3 on the power board Sorry for the confusion. I meant the physical line of the Vbb starting from J3 on the power board, via the cable to the display board and all the way to the last component being "supplied" - is continuous, no breaks or funny...

I just checked the Vbb bus - it is OK all the way to J3 on the power board. HOWEVER - Pin 21 on the power board has the WRONG voltage - 1.6v !!! Wonder how I missed that the 1st time. With a magnifying glass I could see some component burn around R2 & R4 on the power board. Using the DMM set to resi...

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

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 gr...