OB-Xa - all EGs gone bad?
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Re: OB-Xa - unresponsive front panel/keyboard
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Last edited by Don T on Mon Feb 04, 2013 8:02 pm, edited 1 time in total.
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Re: OB-Xa - PSB issues
Finally got the new bridge rectifier installed after cleaning up the damage of removing the old rectifier, in order to rule out the common -5V bridge rectifier problem.
Still getting the "traffic cones" on the oscilloscope at the 5.5VAC and a non-responsive front panel. I would guess the next step is a recap?
Side note: I broke a pin on the keyboard ribbon cable, and had to order a replacement 16-pin ribbon connector.
Ideally, I would just buy a replacement power supply board, preferably with upgraded bridge rectifiers, to see if that solves the problem. Are early-rev and late-rev OB-Xa PSBs compatible?
Still getting the "traffic cones" on the oscilloscope at the 5.5VAC and a non-responsive front panel. I would guess the next step is a recap?
Side note: I broke a pin on the keyboard ribbon cable, and had to order a replacement 16-pin ribbon connector.
Ideally, I would just buy a replacement power supply board, preferably with upgraded bridge rectifiers, to see if that solves the problem. Are early-rev and late-rev OB-Xa PSBs compatible?
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Re: OB-Xa - power supply issues?
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Re: OB-Xa - power supply issues?
Can you post a pic of your schematic and mark the point where you are seeing that waveform?
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Re: OB-Xa - power supply issues?
What are the scale settings? How high are those peaks, in volts?
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Re: OB-Xa - power supply issues?
Can't really follow, but it was on the upper control board, after the connector to the power supply board, the joint right before the first resistor.Steve Jones wrote:Can you post a pic of your schematic and mark the point where you are seeing that waveform?
Can't really remember the scale settings on the oscilloscope.
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Re: OB-Xa - power supply issues?
Do you have a copy of the schematic? If you give me a connector number and pin where you are taking the reading (or a photo of the top board with the place marked) I will open one of my OBXa's and see what is there. Also are you making sure that you are earthing the oscilloscope probe correctly? The lead with the clip on the end that is attached to the probe should be connected to a ground point on the chassis when you are taking readings with the scope, that waveform looks like the scope probe might not be earthed correctly...
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Re: OB-Xa - power supply issues?
Connector K, pin 1 - what should be the 5.5 V AC according to the table in the service manual.Steve Jones wrote:Do you have a copy of the schematic? If you give me a connector number and pin where you are taking the reading (or a photo of the top board with the place marked) I will open one of my OBXa's and see what is there.
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Re: OB-Xa - power supply issues?
That trace on the 5V AC line is what you would expect to be there.
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Re: OB-Xa - power supply issues?
More observations:
- no matter how I tweaked the +15V, the -15V always read as -15.2V
- the 10K resistor to the right of the battery (the one that should be used to measure the CMOS current drain according to the service manual) - I got two measurements, one of over 100mV, but all subsequent measurements were zero.
- the Frequency and Pulse Width button lights are much dimmer than the rest
Which way should the switch on the motherboard be pointing - towards the back or front?
- no matter how I tweaked the +15V, the -15V always read as -15.2V
- the 10K resistor to the right of the battery (the one that should be used to measure the CMOS current drain according to the service manual) - I got two measurements, one of over 100mV, but all subsequent measurements were zero.
- the Frequency and Pulse Width button lights are much dimmer than the rest
Which way should the switch on the motherboard be pointing - towards the back or front?
Moog Matriarch
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Ensoniq Mirage/SQ-80
Roland JP-8/SH-101/RS-09/Kiwi-30
Korg MS-20 Kit/ARP Odyssey FSQ
Yamaha SY99/DX100
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Re: OB-Xa - power supply issues?
The mobo switch is just the memory protect on/off so it shouldn't matter. So have you measured all the PS voltages on all the boards? I've run into wiring issues between boards several times so you might do a continuity test on all the connectors...
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Re: OB-Xa - power supply issues?
How are you measuring the battery current?
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Re: OB-Xa - power supply issues?
I was following the service manual's instructions - measuring across the 10K resistor while the unit has been off for over five minutes.Steve Jones wrote:How are you measuring the battery current?
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Ensoniq Mirage/SQ-80
Roland JP-8/SH-101/RS-09/Kiwi-30
Korg MS-20 Kit/ARP Odyssey FSQ
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Re: OB-Xa - power supply issues?
Another observation: On the pot board, the +5.6V and -5V on IC 5 are instead fluctuating and unreadable. Reading it on the oscilloscope reveals a square/pulse wave. The connector that should be +5.6V between the pot boards is also displaying this square/pulse on the scope.
Can a problem on the pot boards freeze up the CPU or otherwise cause unresponsiveness?
The voltages on the control boards are good. Pin 16 of IC 145 on upper and 45 on lower are +5.55 (within the 0.2V tolerance of +5.6) and pin 7 of IC 149 on upper and 13 on lower are -10.34 (within the 1V tolerance of -10).
I had a feeling the pot board was fishy from the start...
Would it be
Can a problem on the pot boards freeze up the CPU or otherwise cause unresponsiveness?
The voltages on the control boards are good. Pin 16 of IC 145 on upper and 45 on lower are +5.55 (within the 0.2V tolerance of +5.6) and pin 7 of IC 149 on upper and 13 on lower are -10.34 (within the 1V tolerance of -10).
I had a feeling the pot board was fishy from the start...
Would it be
Moog Matriarch
Oberheim OB-8/DSX/DMX
Sequential Prophet 2002/Prophet-5 rev. 4
Ensoniq Mirage/SQ-80
Roland JP-8/SH-101/RS-09/Kiwi-30
Korg MS-20 Kit/ARP Odyssey FSQ
Yamaha SY99/DX100
Waldorf Microwave 1
Simmons SDSV
Elektron Analog RYTM
Oberheim OB-8/DSX/DMX
Sequential Prophet 2002/Prophet-5 rev. 4
Ensoniq Mirage/SQ-80
Roland JP-8/SH-101/RS-09/Kiwi-30
Korg MS-20 Kit/ARP Odyssey FSQ
Yamaha SY99/DX100
Waldorf Microwave 1
Simmons SDSV
Elektron Analog RYTM
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Re: Unresponsive OB-Xa - pot board issues?
Ah yes that would make sense since both control boards and the power supply I sent you worked fine in my Xa...
If you disconnect the pot boards are the voltages OK?
If you disconnect the pot boards are the voltages OK?
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