From Steve Lenham Sent Sun, Dec 23rd 2018, 10:37
From Steve Lenham Sent Sun, Dec 23rd 2018, 10:37
> Looking for help in debugging an Ensoniq Fizmo power issue... > Here's a high rez photo: > http://defectiverecords.com/temp/Fizmo-annotated.jpg > > Can anyone help in terms of next debugging steps, i.e. exact places to > measure voltages, or other suggestions? I'm hesitant to start probing > things without really knowing what I'm doing! (I'm competent in terms of > soldering and following basic instructions, but when it comes to > debugging circuits on my own, not so much). Hi Dan, Based on your photo, the circuitry looks quite straightforward (caveat: everything I suggest is based on that photo and not on personal experience). It looks like the pin and sleeve of the barrel connector each have their own ferrite bead/ceramic cap EMC filter. The filtered sleeve connection then becomes "ground" for everything else. The filtered pin connection goes through the power switch then on to two half-wave rectifiers (CR1 & CR?, just above the regulator). CR? (can't read it) feeds into the big electrolytic cap C11 and creates the unregulated positive input to your +5V regulator. CR1 feeds into the smaller SMD electrolytic C65 and creates an unregulated negative input to the -5V regulator VR3. So...if you take ground (middle pin of the 7805 regulator) as your reference, you should see: - 9Vac at the Anode of CR? and the Cathode of CR1 when the power switch is turned on, disappearing when the switch is turned off. - Somewhere around +10Vdc on the positive leg of C11. - Somewhere around -10Vdc on the negative leg of C65. - -5Vdc on the output pin of VR3 (the leg that connects to C79 & C74). - +5Vdc on the output pin of VR1 (top pin as viewed in the photo) - except we already know that you don't. Let us know what you observe and we can try to narrow it down further. The usual suspects would be the joints on the barrel jack, but the fact that the unit does something at all indicates that some power is getting in (always worth resoldering them anyway, though). A short circuit downstream of the 5V regulator is a possibility, but in that case I'd expect to still see some voltage at the input of the reg (this is good - you really don't want it to be that). Nothing like a bit of holiday debugging - at this stage, I'm backing CR? as the most likely culprit :-) Cheers, Steve L. Benden Sound Technology