Help needed with a 22ah585 100Hz problem

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mark3862
Berichten: 4
Lid geworden op: 19 mar 2015, 20:09

19 mar 2015, 20:41

Hi to all from a newbie in Dublin, Ireland. Apologies for posting in English as I have no written or spoken Dutch. I have been restoring a pair of 22AH585 speakers. I have replaced all the Elkos/electrolytic capacitors and the output transistors. When I powered up and started the adjustments of the first speaker I have a continuous 100Hz hum from the tweeter. There is no hum from the woofer. The power supply voltages are all correct. I have replaced the wiring from the transformer to the pcb with a twisted 3 core screened aircraft grade cable as I have access to this cable. In case some of the film type capacitors in the power supply section were faulty I have replaced 2242, 2246 and 2249 but I still have the hum. I am able to set the quiescent current on the tweeter and the woofer amplifier without any problems but I would like to solve this hum problem before I proceed to adjust the amplifier and feedback levels. If anyone has had this problem or has any hint or tips to help me solve it I would be very grateful. Best regards, Mark
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Thomas
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20 mar 2015, 08:58

Hi Mark,

In my experience the 22AH585/586/587 all suffer from some hum. In my case, this is caused by the fluorescent tube lamp that I have at my working desk. These boxes are very sensitive to ambient noise and hum. See if you also have fluorescent lights and turn them off - the hum should be gone. There is a modification to reduce sensitivity for these signals; search the forum for "FTZ" and you'll see that mounting a few capacitors on the preamp board will reduce this problem.
Thomas Baur
webmaster http://www.mfbfreaks.com
De Enige Echte Philips Motional Feedback Website!
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motoindo
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Lid geworden op: 01 jul 2010, 11:04
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20 mar 2015, 09:17

mark3862 schreef:I have a continuous 100Hz hum from the tweeter.
Even if you turndown the tweeter preset on the back ?
mark3862 schreef:I am able to set the quiescent current on the tweeter.
Does that make any audible difference to the 100hz hum ?


And welcome - there no strangers here, just friends who haven't yet met !
yes, been to Johnny Foxes 8)
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Sandrowski
Berichten: 196
Lid geworden op: 24 dec 2014, 21:53
Locatie: Haven van het Gooi

20 mar 2015, 20:50

All depends on how loud they are buzzing. I've just fired up my 585's and they are very softly buzzing through the tweeters. Woofer is dead silent. The buzz on mine is only just above the background hiss so if yours is too then i would consider it normal. If you ask me it has something to do with the tweeter amplifier being placed right next to the bridge rectifier, the charging currents causing the 100Hz buzz. The woofer amplifier is placed farther from the rectifier and is therefore silent.

About the FTZ mod Thomas pointed out, if you look at the service manual for the 22AH587 it's the capacitors marked with a * symbol (only for FTZ). You'll have to solder these capacitors (ceramic ones will suffice) to the bottom side of the PCB, like this:
Afbeelding
Just omit the ones you can't place in the 585 as it has a simpler electronic circuit. The service manual for the 22AH585 can be found here. The service manuals are in Dutch unfortunately, but the schematics are of course language independent.
The FTZ mod won't likely solve the humming issue (it didn't on mine) but it will make the circuit less susceptible to high frequency interference from - for example - cell phones.

In case you haven't done so already, it's worth replacing all electrolytic capacitors in the speakers as they probably have dried out with age. It really improves the sound. Also, a number of components suffer from tin whisker formation, most notably the japanese small signal transistors. Your speakers might have these or they might not. They're usually marked 'C1737' and will most likely have blackened legs. Here is what i mean with tin whiskers:
Afbeelding
See those 'hairs' --> Tin whiskers. They can cause all sorts of strange behaviour as the whiskers are conductive and may short out the transistor intermittently. The Philips transistors - easily identified as they have the printing on top of the casing - don't have this problem.

As you can see from the picture, other components suffer from tin whiskers as well. I've seen them on fuse holders and on the legs of the tweeter amplifier power transistors (6225 and 6226). If any one of these has blackened or has 'hairs', replace them!

