[KL] Midiboard v3 error13

[[e-mail] [KurzList]]

Hi all. I bought a defective Kurzweil Midiboard V3, Japan built. Is boots with an error 13.


I have been reading some posts with the notorious error 13. My technician is working on it but the error keeps coming. AD converter and capacitors have been replaced, one was already leaking (next to the AD). Connectors were cleaned as well. This is what my technician says:


"The 100 kHz signal is present. In testmode 1, the sliders and wheels do not react so it isn't possible to read out any values while moving slider A (as mentioned in the troubleshooting). U21 reads a high signal at pin 1."


Do you guys have some tips for me to check? Thanks in advance!
JP


Picture of the leaking capacitor: https://1drv.ms/u/s!AqMbkemveqKPtHBT4488uxMKFapk https://1drv.ms/u/s!AqMbkemveqKPtHBT4488uxMKFapk

[[e-mail] [KurzList]]

Do the keys respond in the test mode?

Does the DAC output anything? If so, does this serial train of slots of analog values appear to change with controls or keys?


All keys and controls are analog, serially multiplexed. The serial stream starts with the 100KHz and is divided into slots for each devices proper timing. All can be observed. Every thing is analog except the simple timing of the slots until it eventual is feed to the DAC. Each item can be viewed in this serial stream to the DAC too.. The DAC cleans up the timing and digitizes to feed the data to the micro processor. You processor running and therefore good, leave alone. If nothing is going into the DAC, look earlier at the simple devices that create the serial stream. Any slot hard up or down needs checking.


Do you see a any UP DOWN messages if you hold down some keys during power up? This would be normal.


Do you have the draft and never finalized horrid service manual to help understanding how this all works?


Usual people attempting repairs jump to the wrong conclusion, then change good parts in desperation, often making a simple repair worse.

[[e-mail] [KurzList]]

Thank you for your reply, much appreciated! I will let my technician look at it and come back to it soon.

[[e-mail] [KurzList]]

@winking_n_nodding: The DAC outputs everything except wheels and sliders. According tot the manual IC U2 (R6522) needs to be replaced in this case. Do you think this is the right conclusion?



Image of board with IC U2 at the right: https://1drv.ms/u/s!AqMbkemveqKPtGO9M9otEtMNKm3S https://1drv.ms/u/s!AqMbkemveqKPtGO9M9otEtMNKm3S


Image of schedual with IC U2 at the left: https://1drv.ms/u/s!AqMbkemveqKPu1dzFcjApfdfHheA https://1drv.ms/u/s!AqMbkemveqKPu1dzFcjApfdfHheA


Hope to hear, thanks!

[[e-mail] [KurzList]]

I am away from home and do not have a midi board schematic at hand to examine this as a possibility.

After having done a lot of Logic Board repairs on Midi Boards, EGs and EG2s, I have never seen the 6522 fail. I an NOT saying that it is not possible. I am saying that if I was working on it, I would exhaust the other possibilities first. I could be totally wrong and maybe the 6522 is bad, but my past experience say caution on any service manual conclusions.


All the manuals from that time were done by subjective deduction, not objective experience, These technical writers were not bench technicians. In theory, they were possibly correct, but in the real world, rarely correct. They will get to an area, not a component.


It always turned out to be the smaller items that multiplex a group of 8 or the timing of those 8 to 1 multiplexer.



I will examine the circuit later this week, after I return from my trip and reply.

[[e-mail] [KurzList]]

Thanks winking_n_nodding for taking the time to look at the schematics, much appreciated!

Regards,
JP

[[e-mail] [KurzList]]

Did you find some time already to take at look at it winking_n_nodding?


Thanks,
JP

[[e-mail] [KurzList]]

JP,

Looking at your picture, I'm hoping that the AD converter you replaced is that U16 (ADC0820CCN) chip. There appears to be a lot of damage to the surrounding solder pads, looking at the resistor array R101.

More concerning is what appear to be metal tendrils (tin whiskers) emanating from the pads of the yellow choke and C30, and to some extent U16. That board needs a physical cleaning with pressurized 91% isopropyl alcohol (use one of those 1-qt. hand-pump sprayers you get from the local garden center) or can of circuit board cleaner (freon), using a soft-bristled toothbrush all around these components, then flush with the alcohol/freon.

Once the board is nice and clean, go over all the discolored solder pads with a touch of fresh solder.

[[e-mail] [KurzList]]

It was indeed U16 that was replaced. The board was also well cleaned, but we will inspect it again. Thanks for the tip!