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daigs
Member
Last Activity: 09-05-2023, 09:45 AM
Joined: 11-15-2022
Location: rome
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Re: Yamaha P-115 turn on but No sound - Doesn't turn off
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Re: Yamaha P-115 turn on but No sound - Doesn't turn off
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Yamaha P-115 turn on but No sound - Doesn't turn off
Hi,
I need to repair a P-115 yamaha digital piano with a strange behaviour.
When I power on the piano from the dedicated on/off switch, the power led go to ON (red led), but the keyboard doesn't produce any sound, nor in the speakers nor in the headphones.
When I try to power off (pressing the switch for at least 1 second), the keyboard doesn't power off, the red led remains ON. I need to unplug the adapter cable to switch off the keyboard.
I checked the 12V voltage rail on the input PCB, after the power plug and it is OK.
I checked also the... -
Fender Blues Junior IV guitar amp not working
Hi,
I need to repair the guitar amp in the title. I'm new on tubes, it's the first time for me. Usually I repair keyboards.
After a time from 10 to 25 seconds about from power-on, the amp start randomly with one of the following issue:
-some intermittent little pop/cracking sounds on the speaker followed by a “uuuuuhmmmmm” continue sound
-a continue big big distorsion sound, like a big noise (with the volume and master to zero, see the video)
Yesterday I powered on the amp and all went well without crack sounds and with no audio distorsion for about 30 minutes.... -
Re: Guitar Amp Marshall 75 reverb issue
OK the Ampli work well with the new TR.
Now I have to change it with an equivalent BD370D. Any suggestion is appreciated.
Regards.Leave a comment:
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Re: Guitar Amp Marshall 75 reverb issue
Ok, I will try.
What could be a correct replacement of BD370D?Leave a comment:
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Re: Guitar Amp Marshall 75 reverb issue
Hard to find the BD370D BJT... I not even found a just match/equivalent online.
I found in a old laboratory a new BD370C that differ for the max collector emitter/base voltage. The "C" is 80V while the "D" is 100V.
In our opinion can I mount the "C"?Leave a comment:
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Re: Guitar Amp Marshall 75 reverb issue
Thanks budwich.
Some news here.
I powered up the amp with TR12 and TR13 disconnected. The -45V DC still present at the base trace of both TR12 and TR13 and some other points connected!
At the speaker output a voltage of about 9.5 V DC that after some seconds were 9.4, after 5 seconds 9.3... and so on.
Going backwards in the circuit I measured again TR7 (it was already measured at the first check) and noticed that the base emitter junction was open. I took out it from the circuit and all...Leave a comment:
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Re: Guitar Amp Marshall 75 reverb issue
Can someone say me the .33 on R67 and R68 what mean? What value should I expect?Leave a comment:
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Re: Guitar Amp Marshall 75 reverb issue
I confirm that I measure -45 volt DC between the 0 volt rail and the node between R67 and R68. The same absolute 45 V DC is measured between the speaker outptut.
TR12 and TR13 seem good measured with the multimeter!
Regards.Leave a comment:
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Re: Guitar Amp Marshall 75 reverb issue
Lots of useful information, I appreciate that.
Devil_Rider, the sound is not a typical DC bump on the speaker, but as you said is more a sound like a ground but not a true ground sound. The "oscillation" cause you suggested could be true. Can you please explain me what stage I have short to ground with the cap, with reference to the schematic?
R_J I checked the R67 and R68 and to me they both measure 1.8 ohm each at my not professional multimeter (0.8 ohm is the internal probe resistance). I don't understand...Leave a comment:
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Re: Guitar Amp Marshall 75 reverb issue
Thank you for your answers.
The measured voltages are after the capacitors and rectifier. Remember that we a have a mono amp stage here, not stereo.
Devil Rider, I changed only C48 and C49 capacitors. How this oscillation you are talking are created by the circuit? Can a filter cap (e.g. C40) causes the main rail voltage 45V to be across the speaker output?
The 45 DC volts are measured between the output wires speaker. There isn't a true ground but a +V 0 and -V.
Two extra questions:...Leave a comment:
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Guitar Amp Marshall 75 reverb issue
Hi there, new fault hardware over my desk.
I'm talking of a Marshall Guitar Amp 75 Reverb.
Turning on the amp a "uuummmm" high level noise come out from the speaker. If I connect a source at the input nothing change.
Attached you can find the schematic.
I checked all the +/- voltages, 15, 24 and 45 and all are OK. The input fuse is not burned.
With the speaker connected or disconnected the R44 R45 R46 R47 are soon (10 seconds) very hot.
With the speaker disconnected I measure 45 volt DC on the speaker output terminals.... -
Re: Yamaha Tyros strange keys issue
After cutting several paths on the PCB and measuring the resistance, turns out that some vias were oxided. That oxide had produced a pseudo-layer of partial conductive material between signal and ground, creating a no stable recognition by the scanner. At the same time the ground layer near to the vias was oxided too and the copper was starting to lose the solder mask.
Now all is OK.
I hope that fix will last for some time, because some vias were hidden by the top board and I worked not seeing well.
...Leave a comment:
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Re: Yamaha Tyros strange keys issue
OK STJ I will try and report.
In the meantime I checked all the 61 line's resistence from the 5V to each key's diodes and they results correctly all 33 Kohm as in the schematics
So, increasingly strange...
Regards.Leave a comment:
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Re: HP elitebook 820 g3 (6050a2725001-mb-a01)
Sorry to reply in that thread, someone found the 820 G3 schematic?
Thanks.Leave a comment:
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Yamaha Tyros strange keys issue
Hi, I'm a technician as hobby, I repaired several yamaha keyboards in the keyboard unit (some key doesn't sound or sound too much, etc.).
I'm in trouble with a never seen case regarding a Yamaha tyros 2 61 keys. The problem is that all the couple the D# - A keys sound only the first time I press them. The second time I press them they don't sound anymore. The first time, they sound with a sustain too. The D# and A are on the same wires in the matrix scan as you can see from the attached schematics. I found a video in which the problem is as similar as in my case.
[url]https://www.youtube.com/watch?v=EKascHbPazA&t=707s[/url]...Last edited by daigs; 02-02-2023, 03:11 PM. -
Re: New Members - please post your introductions here
Hello Guys,
my name is Dario from Italy. This forum is a great initiative!
I'm a graduate in computer science with the hobby of repairing electronic stuff, but never touched a laptop's motherboard and thanks to you I would start to do, with your valuable help.
Actually I'm working as project manager in the IT area.
But my mantra is always "Fix don't throw away".
Thank you in advance for all the help should I receive on badcaps forum.
Have...Leave a comment:
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