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
Hi Alf,
Check my latest post on the Beolover Blog.
A board problem is not always found by checking components and traces. It is kind of unusual but happens more than people think. In my case I deduced from earlier trouble-shooting steps that the problem had to be with one specific part of the board. All of my testing of board components and traces showed that everything was good. But I still had a failure so there had to be a board problem. I finally just desoldered the components in the path with my desoldering gun and resoldered them carefully. After that the board worked again. The problem was probably some cold solder joint that I couldn't see with my magnifier.
So just because you can't find the fault by measuring doesn't mean the board doesn't have the fault.
Focus on the problem area. In your case the fault circuit tripping. Start collecting measurement points from the board that works (in the paths that relate to the fault circuit triggering) and compare those voltages to the board that fails. Take advantage that both output amplifier assemblies are identical to help you trouble-shoot the problem.
John
Hi John,
yes, point taken.....dry joints and their implications if not visible âšī¸
Its ok to do some measurements on the obviously working board but by reconnecting the one on the left (that was ok to a degree that it
did not trigger the safety switch) the safety switch kicks in there won’t be anything to measure......?
another thought as I remember the issue with using the dim-bulb tester.....
this BM8000 being a US model and I am using a step-down transformer.
is it possible when two output amp boards are connected that there isn’t sufficient current on offer causing the safety switch to be activated.....?
probably just a crazy thought but then I never questioned the DBT usage either causing me problems before.
from the design description the safety switch is speaker-output focused only in case there is unwanted DC ??
I noticed that the left speaker 2 termial is disengaged as one of the connecting pins has broken off - in other words unuseable.
off to work
ALF
First can you recheck something?Unplug the +15V connector on the output amplifier board that is not working correctly.Then try turning the Beomaster on. Does the protection relay still kick in or can you power up?If it powers up then check the no-load current of the other output amplifier (the one you consider as good) to see if the voltage across the emitter resistors is stable (and at around 18mV).
If that test passes plug the +15V back in on the bad output amplifier board and try to adjust down the no-load current trimmer to see if you can reach a setting where the protection relay doesn't trip.
Also...right now when the protection relay trips do you see the Clipping lamp illuminate (even for a moment)?
Hello John,
thanks for your concerns...I believe at last some better news:
I reconncted the heatsink block with the darlingtons but did not yet put it up to its holding position.
turmed on the BM and it stayed on, no safety switch kicked in đ
there are still some issues with the adjustment of the off-set on the board that now lives on the left !
I won’t get down to the required 0V and stays at about 8mV.
The no-load current adjustment is still a bit touchy and seem to drift down to about 16.5mV but seem to plateau at that level.
the board on the right has a fairly steady/stable no-load current adjustment and its off-set is pratically zero.
so, in other words it is the board to the left that troubles me still......
I believe there was no need to unplug its 15V supply unless you had something particular in mind ?!
no clipping bulb came on.
Another step in the right direction I hope:
I revisited the board in question and its two trimmers - the no load current adjuster and the DC offset adjuster.
both adjustments were touchy and one of the suspects were those trimmers, despite been replaced with the recap job.
so I decided to try new ones again and the adjustments were definitely much easier.
i took the next step - a bit nerveous though - and connected a pair of speakers......đ
the BM played apart from the annoying display segments missing. I could tune in stations but will also revisit some basic
tuner adjustments as long I can perform them as a next step.
i believe it could be beneficial to follow the different path ways from one of the uP that controls the various segments on the displays
and check the solder joints !!
not expecting any miracles from that exercise but can perhaps revive some segments presumed dead ?!
So, this is the latest from the work room.
well, still on the way to make this beast perform....
not so easy as all interested parties would know !
on the way the Volume Control Wheel malfunctioned: first guess the sender diode and/or phototransistors died......so, they were replaced!
still no function......another close inspection unearthed a dried out joint where one of the blue wires attaches to the control keyboard board.....great !!
an unpleasant task of dis-assembling to get to the joint...reflown straight away, wire reattached....still no function !
another close inspection at both attached flat-band connectors unearthed most of there wire connections were actually broken from bending - also TP2
would not be available...that wire drama explained it why !!
shortened those two flat-band connectors and re-attached all 16 connections......all was well again, volume wheel functions and TP2 back in business.
the flat-band connectors were a bit of a messy job stripping each or their wires individually...not pretty may I say !!
another impression of the volume wheel with the sender diode/photo transistors carrying assembly, replaced with OPA240A and tow OPA550A components
sorry folks,
the last shot is a bit out of focus...its that damn camera I mentioned earlier - much better pic results with my iPadPro but these files are not accepted for uploading for some strange reason ?!
on my way and a couple of important questions at this stage:
how common is it that the no-load current adjustment shows some drifting...same as the DC off-set adjustment ??
and more importantly, if it is what range of drift is acceptable ??
the BM now produces sound on both channels - FM tuner - but it sounds a bit grainy -very lightly distorted - especially on the left channel
one reason I thought could be a out of alignment tuner, so I tried a CD via TP1....with almost the same audio result.
both heatsink blocks barely get warm though......?
on to some basic tuner adjustments....yes, but the Tuning Voltage adjustment (set to 3.0V as per SM) is nowhere near it...no matter what ?!!
the best I can achieve is around 6.5V
well, I shall try and improve on the picture upload and was hoping someone may have some answers to my questions ??
hope dies last as they say
Small steps forward:
adjusting the tuning voltage......read circuit diagram properly đŗ.....board2, P6-3 tuning voltage rechecked and now adjusted to 3.0V as per SM.
no big deal really !
still searching for answers on the no-load current and DC-offset drift and possible reasons.....
Ok,
while I am still waiting for the interconnecting cable signal generator-beomaster areal input for a tuner alignment check I connected a CD player
via TP2......left channel drop outs ...suspected the assigned trimmer, accessable from the left outside of the the BM đŦ
decided to remove the double tuner boards and preamp board, unsoldered the trimmer in question from board #3, deoxited it using deoxit-5
and attented to all in and outgoing plugs the their counter pins on both the preamp and tuner boards.
i could not believe the difference in sound...,no more drop outs via TP2 and even the tuner sounded better - this stuff is magic, highly recommended.
tomorrow will treat the remaining pins/plugs to at least eliminate issues caused by connection issues due to oxidation of pins/plug contacts.
one more interesting observation regarding those missing segments on some of the DPs:
it seems they are not all dead yet and do come on intermittend, begging the question of dry joints and/or driver issues ?
love to read some suggestions from our treasured experts.
thanks
Hi again đ¤
while the interconnecting cable for the tuner alignment is made & deliverd by sounds heavenly (thanks steve !) I deoxited all plugs and pin connectors - can’t do any damage đ no plug has reason to complain anymore of poor contact đ
Next was a revisit to the processor box:
some solder joints looked suspect and will get attention. Next step is to change the old uP sockets to something more upmarket
- gold plated tulip connectors machined ! special care is required when dealing with the chips....antistatic environment a must !
One other observation I mentioned before regarding the missing segments on some displays:
I noticed these segments are not always missing, meaning they aren’t dead yet ?! Unfortunately I do not have the test facilities of Rudy or John
testing the complete DP in one hit.......âšī¸đĸ
i wonder if the two SN74247 drivers becoming unreliable and should perhaps be replaced ?? Comments are invited - as always đ¤
that would certainly be the easier exit rather attacking the displays themselves.....also those logic driver ICs 7/8/9 will be tested....just to be sure.
I’ll be back with more news