Cap replacement in M460 modules

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Rich Ardson

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Dec 20, 2019, 10:32:11 AM12/20/19
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Hiya,

I have a 2 x M460D's and 2x M460M's and they all behave differently and need a bit of servicing...varying levels of noise/hum/ eq differences. 

I want to re-cap them - is there any recommendations on major caps to replace, any known typical offenders - or simply ALL of them?

Would be great for any advice

Best,

Lee


Anthony Kuzub

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Dec 20, 2019, 2:17:32 PM12/20/19
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how differently...

Cleaning switches and reseating cards helps a lot.   confirming voltage regulators are behaving is good.

The electrolytic caps need to be changed.   6 at the bottom.   Axial or radial doesn't matter what you stick in there.   I recommend the Panasonic FC series.

The tants will work as they did new from factory until they don't.   They fault as a short a lot of the time... so the damage they cause is more fun.  

Anthony 

 


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warren beck

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Dec 20, 2019, 6:05:36 PM12/20/19
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Hi Lee.

he tent's as Anthony states fail as a short, thus the module will not pass audio.  they have a 40 or so year life in my experience.  As for the electrolytics, axial's are becoming obsolete with the manufacturers.  So radial it will have to be..

Yes cleaning the switches is a MUST!!!!  WD40, or better yet LPS1 - nothing else.

The opamps are not indestructible, but if they go, something else is sick, so explore voltage to the daughter boards first - pull ht boards, and check that 18 - 22 goes there.  Clean the switches as well (I have had switches kill a module, remove all LF from the signal, and other oddities).

Good luck, and enjoy!!

Regards,

Wb!

From: wb...@googlegroups.com <wb...@googlegroups.com> on behalf of Anthony Kuzub <44...@apkaudio.com>
Sent: December 20, 2019 7:16 PM
To: Rich Ardson <fran...@googlemail.com>
Cc: WBSps - Ward-Beck Systems Preservation Society <WB...@googlegroups.com>
Subject: Re: Cap replacement in M460 modules
 

Rich Ardson

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Jan 9, 2020, 2:41:08 PM1/9/20
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Hi Guys,

Thank you so much for responding - I don't seem to receive notifications of this forum so only realised today when I decided to have a look.

So, yes I have varying hiss/hum issues acrfoss the units I have but just general variances rather than anything that makes them unusable, HOWEVER.

One of them before xmas had a number of issues, the HF gain pot was not working, no line in (I rarely use them for line in, but could also be a wiring issue my end for that) and also when I switched on the EQ it would punch in more bass despite the controls being at 0 position.
I did clean up the switches but noticed when I bought this they switches were extremely sticky/stuck in some cases.

Question: What do you refer to as Tent or Tant in your replies? Potentiometers? Sorry, please can you clarify

Since I opened this module to investigate I did infact re-sit the daughterboards etc and re-powered and it's pretty dead, except that i makes an awful crackling sound if I hit the phase switch. When I took out the EQ board it functioned again fine.

So, I've ordered some caps to replace the electrolytics anyway but what could be the problem? I'm gonna clean all the switches and pots again but perhaps I am looking at having to replace one or two of those - 

Lee




On Friday, December 20, 2019 at 7:17:32 PM UTC, Anthony Kuzub wrote:
how differently...

Cleaning switches and reseating cards helps a lot.   confirming voltage regulators are behaving is good.

The electrolytic caps need to be changed.   6 at the bottom.   Axial or radial doesn't matter what you stick in there.   I recommend the Panasonic FC series.

The tants will work as they did new from factory until they don't.   They fault as a short a lot of the time... so the damage they cause is more fun.  

Anthony 

 


On Fri, Dec 20, 2019 at 10:32 AM 'Rich Ardson' via WBSps - Ward-Beck Systems Preservation Society <WB...@googlegroups.com> wrote:
Hiya,

I have a 2 x M460D's and 2x M460M's and they all behave differently and need a bit of servicing...varying levels of noise/hum/ eq differences. 

I want to re-cap them - is there any recommendations on major caps to replace, any known typical offenders - or simply ALL of them?

