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Yamaha HS80M Problem with switch on input PCB
Yamaha HS80M Problem with switch on input PCB
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Old 3rd January 2018, 11:48 AM   #1
PhantomBox is offline PhantomBox  Venezuela
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Default Yamaha HS80M Problem with switch on input PCB

Happy New Year to all!

I have a Yamaha HS80M monitor that turns on but makes no sound until I move the ROOM CONTROL switch (S2 on the input PCB) back and forth. After a few wiggles (with popping sound each time the switch changes position), it turns on.
I took out the input PCB and injected some isopropyl alcohol inside this switch and wiggled it but the problem is still there.
I do have the schematics. There is a network of resistors and caps and an op-amp associated with this switch. The problem is that it is all SMD.

I was going to remove the switch S2 (3 position selector, 5 pin) for disassembling and cleaning but after checking it out with a magnifying glass I had second thoughts...

Any ideas? Anyone having similar problems with this monitor?

Phantombox

PS: I forgot to mention that these monitors are working in a somehow damp environment, all metal parts (speaker casings and brackets on circuit boards but not the PCBs) show signs of moisture.
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Old 3rd January 2018, 01:35 PM   #2
Mooly is offline Mooly  United Kingdom
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Yamaha HS80M Problem with switch on input PCB
Have you resoldered the switch to eliminate the possibility of dry joints ?
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Old 3rd January 2018, 05:32 PM   #3
PhantomBox is offline PhantomBox  Venezuela
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Just resoldered the joints on the switch.
Doesn't fix the problem. Now, when wiggling the switch to fast the speaker turns itself off and I have to move the power switch off and then on again.
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Old 3rd January 2018, 07:30 PM   #4
Mooly is offline Mooly  United Kingdom
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Yamaha HS80M Problem with switch on input PCB
The joints had to be looked at...

I think the only sure fire to attack this now is to follow normal fault finding procedure which means applying a known signal and tracing it through with an oscilloscope.

Is moving the switch really 'fixing' the issue, or is it a red herring as they say. You need to trace the signal and see where it goes astray.
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Old 4th January 2018, 12:15 AM   #5
PhantomBox is offline PhantomBox  Venezuela
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Hello Mooly.

I got the monitor working again, using the "red herring" way.
Unfortunately my oscilloscope is not working and I haven't found someone to fix it. I do have access to another one that works with a laptop via an interface, but the guy who owns it is on holiday.
This may take a few days...
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Old 4th January 2018, 12:52 AM   #6
turk 182 is offline turk 182  Canada
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signal tracing doesn't require an oscilloscope my old Eico 147 does a great job at letting me know where signal is or isn't! (or any medium gain amp like an lm358 can work as a "tracer" in a line level circuit) and the thing i like about it is i don't have to look away from what i'm doing (reducing slip ups)i can hear where things get lost.
or injecting signal from the output amp and working back through to the input should help narrow down the section with the fault.
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Old 4th January 2018, 01:30 AM   #7
PhantomBox is offline PhantomBox  Venezuela
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Hi Turk.
Those good old days... Unfortunately I don't have one of those tube loaded EICO tracers.
I guess I could just use any guitar amp: unbalanced cable plugged to the amp and the other end instead of a guitar I would connect ground of cable to ground of monitor and tip with a wire as my "tracer"...
Would this actually work?
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Old 4th January 2018, 01:50 AM   #8
turk 182 is offline turk 182  Canada
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you don't need some thing as hi gain as a guitar amp, any line level amp you have (think old stereo amp) make a probe with an old RCA cable with an alligator clip for ground and and old meter probe to the signal line and your in business. in the "old days" i would bypass the rf section of a portable transistor radio for a signal tracer.

Last edited by turk 182; 4th January 2018 at 01:55 AM.
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Old 4th January 2018, 01:02 PM   #9
PhantomBox is offline PhantomBox  Venezuela
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I have something like this. I'll give it a try.
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Old 5th January 2018, 05:36 PM   #10
PhantomBox is offline PhantomBox  Venezuela
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I kinda narrowed it down.
When disconnecting the input pcb, there are +14.85V and - 13.75V on the pins coming out of the power pcb. When I connect the input pcb back there are +14.85 and -0.8V on the pins, so the problem should be on the -V power on the input pcb.
I can "jumpstart" the monitor and then the voltages are ok (well, +14.85 and -13.75 is not optimal but it doesn't induce any noticeable noise).
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