Good luck with your speakers! they are very nice and the sound they produce belies their age, humble specifications and physical size. Well worth saving!
Groet,
Sandrowski

What could possibly go wrong...
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Thomas
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21 mar 2015, 20:46

Love your English writing, Sandrowski ;)
Thomas Baur
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De Enige Echte Philips Motional Feedback Website!
mark3862
Berichten: 4
Lid geworden op: 19 mar 2015, 20:09

21 mar 2015, 21:08

Many thanks for all your replies. When I turned down the tweeter level I could reduce the level of the hum considerably. I think I will carry out the FTZ modification and proceed with the alignment and level settings that are on the website. I will report back as soon as I have carried out this work and hopefully will have positive news! Thanks again for all your advice, Mark
mark3862
Berichten: 4
Lid geworden op: 19 mar 2015, 20:09

02 feb 2017, 22:36

Hi to all. After much distraction with work commitments and other projects I eventually got back to the hum problem with my 22AH585. I checked all the transistor voltages in accordance with the tables that are on the pcb solder side schematic and not one voltage was correct! I then considered that I had a basic power supply problem but I had + and - 28 volts at the A45 connector. I double checked this and discovered that the polarity was wrong and I had +28volts on A451 and not -28volts. It appears that someone had tried to repair the speaker before me and had swapped the connections C241 and C242. I remedied this and the voltages came back to normal. I was able to adjust all the values as per the factory settings and my 585s are singing now. Now on to the pair of 586s that need my attention. All the best, Mark
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Thomas
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03 feb 2017, 08:46

Nice you got it fixed! Now that was a problem nobody could have guessed...
Thomas Baur
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Harrie
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09 feb 2017, 23:18

a crazy situation nobody would have guessed .... :roll:
Good that you found the problem and resolved it.
Enjoy your MFB 585 's :wink:
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CD104,CD204,RH831,RH732,RH720,AH794,VR2340,VR600,CD670,CD582,CDR760,CD930,CD100,
DCC951,DCC900,CDi210,VLP720, 2xAH489, 2xJBLG7, 4xAH492H, 2xMFB 587, 4xMFB544, 4xMFB541
mark3862
Berichten: 4
Lid geworden op: 19 mar 2015, 20:09

01 mar 2017, 15:58

Hello all. I thought I would share a little modification I have carried out on my 22AH585 speakers. As my background is in Aviation Electronics it is most important that all wires on an aircraft carrying AC signals (whether they are power or data) are shielded for the purpose of minimizing electromagnetic interference. I used some Raychem 44 twisted shielded cable between the mains transformer and the connections C251 to C253 on the amplifier board. The shield was terminated at and attached to the transformer mounting bracket. Subjectively, this wiring helps to bring the audible level of mains hum right down. I wonder has anybody else tried a modification like this?
Bare cable
Bare cable
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Transformer end
Transformer end
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PCB end
PCB end
mfb3.jpg (53.07 KiB) 5737 keer bekeken
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motoindo
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01 mar 2017, 16:12

mark3862 schreef:I wonder has anybody else tried a modification like this?
That's a really nice solution to a very common problem with the AC wires coming from the transformer secondary. The factory solution at the time was to wrap these in insulation foam which by now has turned into crumble most of the time.

Prefab CAT5 UTP cable 8) could be interesting for our webshop as a 58x overhaul part ...
Albert900
Berichten: 2045
Lid geworden op: 04 apr 2013, 22:56

01 mar 2017, 16:26

Ehhh Chris, the U in UTP is for unshielded, and this modification uses shielded cable....
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motoindo
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01 mar 2017, 19:39

Ah, dacht dat CAT5 wel afgeschermd was, weer wat geleerd !
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Thomas
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02 mar 2017, 13:13

motoindo schreef:That's a really nice solution to a very common problem with the AC wires coming from the transformer secondary. The factory solution at the time was to wrap these in insulation foam which by now has turned into crumble most of the time.
The factory solution to this was to lead the wires at the outside of the PCB mounting bracket instead of inside across the PCB. But this IS a very nice solution! I would almost consider using balanced microphone calble for this but a little more conductor diameter would be preferred.
motoindo schreef:could be interesting for our webshop as a 58x overhaul part ...
Yes it could! Combined with an upgrade kit for the poor speaker wiring as well...
Thomas Baur
webmaster http://www.mfbfreaks.com
De Enige Echte Philips Motional Feedback Website!
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