Would be great for any advice

Best,

Lee


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Rich Ardson

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Jan 9, 2020, 3:09:31 PM1/9/20
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I've just noticed the Voltage Regulators are getting really hot too, sounds a bit silly but the way I have racked these means I cant have the casing open to check voltages, I think I'll replace them anyway

Rich Ardson

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Jan 9, 2020, 3:25:30 PM1/9/20
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And more info - the blue wire attached to the LF pot at the terminal nearest to the casing had come away so I re-soldered that. I have the same problems still, dead unit although it sounds like there's hiss from the booster amp and massive crackling when the phase button is pressed. I think a problem with the EQ side of things has put some un-necessary pressure elsewhere in the unit?

Lee

Rich Ardson

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Jan 9, 2020, 4:34:08 PM1/9/20
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and still everytime I put it back in without the 4-126 EQ board it works fine

warren beck

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Jan 10, 2020, 11:35:34 AM1/10/20
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best to put a current meter in series with the supply voltage.  This will tell you if the positive or negative rails are pulling too much current, thus a sick component on that voltage side pulling too much current.

This tells you where the issue lies.  Next you bring up the voltage to 50% or a little less - the unit will still operate, but not cook.  you can then poke around to find the sick component, and replace it - thus relieving much of the heat for the Tim 29/30 transistors.

Hope this helps

Wb!

From: 'Rich Ardson' via WBSps - Ward-Beck Systems Preservation Society <WB...@googlegroups.com>
Sent: January 9, 2020 8:09 PM
To: WBSps - Ward-Beck Systems Preservation Society <WB...@googlegroups.com>

Subject: Re: Cap replacement in M460 modules
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Charles Beauregard

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Jan 12, 2020, 8:45:15 PM1/12/20
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Hi Rich,

Please take a measurement with a ohmmeter on the tantalum capacitors circled in red on the attached picture.

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4-126.jpg

Rich Ardson

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Jan 13, 2020, 9:24:32 AM1/13/20
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Hiya,
Across those two caps, the top one (pictured) has nothing across it (no continuity, 1 on the meter)
The bottom has 00.7 ohm. But continuity through it.
This is with the board unpowered / removed - just I have it in place and powered on?
Lee
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warren beck

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Jan 13, 2020, 9:28:45 AM1/13/20
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Hello.

I do not see a photo, however Tantalum capacitors - when they fail they short.  This can be the issue for high current draw.  What a friend and I have learned that over 40+ years these Tantalum capacitors start to fail.  Yes tot replace all of them.

Regards,

Warren

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Sent: January 13, 2020 2:24 PM
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warren beck

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Jan 13, 2020, 9:29:40 AM1/13/20
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Ah here i see the photo of the 109 card. Yes go ahead and replace all of the tantalum capacitors.  Will improve the resolution of the LF as well!!!

Regards,

Warren

From: Charles Beauregard <charle...@gmail.com>
Sent: January 13, 2020 1:44 AM
To: warren beck <warre...@hotmail.com>
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Rich Ardson

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Jan 13, 2020, 9:30:18 AM1/13/20
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Thanks Warren,

I'm getting +36V on the positive rail at the 29B voltage regulator and -8v on the 30B regulator, somethings definitely up!!
I've got some new electrolytic caps to replace the 22uf's near the voltage regulators, got new voltage regulators coming too. Some of the resistors down there didn't seem to measure anything, yet the module powers up
Lee

warren beck

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Jan 13, 2020, 9:30:19 AM1/13/20
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ummm sorry in my haste not a 109 card but an EQ card from the 460 series of modules!

Wb!

From: warren beck <warre...@hotmail.com>
Sent: January 13, 2020 2:29 PM
To: Charles Beauregard <charle...@gmail.com>

Charles Beauregard

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Jan 13, 2020, 10:08:02 AM1/13/20
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You can't get 36v there, Are you sure the black probe is t 0V ? 
I would start by replacing the shorted cap you found (the one with continuity) and see if the module works fine. 
The coupling caps rarely go bad. Most of the problem with the M460's are the decoupling tantalum capacitor on the 109 card or on the eq card.

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Anthony Kuzub

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Jan 13, 2020, 12:58:46 PM1/13/20
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agree... there is something wrong with how they are power. 

Backing this up... how are you powering them?

Anthony



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Rich Ardson

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Jan 13, 2020, 1:44:53 PM1/13/20
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Hiya,

Ok, so I'm powering them from a Five Fish psu, Its definitely spitting out +25v, -25v when it is not loaded with the 2 modules I've got connected to it.

