Re: Humming from Mordaunt Short MS502 Speaker Amp
I never did find out what was going on. I'm sure it was a very small grounding issue.
However due to the lack of time and the speakers taking up so much space, I sold them as is with the humming for cheap. I'm sure the buyer will fix them and get them running. They are great speakers.
Thanks everyone for your help
AudioGuy88
Member
Last Activity: 04-14-2024, 07:29 PM
Joined: 06-26-2020
Location: South
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Re: Humming from Mordaunt Short MS502 Speaker Amp
I have taken the humming amp to an old school tech who repairs at a component level. He said he couldn't find anything wrong with it and gave it back to me.
Of course it still humms loudly whereas the other amp is fine.
Unfortunately the tech is 'on holiday' till next year! He's semi retired and only opens when he feels like it. I don't know of another tech who does component level repairs. So I'll have to find this myself.
When the amp is connected to power, it is fine, no humming. As soon as the (-) negative...Last edited by AudioGuy88; 08-02-2023, 10:54 PM.Leave a comment:
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Re: Humming from Mordaunt Short MS502 Speaker Amp
Yes I believe so. There are 2 speaker connections, both have different sized terminals.
The incoming from main speaker terminals/XO only fit 1 way. Have checked that that is correct.
The output to the sub is also correct....Leave a comment:
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Humming from Mordaunt Short MS502 Speaker Amp
I have a pair of Mordaunt Short MS502 speakers.
These have built in amps for the side firing subs.
One of the amps has developed a loud hum.
The hum is quite strange and I can't figure it out.
This is happening to 1 speaker only, the other one has no hum.
The speaker has a Int and Ext switch for choosing the signal. Int uses the speaker inputs and Ext uses RCA.
If you connect just the power, the amp will power on and no hum at all, on either Int or Ext.
On Int input, as soon as you connect the negative (-) of the speaker,... -
Re: How to bias an amplifier
Thanks again for the quick reply.
I take it from the response that variations from 46-52 mV is reasonable and not unexpected. This is good, so I will not worry about it.
I am taking the highest value and setting it to 52.5mV as the manual instructs.
I have connected some speakers to the output without any input and there is a little bit of hiss and static coming from the amp. Not much, but more than you'd expect from a very expensive amp. All the channels do it, and it's certainly not audible unless...Leave a comment:
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Re: How to bias an amplifier
Not sure if I'm doing it right, but I find the values very hard to measure. They will change and sometimes by quite a bit. Also when I remove the mm then put it back the value may be different.
I have used the highest value and have got that as close to 52.5mV as I could.
In any case here are the values I got (mV).[LIST][*]R5 - 50.5 - 51[*]R6 - 51.2 - 52[*]R8 - 46.9[*]R9 - 46.3[*]R15 - 52.3 - 52.6[*]R16 - 49.5[*]R22 - 48.3 - 48.5[*]R24 - 46 - 46.3[/LIST]
I can send you the schematics if you...Leave a comment:
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Re: How to bias an amplifier
Thanks for the quick reply.
I should have been more clear in my question.
The first part is to set the DC servo. It says the operating window is -3V to +3V which I don't understand. However I have set it to as close as 0V as I could.
I have added that to the original post to prevent further confusion.
The manual also tells you to have no speakers connected and to let the amp warm up for 15 mins.
So these measurements are done with no speaker load, powered on for at least 15 mins, and...Leave a comment:
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How to bias a Plinius Odeon 6 channel amplifier
Hi everyone,
I am working on a Plinius Odeon 6 channel amplifier. Not much wrong with it, but I replaced some caps (20 years old) and decided to check the bias current.
The manual says
1.
[CODE]
[1] Check the right DC servo is set within its operating window.
Use VR2 to set TP5 to within –3.0 to +3.0 volts.
[2] Check the bias current is correct once the amplifier has warmed up, typically 15 minutes.
Use VR1 to adjust the rail current to 140mA or 52.5mV across any emitter resistor (35mA per
device).[/CODE]...Last edited by AudioGuy88; 01-28-2023, 10:28 PM. -
Re: How to tell a bad cap?
