ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Couldn't put of removing the front forever so here goes...…..really is starting to look bedraggled now!
Little wonder there was a lot of crackling going on.....awful lot of dust on the linear potentiometers...….
Will work my way through each one in the coming week
Had to modify the mounting bracket to accommodate the considerably smaller smoothing capacitors.....
Following a good clean I've used silicone grease on the guide shafts and graphite grease on each internal slider, they feel a lot happier now.
The whole thing is starting to look much better....
I'm questioning the need to rip this side down any further just to chase the bits of dust still left, no corrosion like the transformer side....will sleep on it.
took the side panel off anyway as it was only a couple more screws......
And there was some corrosion hiding away under the PCB, the feet also needed some attention....so I feel vindicated.
Good stuff Craig,
Well done so far.
I did mine while ago and still working impeccably. If you need modern equivalence for the transistors on the output stage or anything else, you know how to reach me!
Popcorn time watching yours!
Oh BTW, the capacitor trick across the switch contact and AC line (after the transformer) reduces the pop noise quite a lot!
I'm getting close to starting re-assembly, I'm not keen on going any further with regard to de-soldering all the wiring harnesses simply for the sake of doing so. I will go ahead and re-assemble everything back to a power up position, changing any caps that are easier to access whilst stripped down, and test run again to see if I have eliminated the hit and miss, scratchy and hissing output I was getting on initial testing.....having read Sorens post the general consensus regarding the semiconducters would appear to be leave well alone, I will clean them to remove the traces of oxidisation and if that still play well I'll keep them. Should all be good I will start to replace all the capacitors and think about the front panels.
Replaced these two 4.0uf with two 4.7uf while I hade the front panel removed
The two originals looked quite sorry.....seems they had burst open at one end! measured up at twice the specified value.
Started to replace the end plates and transformer enclosure
Re instated the transformer and wired it up...connected the smoothing caps, did a visual check all around. Gingerly powered back up with the variac….pulling very little current. connected a pair of speakers and an Ipad via PHONO set to HIGH and went again.....was rewarded with a nice rich sound.....but only from the right channel! wouldn't be the same if everything worked first time. however all the nasty crackling and intermittent operation has now gone...volume moves up nicely balance moves the sound from right to nothing and all the selector switches are working fine.. removed the speakers and Ipad...set volume down and measured the quiet current in each output stage....both are sat nicely at around 4.4mV....so its not all bad news ;¬)
Ok....following the best part of half a day injecting signals and following them around the various circuits, using the halfing technique, prescribed by the man himself, I found I had an intermittent fault....signals present during one measurement would disappear frustratingly the next time I looked for it meaning I was going back and forth far more than I should have needed.....they are the best ones I'm sure everyone will agree. However in the end I discovered what was going on, the HIGH-LOW selector switch for the PHONO is not what it should be, jiggling it brought the missing channel back up. will need some more cleaning, or perhaps I will change the wiring around on the AUX input so I can connect through that input instead.....bottom line is that I now have both channels working and sounding very nice ;¬)
Oh....and Martins lamps showed up today too, another tick in the box ;¬)
changed these little devils out today to enable me to replace the bottom covers...again the originals where way off spec, but still working and sounding sweet it has to be said.
Going to make a start of the amplifier and tone board next....sort out the broken corner of the PCB too
Good helping of epoxy may do the job, If im careful when I screw it down, fortunately no tracks have been damaged
Will work my way through all the caps....
Moving on.....completed this board
Nice work - as always.That corner is a known problem:https://archivedforum2.beoworld.org/forums/p/5230/125965.aspx#125965
Martin
Thanks for those words of encouragement ;¬)
I have arranged with Frede to supply a pair of refurbished front panels, felt like the right thing to do to get this piece back to where it should be. Frede hasnt got any aluminium curser trims however so I will have a hard look at those I have and do what I can with them, they are not too bad and I have a set of new lens provided by Martin so im confident all will be well. The corner of the board in question was also cracked on Peters machine, and then repaired I suspect by Frede....clearly is an issue going on there.
Craig
Did you find out why mine was misbehaving? Sorry not been in touch as had a few things come up!
Peter
No worries.....I'm still using it! since cleaning the switches and linear pots, graphite greased the tracks, yours has performed fine. When I'm done with mine I will run a full comparison between the two....see if anything sticks out ;¬)
Did I bring down the manual with the test certificate from Frede? - it gave the values before and after restoration.
Craig,
The two capacitors at the top edge of the tone control board have to be mounted horizontally like the originals otherwise they will interfere with the heatsink.
Regards,
Jean
Very good catch!....I lowered the tone board all the way down and sure enough the 100uf cap was just resting on the cover for the Darlington transistors, changed them both out for good measure....thank you, I appreciate your vigilance ;¬)
Didn't gat an awfull lot done over the weekend due to a day spent at a blacksmiths forge! some may say it reflects my approach to restoring stuff in here !! but was great fun hammering hot metal
However...did some catching up and now almost half way through the output stages.....trimmers too
And the picture I failed to include...
You may want to check the slack on those transistor heatsinks. They get loose and heat transfer is less efficient. Close the gap until they are snug and you'll be fine.
Thanks for that...I will take the time to ensure the heatsinks have good contact with the transistor cans...I have been remoning the oxidisation from the cases of the rest of the transistors.
Pretty much done with the replacement components....just awaiting delivery of a 5k pot for the power supply and I'm done.
Set the quiet current and symmetry adjustments with no drama, lowered the tone board into place and screwed it down, then remembered I hadn't put the cardboard cover on top before putting the screws in...….
lowered the output stage board and was able to flip the whole thing over and take a look ate the in/out sockets that I knew where in need of some attention
they have oxidised nicely with the passage of time.....will get the Dremel involved
came up nicely...…..