Stuck diagnosing Roland JV-30 synth - powers up with no display - any ideas? - Page 1
Forum section: electronics / repair

author: bobby4star
author_rank: Newbie
timestamp: April 06, 2019, 07:48:41 am
content: Hi all,I am trying to repair a Roland jv30 synthesizer, it is a nice synth in good condition and would be great if I can repair this!The synth powers up when the 9 volt DC power is applied, the display backlight lights up but no characters are displayed, the top row chars are just very faintly showing blocks. No sound, no button leds or any other signs of life!The first thing I checked was the power supply section. The incoming 9 volt rail is up, the diode D5 is ok and the plus 5 volt rail is up. The plus and minus 12 rails are not running at 12 volts. The plus 12 volt rail at the output of IC 26 is showing about 6.8 volts and the output of IC 27 is showing 0v. The +/- 12 circuit is controlled by various transistors, diodes and capacitors, I have to say I cannot quite follow how that circuit is working, beyond the fact that it is controlled by some input logic with and gates in IC 29 and an incoming pulse. Checking the state of the inputs outputs of the and logic gate the output of that section is low which I suppose is causing the12volt rails to be down.So my thoughts were that perhaps the CPU is not initializing the code. Looking at the test points around the CPU I can see a nice wave from the crystal oscillator the system clock is running and I can see pulses on the data bus and address buses. The X reset line was high but I did wonder if this was working correctly so I swapped out the 5 volt regulator IC 78MR05. Using my newly acquired oscilloscope I could see that the X reset line has the correct expected delay and comes up just slightly after the 5 volt Rail when the charging cap is ramped up.So having checked all these things I'm at a bit of a loss as to what is wrong with this board I have in desperation run my soldering iron across the pins of all the ICS and also across the many via's on the board. This has not made any change and the broad still does not boot. I've then further checked all of the SMD chip capacitors for shorts just using my multimeter on diode mode and also using my ESR meter but I don't think that it really is up to the job for these tiny smds.So I am at a bit of a loss as to where to go next with this board and any suggestions are most welcome! I have attached photos of the board and circuit diagram power section and hopefully I can upload the whole document.I am really hoping that someone has experienced this problem before and has identified the cause.All the best, Bob

author: pbarton
author_rank: Frequent Contributor
timestamp: April 06, 2019, 11:47:49 am
content: Re: "IC 29...Checking the state of the inputs outputs of the and logic gate the output of that section is low"Pin 1 needs to be high to enable the +12V and -12V supplies.So, you need to go further back in the diagram to determine why pin 1 is 0V.Apparently this leads back to Hitachi H8/532 processor Port 9-0/FTOA2Devices that contain a microprocessor frequently run a diagnostic routine, before being ready.Typically these routines verify that the microprocessor, clock, ram/rom memory and possibly other peripheral chips, are all OK.If the microprocessor detects an error, it may not get as far as sending characters to the display or enabling the +12V and -12V supplies/regulators.Without an error code or any LED readout or flash code, it may be difficult to determine the nature of the problem.No bleeps from a buzzer? No buzzer on the board?Even if you had an error code, if the manufacturer has not published what the codes mean, then you are stuck.Owners Manual and Service Noteshttps://www.synthxl.com/roland-jv-30/