Thanks everyone for their replies.
I don't have a scope or variac so unable to test it.
But I've got the answer I need. It seems in some cases testing a cap with a tester alone is not enough.
ThanksLeave a comment:
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Re: How to tell a bad cap?
That is correct. I am using the TC1 tester
[url]https://www.ebay.com/itm/263291447651[/url]
There was the brown glue on the bottoms of the big caps. However they were only around the edge and not touching anything pins/pads.
With the small caps I measured:
Small caps
905uF - 925uF 0.2 ohm ESR 1.3% Vloss
Big caps
1400uF 0.18 ohm ESR 0.9% Vloss
Are those numbers enough to indicate if the caps are good or not?Re: How to tell a bad cap?
...Leave a comment:
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How to tell a bad cap?
Hi everyone,
I had a Sunfire True Subwoofer which was making a buzzing noise when it when it was on with no signal. It made more of a buzzing noise when it had a signal.
I figure it was bad caps in the power supply so I replaced all the electrolytic caps. This fixed the problem and there no noise at all, so I'm very happy with the result.
I used both a multimeter and a multi-function tester to check the old capacitors. However all of them measure well within spec.
The caps I replaced were
2 x 1500uf 200v
4 x 1000uf 25v
... -
Re: Info of Relays
Sorry, I forgot to mention that.
This is for a Genesis V amplifier. I believe the same model amplifier was used for multiple Genesis systems.
The Genesis speakers had active servo subs in them, and this was the amplifier which drove them....Leave a comment:
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Info of Relays
Hi everyone,
Hope this is the right forum to ask this.
I have a power supply from a very big audio amplifier which is 20+ years old.
I want to replace the relays in it.
Firstly, should I bother? Are relays reliable and should work for much more than 20 years?
If I should replace it as a precaution, please help me identify what the relays are.
There are 3 relays, 1 x black and 2 x white.
The white ones say 'FKD130P' which from a website tells me it's equivalent to NTE R53-1D30-24. If this is the case, then that's easy enough... -
Re: HP Elitebook 840 G6 Admin PW Help
CH341A I think.
It's the cheap one you get from Aliexpress...Leave a comment:
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Re: HP Elitebook 840 G6 Admin PW Help
I've looked at that and I don't have the skills or equipment to do that.
You can trace the tracks if you zoom in with a camera, but they lead to the smallest SMD I've ever seen, and I am not able to do that kind of work.
I did use a heat gun and removed the chip. I soldered wires to but unable to read or write using the programmer.
So the lesson is the HPs with 1 bios chip is fine and I can do those no problems at all ... the ones with 2 is way beyond my skills.
Thanks again...Leave a comment:
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Re: HP Elitebook 840 G6 Admin PW Help
The 32mb chip is also a WSON-8, but it had pads so I was able to solder wires to it and read/write it without removing it from the board.
The 16mb chip however doesn't have the pads so I will have to remove it. But I don't have the adapters to read it.
So instead of trying to remove the chip and reading/writing. I just want to break the laptop.
I have wiped the 32mb chip, but after a few reboots the machine restores the bios again.
What can I do to damage the laptop so it gets...Leave a comment:
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Re: HP Elitebook 840 G6 Admin PW Help
I think you're right. The chip is IC25LP128 so it looks like the 16mb chip.
However there are no exposed feet/pads, so I can't solder wires onto it. I don't want to remove the chip to read/program it. Very annoying.
But thanks everyone for their help...Leave a comment:
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Re: HP Elitebook 840 G6 Admin PW Help
I am unable to find the 2nd 16MB bios chip. I have taken the board out and looked on the other side but can't see anything which looks like a 16mb bios chip.
I have included a picture of the other side of the motherboard. Can you help with locating the 16mb chip?...Leave a comment:
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Re: HP Elitebook 840 G6 Admin PW Help
Nope. Still asking for admin password...Leave a comment:
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Re: HP Elitebook 840 G6 Admin PW Help
The dump is in the first post.
Here it is again...Last edited by SMDFlea; 04-07-2023, 01:46 PM.Leave a comment:
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