samples playing backwards with occasional static burst

[alka]

Hello All,

I'm new to the forum but i have been visiting it often and have found it to be most helpful thus far in my quest to fix an Emulator II. When I received the unit it was powering on (with a whining transformer) but not booting. I have since then replaced the PSU, replaced the old display, fitted an hxc, reseated all ICs, and traced the non-booting issue to a dead 20Mhz crystal. It now boots reliably but I have an issue that I cannot seem to figure out. Hoping someone here can help!

The issue: Upon booting and after a bank is loaded the sounds of the bank are cycled (some play backwards) with each press of the keyboard ending the cycle with a large static burst crash. To hear what I am referring to click here: https://twitter.com/_alka/status/823963145760862210

All 4164 rams check out good and I've swapped about every IC on the digital board with no change in the behavior. It sounds like a micro controller issue but what do I know! Does anyone know anything about the PROMs at IC135 and IC137? Really hoping these are not the cause!! If so, can these be duplicated from a working machine at all?

I have run the debug program on a terminal and it says all ROM and Static RAM are fine, and I've done some disk and disk data tests but everything checks out fine and I'm not too certain what the other programs do...

Anyhow... hoping you all can point me in the right direction!!

[dr.c]

Before you start any attempt of diagnostics, you must choose a note to play with on the keyboard, and keep using always the same one.
You can eventually use different notes (keys) on the keyboard, but at least eight times each, and do not try to compare (yet) the G3 key and C3 key sounds, if you compare, it will be each same notes on the keyboard. Got it ?


First : what should be the original sound ? Just to compare the degradation.
An idiot came once and grabbed my head with a sound problem, and after an hour, he told me that big crack in the middle of the sample was normal, intended ! I tought I would kill him... So, now, I rather ask ! 
Use a pure and sustained sound, like flute or organ, not car crash samples 

Second : is it a sound coming from a diskette or did you sample it ?

Third : played still on the same note, is the  sound the same, with the degradation, or does it change randomly every time you press the key, (you must play this note at least eight times, in order to scan all the channels).
If, on the same note, the sound is the same, disable all channels except channel one and try. Is the degratadtion there ?
After then, disable channel one, enable channel two, and on the same note, is the sound the same ?
Same thing, till channel eight.

Let us know...

[alka]

Will do, sir... when i get home tonight. Unfortunately when I load in a bank and play just one key on the keyboard it cycles through all of the sounds within the bank even though only one sound is apparently selected according to the front panel... but I will get you the results of what you ask later on. Thank you for your help! 

[alka]

Ok... here are the results:

1. Loaded a flute bank in from hxc. after bank loads successfully. EII display shows one sound selected (the behavior is the same regardless of preset selected). Playing just one note on the keyboard results in all(?) sounds from the bank playing in succession with occasional burst. The burst does not coincide with any particular number of notes but it is cyclical - meaning i don't think it has anything to do with analog outputs. I get the same result throughout all channels 1-8.

2. The behavior is similar if I start with a just loading the OS and sample my own voice. The result with one note being played is that sometimes the sample is backwards, sometimes distorted, sometimes nothing. I have tested this behavior with loading the OS from floppy and hxc - exactly the same results.

memory address issues - microcontroller issues is what I'm thinking but I've carefully swapped each IC with new in-kind chips in these areas one at a time and nothing clears up the behavior. I cannot find any broken traces and all IC sockets that i've tested are fine. confused.

recorded some video here: https://mobile.twitter.com/_alka/status/825124881301905412/video/1

[alka]

Anyone? 

[dr.c]

Gimme a minute...   

[dr.c]

What is: OS from floppy and hxc - ?

[alka]

What is: OS from floppy and hxc - ?

I have replaced a failing drive with a gotek hxc SD card floppy emulator http://users.skynet.be/emxp/HXC.htm - erratic sample playback behavior is the same whether loading OS from 5.25" disk or SD card.

[alka]

Oh well.. Figures I'd buy an EII with an unknown and rare issue. I replaced the custom PROMs in the microcontroller today and the backwards sample/cycling through all the sounds in the bank issue did not change....

Is there anything on the Digital board that could potentially cause this??

[Wolfram]

Maybe you have a RAM problem.
Swap the first 4 RAM Chips withe the last 4.

[Elmbeatz]

Ok... here are the results:
...
recorded some video here: https://mobile.twitter.com/_alka/status/825124881301905412/video/1

I've never seen / experienced such behaviour...
But I'm sure it has nothing to do with loading a bank in particular (whether via HxC / Gotek  or original drive...)

[dr.c]

Excellent ! Your doc really speaks ! Congratulations !! If everyone could do like you ...
Now, is it the same by MIDI input from another keyboard ?

The sound Ram is as well o, a piggyback board ?

If yes, talke off that board, restart the machine, and see how it behaves.
If its the same, the piggyback ramm is okay. Just leave it somewhere, to put it back when the machine will work again.

If not, it means that there's a bad contact on the piggyback connector (check the pins), or a bad ram.

If its the same, swap half of the sound rams from the main bord with the other half of the main board. Is the problem the same ?

[alka]

Thanks Dr. C, same sound without Piggyback board, same whether played with the keyboard or external keyboard. I've given up on this one. Actually purchased another (with different problems) and I'm constructing one that actually works out of the two!

[dr.c]

Hi, its very late here, I'm dead. Coming back tomorrow...