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 All,
back in the work room to tackle the next road block: record detection 😡
the carriage won’t stop on its way in at the drop-down point (25/30).
the 25/30 = low, the switch is not the problem but the DR signal is low, meaning the pick-ip arm won’t lower.
the filament lamp in the detector arm is ok, however I do not trust the BP-100 element as I do not get any
Meaningful signal into the base of TR14 !!
i can measure the resistance of BP-100 under different light conditions which was somewhere between
200kOhm and 25kOhm ???
with a record on I should see 6V at the TR17-C and TR18-B….but no, not present.
I certainly can not replicate the signal as shown in the SM with the scope…
Does that mean I have to replace the BP-100 element ??
BP100 is not an LDR.It's a voltaic cell.It produces voltage when light shines on it.
Martin
Oh yes Martin,
of course…meaning measuring resistance is totally meaningless.
in the absence of any decent (voltage) signal from that part I should conclude it is indeed faulty !
so, off to find that Osram ‘photo transistor’ LPT 80A…..
ALF
ALF: in the absence of any decent (voltage) signal from that part I should conclude it is indeed faulty !
Yes. But make sure you measure correctly. It only produces a very small voltage.
With no record on I should see a pulsating voltage of around 20mV at the base of a1TR14 !
what I can measure (DMM) is a pretty much stable 620mV voltage at the base - it doesn’t change with or without a record on the platter ?
if the filament lamp/BP100 assembly is taken off the detector arm I can expose the BP100 to changing light conditions and it showed between
25mV and about 150mV on the little connector board ?!?
that would at least indicate the BP100 isn’t dead but isn’t right either !
trouble is I am still not getting a high DR signal, freeing up the pick-up arm lowering ? Why ?? Because the system is not registering the record ?!
it looks very much like replacing the BP-100 unless someone can make a different suggestion leading to the arrest of the culprit.
Good news guys,
Often helps to have a nice civilised cup of tea before rejoining the battle !
it did not make sense to measure something that delivers sensible outcome once its taken off the detector arm
and mounted (in-circuit) delivers nonsense !
I simply followed where and how the BL-100 is delivered to the main board - what did I discover ? A broken wire connection near 1TR14 and its capacitor.
all good for now 😩😕😁👍
I was beginning to scratch my head...
Good Alf! 😃
Jacques
well, one can never scratch too much…..
having said this, i am still trying to chase an intermittent fault where the carriage moves to the drop- down point but doesn’t
lower the tonearm ?!?
now, i have played the same record about 20+ times in succession without any trouble but then out of the blue this damn
fault turns up again 😡
the solenoid switch works fine, I checked the diode EM504 (=6D1) which displayed about 80mV in both directions ??
the record detection obviously works.
the piston dampener isn’t blocked……question is: is it a mechanical or electrical issue ?
ideally it would be both…!
any words of wisdom from one of our many experts ?? of course I could go on to a wild goose chase, but do you measure when
everything works - when it doesn’t it comes as a surprise.
help would just be great……thanks
as I see the issue:my suspects are :
the EM504 diode (6D1) - possible leakage ?
OTR4 = TIP42 with intermittent fault or possible bad contact to one of the wires attached ?
the solanoid switch, requiring contact pin readjustmemt ?
everytime that issue occurs I fine-sanded that switch and operated the solanoid by hand……all worked fine afterwards !
any comments ?
regards
From my experience, intermittent problems are solved through either the “shotgun” approach where you replace all possible suspected components or by removing components from the suspected list by testing the different circuit paths. In your case, you don’t mention whether the arm when not auto-lowering can then be lowered using the down key. Why this is important is that there are two circuit paths. If you cannot replicated the problem by simply cueing and you can also lower the arm once its stops at the start of the record, then you know the common components are likely fine and you should instead focus on the unique components in the auto-lowering path. Can you verify if that is the case?
ALF: i am still trying to chase an intermittent fault where the carriage moves to the drop- down point but doesn’t lower the tonearm ?!?
i am still trying to chase an intermittent fault where the carriage moves to the drop- down point but doesn’t
You say the solenoid switch works fine so does that mean the arm reaches the set down point and you observe the solenoid click/engage?If that is the case are you saying you can see the solenoid rod move the arm lowering lever?Or are you saying the solenoid doesn't engage when the problem occurs? If that is the case do you hear the solenoid attempt to engage or is it not getting a command to engage?
John
Hello Mark,
thank you kindly for your reply and sorry about the delayed response as I was quite busy with my Quad speakers restoration..
back to the Beogram issue:
Randomly the carriage moves to the drop-down point and nothing else happens !
you can not manually lower the arm via the keyboard but you can operate the carriage forward and reverse or simply press OFF to end.
when that scenario happens the solenoid does not engage.
if you however operate the solenoid “by hand” the arm lowers and stays down……the record plays.
having said this,
You start the process again by activating ON everything works as it should ??
it did so dozens of times without a hick-up !
Hi John,
nice to hear from you…..
when the issue occurs the arm moves to the drop-down point but nothing else happens, no solenoid action at all.
as explained to Mark, you can not lower the arm at any point manually via the keyboard,
You can however use your finger to operate the solenoid and the arm would lower and stays down, the record plays.
if you start the process again by activating ON everything could quite easily work again as it should ??
i started that process numerous times in succession without a problem but then out of the blue it plays up again.
There has to be a “weak” component somewhere which obviously gets pushed over its limits occasionally ??!
Hi Alf,
I would monitor the control signal for the solenoid activation and see if it is present when the arm is to be lowered. I would also pull out the solenoid and try to operate it with a DC bench supply to see if it engages and how much current is required to engage it.
Clean the switch contact for the solenoid power. The one that shorts the series resistor until the solenoid has done a full travel.
hi John/Martin
i will keep that in as a next step - at the moment it is working after I cleaned and deoxited the solenoid switch Martin mentioned.
there are some reservations whether this is going to be the long-term solution or the solenoid activation signal isn’t what its supposed to be….
as said, right now it is working (again)
thank you both for your input 👍
regards, ALF
If not perfectly clean and aligned, the contact will be somewhat erratic.
It will work for a while, then not.
Absolutely !
Rest assure, I will monitor that contact switch with both eyes and have done some alignment already.
if I could find the energy I would take all those brass contact switches out and get them gold-plated.