[sdiy] SPV-355 -15V rail issue

Michael E Caloroso mec.forumreader at gmail.com
Sun Jun 18 18:19:55 CEST 2023


Make sure the tab on that LM7915 regulator has NO continuity to the
heatsink and chassis.  In my NS databook, the tab on the 79xx regulators is
tied to the INPUT pin - not COMMON.  Any second source suppliers will use
the same pinout.  This means you want NO electrical contact with the tab
and plate/heatsink/chassis.  The 79xx should have mica insulator between
the tab and mounting plate (with thermal conductive paste), and
non-conductive nylon washers on both the mounting screw head and nut, and
nylon tube insulators on the screw shaft.

ps the pinout for 79xx regulators in the 1989 TI Linear Circuits Vol 3
databook is WRONG.  Yes errors CAN appear in OEM databooks.

MC

On Sun, Jun 18, 2023 at 6:32 AM Adam (synthDIY) <synthdiy at adambaby.com>
wrote:

>
>
> On 18 Jun 2023, at 7:40 pm, Florian Anwander <fanwander at mnet-online.de>
> wrote:
>
> PS: there is a picture of the PCB at
> https://www.joness.com/gr300/pics/SPV-355/Roland_SPV-355_13.JPG but I
> could not find them (yet).
>
>
> Well at least that picture explains what Todd meant when he said "if the
> LM7915 is unplugged" - looks like the two regulators are on their own
> plugs, allowing a 'flying' attachment to some big heat sinks.
> Whatever is holding those heat sinks on may have shorted I guess... and
> they look like they're almost touching
>
> A
>
>
>
>
>
>
>
>
> Am 18.06.23 um 11:38 schrieb Florian Anwander:
>
> Though it is a shot in the mist:
>
> There are three types of tantalum capactors listed in the service manual.
> I bet those are on the supply rails and I bet (a little bit less) one of
> them got shorted.
>
> <kiJb1bnXjLNtD1VZ.png>
>
>
> Florian
>
> Am 16.06.23 um 19:12 schrieb Todd Sines via Synth-diy:
>
> I have an SPV-355 that was behaving adequately fine until recently. Unit
> will power on, (and LEDs illuminate correctly) if the -15V LM7915 is
> unplugged, when engaged, it shorts and blows both fuses.
>
> Wonder if anyone’s encountered this and if so, what did you do, or where
> did you look first?
>
>
> Todd
>
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