Roland Jupiter 8 data bus problem need help

[Joseph Redhemption]

Hi to all,

I have a faulty jupiter 8 (12 bit version) on my bench and trying to repair it without sucess.

Description of problem :
When power up  -> weird display and nothing working. No sound and no effect when pressing any knob.

First did check PSU and all voltage ok and didnt see anything wrong with scope.
Then looked around Z80 cpu to find any problems.
What I got so far is that the data bus D0-D7 after buffer IC15  doesnt seems right.
D0,D2,D5,D6 are nearly at zero, not like when a gate is pulled down but more like it has some hash on it with small spikes of 1v.
D1,D3,D4,D7 are looking good with solid logic levels.
I was thinking that one of the IC on the data bus is making a mess because the data D0 toD7 of the z80 looked OK.
First I changed data buss buffer IC15 on CPU BOARD without succes same symptoms.

So I unplugged the PANEL A connector AI from INTERFACE BOARD and the bad data lines where nearly ok. The signals are not like a solid square but with a ramp on rising edges.  Ramp duration 1us from 0V up to 2V then solid square.

This makes me think 2 possibilities
1 - its normal and faulty IC must be on PANEL A
2 - Its not normal and maybe another IC is messing up the data lines.

So I started with possibility 1.
I replaced all IC on data line of PANEL A BOARD. Replaced IC8,9,10,11,12,13,14,15,16
but without succes data line still messed up.

I'm thinking now of replacing the IC's on the data buss on the INTERFACE BOARD .
They are : IC5,7,10,11,13,16,18,19
But before I do that I tried to cut the pin D0 of each IC of INTERFACE BOARD on data buss to see if it brings back the data on this line. This could have helped me to spot the bad IC.
It didnt change anything on data line D0. Still at some kind of zero with spikes.
Does this mean that if I replace all of the above mentioned IC's it wouldnt solve the problem?

Is there anywhere else to look at?

Any help apreciated.

 

[Joseph Redhemption]

Up

 

[zamproject]

Hello Joseph

I'm not a digital expert, i'm sure some pple can help you here .
BUT you talk about 20 IC, diode, and CPU ?!?
WITHOUT any schematic !!!
How are we supposed to understand what you are talking about?

for the "general" things to look at... the 30+ years old electrolytic capacitor (I have bad experience with them in a juno60) also the battery.

By the way welcome to the board.
Zam

 

[Andy Peters]

For starters, a schematic will help. You make references to ICs as if we all have the schematics available and can tell you what these parts are supposed to do.

I assume that you checked the power supplies with a proper voltmeter.

I assume that you have a 'scope fast enough to look at digital signals.

Have you looked at the processor's clock to make sure it's toggling at the correct frequency? Monitor the reset line with the 'scope to make sure the processor is actually reset, and that the reset is deasserted in a reasonable manner?

Connect a logic analyzer to the processor and monitor the data and address buses and control signals. Make sure the address isn't stuck somewhere.

Shotgunning parts is a waste of time and money.

 

[kazper]

http://manuals.fdiskc.com/flat/Roland%20Jupiter-8%20Service%20Maunal.pdf

 

[Patrick909]

Up

Interested to find out what the diagnosis was for this one?