A bit of further investigation....
I take out all the boards 2x109's, 1x110 and 1x4-126 and I get +22.2v and -22v on the little + and - positions at the end of the voltage regulation section under just next to the bottom 109 board with my meter grounded at X20 25v com on the pinout

Before I was reading with my meter on the Z22 chassis ground - any reason why my readings would have been so wild measuring that way?

Ok so...
With all boards in I get in I get +19.7V and -20V
With only the 4-110 board in I get +22V and -22V
With only the top 8-109 board in I get +21.5V and -21.5V
With only the bottom 8-109 board in I get +21.2V and -21.8V
With only the 4-126 eq board in I get +20.6 -21.8V

I've ordered some 1uf 35V tantalum caps for the EQ boards, but shall I just replace all of those on each daughter board?

Lee

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Rich Ardson

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Jan 13, 2020, 1:53:22 PM1/13/20
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p.s. thanks everybody for all your help and patience.. I am great with a soldering iron but you are dealing with an electronics novice. I'm desperate to understand this and get it working again, I've racked 4 of these modules into nice wooden cases and I love how they sound. And to my knowledge there's not a lot of us in the UK using these.

Greatly appreciated!

Rich Ardson

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Jan 13, 2020, 2:39:25 PM1/13/20
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And here's my current readings:
Voltage regulators 29 and 30B both 0.2A from them to the + and - next to the 8-109 board
Next:
+ rail to any of the daughter boards are 0.06A and - rail to same board is 0.08A

Anthony Kuzub

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Jan 13, 2020, 2:47:19 PM1/13/20
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Charles is on the right path.   The DC blocking caps...   there may also be something wrong with the op-amp upstream of that as well.

if you're curious about a factory test procedure... https://drive.google.com/drive/folders/0B0yR0b5T78SKMEVDdVk3TzR0Qms  

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Rich Ardson

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Jan 13, 2020, 2:59:59 PM1/13/20
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Cool thanks for this - will read over.

I just powered it all back up again, voltages read ok, just about. Swicthed on teh EQ and got loads of noise then after about 10seconds went back to how it did before, crackling, no output. Voltages on rails went back down to 19V/20V area

I'll start with changing those C49/C50 caps on the EQ board, then start picking everything else apart if there's no joy. When I remove the EQ board, the module is back to normal so gotta be that full stop.

Watch this space ( I hope!!)

Thanks all

Lee 

CHARLES BEAUREGARD

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Jan 14, 2020, 12:13:45 AM1/14/20
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8-109.jpg

And here are the caps that sometimes come bad on the 109 card

Rich Ardson

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Jan 16, 2020, 3:20:07 PM1/16/20
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Thanks very much Charles - I have replaced the 1uf's on the EQ board and waiting for these for the 109's

This problem is never ending it seems - I powered it back up to check voltages are working fine before I re-install the cards and I am reading a positive +22V on the negative rail now, so frustratintg. Its reading negative out of the TIP30B and through to the Q2 transistor but seems to change into positive at the Q6 transistor. I am looking into replacing that pn3645 and the 1n4003 diode - do you think that is the problem perhaps?

Lee

Charles Beauregard

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Jan 16, 2020, 5:08:39 PM1/16/20
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Your probe are probably inverted. Start with all the card remove and add one at a time. You should find on the card about +/-21v on the point circled in red when your black probe is on the tp circled in black on the attached picture.

M460_pwr.jpg

Anthony Kuzub

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Jan 16, 2020, 8:54:29 PM1/16/20
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better yet... proper wiring to the PSU should be inclusive of chassis ground.
Measure relative to the metal chassis.

Look for DC at the signal input of the opamps relative to the chassis.   that is a fun indicator of a bad opamp.   The two tants Charles spoke of, see what they filter from and between... 



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Rich Ardson

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Jan 21, 2020, 1:52:00 PM1/21/20
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An update:

I'm up and running!
At some point digging around I blew a transistor on the minus rail I think when I was checking for current. After getting that up and running and replacing a few diodes I also realised the sound reinforcement board was also causing things to drop so replaced the caps on there, then I realised I had also put a few of the tantalum caps on the 109 and eq boards wrong way round. Then it was apparent a few opamps were dodgy/noisy not functioning well so replaced them. Ultimately the unit has had a nice bit of TLC and i've learnt a lot about the inner workings so massive thanks to everyone for your help, it is much appreciated.

Best regards
Lee 
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