Path: ...!news-out.netnews.com!postmaster.netnews.com!us7.netnews.com!not-for-mail
X-Trace: DXC=D1ZePNOSHgY2BFZQ=P]QnYU5[F2hIijD_7J470dMQQ7[J4R`5ADBYnR^blOYK0N2kR\lfPTGbeKk[Nfhi@Ij_EG]Uh:ZAVm]2iT1NI1l8fb?f^XlnNGcjcaFT
X-Complaints-To: support@frugalusenet.com
Date: Sat, 25 Jan 2025 20:16:07 -0500
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: Intermittent fault on Korg SDD 3300
Newsgroups: sci.electronics.repair
References: <67951f89$1$3620713$882e4bbb@reader.netnews.com>
 <absf6l-jreh1.ln1@coop.radagast.org>
Content-Language: en-US
From: bitrex <user@example.net>
In-Reply-To: <absf6l-jreh1.ln1@coop.radagast.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Antivirus: AVG (VPS 250125-4, 1/25/2025), Outbound message
X-Antivirus-Status: Clean
Lines: 47
Message-ID: <67958cd6$0$654094$882e4bbb@reader.netnews.com>
NNTP-Posting-Host: 127.0.0.1
X-Trace: 1737854166 reader.netnews.com 654094 127.0.0.1:60375
Bytes: 3466

On 1/25/2025 2:58 PM, Dave Platt wrote:
> In article <67951f89$1$3620713$882e4bbb@reader.netnews.com>,
> bitrex  <user@example.net> wrote:
> 
>> It's annoyingly unpredictable and seems somewhat related to how it's
>> mounted? I can power it up 25 times on the bench and it works fine
>> making me think I solved the problem, then slide it back in the rack and
>> it starts acting up again. I've tried a number of things like adding
>> bypass capacitance on the display board which is separated from the CPU
>> by good distance, disconnecting the backlight thinking it might be
>> interference from the inverter, moving the wiring around, also recapping
>> the PSU which I was planning on doing anyway. Doesn't seem to help.
>>
>> Here is the upper digital board (the analog board is on the lower
>> level), the lines to the LCD from the NEC Z80 variant are on the far right:
> 
> I'd be looking for things which could cause an intermittent connection
> on that cable and its connectors... maybe a bad or dirty pin or
> socket, maybe a hairline crack where one of the pins is soldered to
> the PCB.  A bad bus-driver on the main PCB (either a separate chip, or
> dedicated pins on the microprocessor) might have a similar effect.
> 
> If the characters being shown were characteristically off by one bit,
> it'd point to one of the data lines.  As it is, they seem to be
> rather unpredictably garbled, which suggests to me that one of the
> clock or handshaking lines might be bad.  Glitchy rising or falling
> edges on the "latch your data" signal might result in data being
> latched at the wrong time, while the data bus was in transition,
> and this could lead to all sorts of nonsense being displayed.
> 
> Might be worth pulling the cables, fluxing and re-flowing the
> connecting pins on the PCB, cleaning everything thoroughly.
> 
> If you have a DSO or logic analyzer which has a "look for glitch and
> runt pulses" acquisition feature, scoping the data and handshaking
> lines at the LCD while actively driving the display, and tapping on
> cables and the PCBs, might prove instructive.
> 
> 

Thanks for getting back, I'll follow up on those suggestions thank you! 
No logic analyzer available at home unfortunately but I have one I can 
probably use for a time if nothing else works..

-- 
This email has been checked for viruses by AVG antivirus software.
www.avg.com