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
greetings all,
a new arrival, a BG8000, which had a partial re-cap job done by the previous owner.
I noticed C24 was put in the wrong way as its positive should connect to the F1 ?!
anyhow, I corrected that, completed the re-cap job incl C27 - see pictures - and now F1 is constantly blowing
even with my DBT ?
I checked D16 to D19, all measured ok.
did I overlook something ? any ideas or suggestions are most appreciated :-))
cheers
ALF
this shows the polarity marking of C24 on the board quite clearly !
Hi ALF,
I presume it is the fuse on the main board and not the one inside the transformer that you are talking about?
Can you confirm that you are using an 800ma 250V quick blow fuse?
Does the fuse blow as soon as you switch the deck on or is it at a later stage of operation?
With the fuse blow have you checked to confirm that the +/- 15 v power supplies are ok?
With the fuse blown are you getting a reasonable voltage at C24 and the ripple looks ok?
Have you checked the D20 zener to confirm it is not shorted?
I'd then isolate 0IC1 to confirm it is operating properly at 5 volts.
Regards
Lonnie
Hi Alf,
You can't always go by the board markings. Your C24 is installed opposite of what it should be. Here is a picture of Beolover's Beogram 8000 and my Beogram 8000 project from a while back. You can see that C24 has the negative lead on the side facing the large C27 capacitor.John
The board has holes for mounting both ways!Often confused.It looks fine.
Martin
Update - I see your problem Alf. I believe you have C24 in the wrong solder holes. Here is a picture of the main board trace side from a recent Beogram 8002 I restored. C24 isn't where the board markings are. It is as shown in the picture. The C24 positive lead does go to the fuse as you expect but the negative lead connects to the negative lead (and ground) of C27.
Dillen: The board has holes for mounting both ways!Often confused.It looks fine. Martin
Yep, I see that now too.
John
There's a negative pad on each side of the positive.Note the jumper!
Yes. If the capacitor had been in backwards it probably would have let him know .
hi lonnie,
I used a 1A /250V fast fuse instead of a 800mA one - no other was at hand at the time, the correct ones are now on order !!!
what happened was : the display went dark, nothing was moving......the only reason for that seemed a blown fuse, which was the case !
yes, F1 on the main board.
I get about 14.3V at C24+ and 23.6V at C27+
D20 is fine.
but: fuse still blows, nothing is moving, no motor no display !????????
Hi john,
good to hear from you again 😁🤗
I actually purchased that table for its transformer, noticed the partial recap job but it was not working.
under close inspection I took the time to finish the recap job as the table is in quite nice condition.....nothing broken, nothing missing.
all connector joints have been re-soldered to exclude cracked joints....
sadly it did not work out - after carefully re-checking for correct polarity of all caps the display went dead and nothing was moving - plus a blown fuse,
which explained.......
i could measure some voltages but do not understand the absence of the 5V and 15V ?
perhaps I should just be happy about having secured a good transformer ?!!
Which F1 fuse blows? The one in the transformer box or the one on the main board? They are both designated "F1" .
Nevermind...I just read and found the answer two posts up.
OK, you have voltage at C27 but in the above post you have indicated an absence of 5 & 15V.
Can you measure the voltage at C28? It should be +15V.
Can you measure the voltage at the anode of D26? It should be -15V.
Can you isolate 0IC1 by lifting R75, adding a new fuse back in and removing connector P6. Measure the voltage at P6/1, it should be 5V. The D20 zener and the F1 fuse are designed to stop anything higher than 6.2V getting to the microcomputer. The fact that the fuse is blowing could indicate a short or too high a voltage?
hello Lonnie,
I can measure about -12.6V at C28, -26.6V at D26 anode
P6/1 shows -5.7V.......
all voltages are negative, which is very odd ???
I think you need to explore your measurements. Repeat the measurements you took yesterday which gave +ve voltages are they still +14.3 & +23.6V?
Use a different ground position?
BTW did the fuse blow or not?
If it didn't I'd add back in R75 but leave P6 disconnected and see if it blows the fuse.
Has the transformer been connected one pin off to the side? Difficult to see in the photo.
And get that dreadful foam away from electronics - and CMOS in particular.You are doing more damage than repairs. Get an antistatic mat.
Hi Lonnie,
yes, I used a different ground position which exactly bugs me, as it delivers different readings !
that is why I atteached a picture to show which ground position I chose today - perhaps you would suggest a better choice ?
the fuse did not blow, so I re-installed R75, the fuse still ok but then p6/1 shows about 12V ! Which is not what we want to see.
with different ground patches on the main board I can find -14.7V at D26 but it confuses me - which ground I should measure against ??
there is something else I found odd because it does not look how the original transformer box was put back in its space ?
you can see the typical green/white earth-wire coming out of the box and gets connected to the chassis - odd because that is not the case
in my other BG8000 plus space for the box is very tight and this wire has almost nowhere to go - will upload a picture shortly.
Quite right Martin,
something I should have done a long time ago - the mat is now on top of my to do list !
no, the transformer is correctly connected but as I pointed in my previous post , I find that green earth wire hanging out of
the transformer box rather odd - it surely can't be original ?? Space to re-insert that box is so tight !
The green wire is grounded to the back right hand corner of the bottom chassis. There is a stud attached to the chassis and a nut screws the green earth wire on this stud.
exactly, that is how i found it but I am pretty sure my other BG8000 does not have that set-up - perhaps something missing
or is it different from country to country ?
I pass on the pics as it seems correct but still feels odd as the space is so tight !
coming back to the original issue :
can you point out a more "suitable" ground patch so measurements can be compared ?
and with the double voltage at P6/1 (just over 12V) after re-installing R75 is this pointing to 0IC1 as a suspect ?
regards
I'd recommend you cool your jets until you get your anti-static mat. A replacement CPU can be hard to track down.
Yes, I know - guilty as charged !
The mat is now in place....finally.....and the jets getting ready to be warmed up again.
first step is putting the correct fuse in place and watch what happens....
Excellent, you must have a good electronics store near by..
You indicated that you bought the TT for the transformer, is it a 220V 50Hz or a 240V 50Hz model?
I'd use the C27 as the ground point , you could clip the com lead onto the light blue jumper lead.
Can you re-do your measurements?
hi Lonnie,
working on the new mat now....!!
the transformer is for 240V 50Hz
new groundpoint in use delivered the following:
R75 in
C27+ 23.4V
C24+ 13.4V
C28+ -0.6V
D26 anode -14.3V
P6/1 unsteady jumping between 0.8V / 6.4V
R75 out
C27+ 23.3V
C24+ 13.15V
D26 anode -14.5V
P6/1 6.5V steady
is that leading to 0IC1 as a suspect ??
The +15V measurement at C28 should be independent of the 5V power supply so I think you need to work out why you are only getting -0.6V.
A couple of basic things to check:
Make sure you measure the positive end of the cap.
Make sure connector P2 is properly inserted. Confirm that there is no shorts between the pins of P2 since this has been re-flowed.
Confirm you have ~zero resistance between the following: the poitive end of C27 and the emiter of 0TR1, the junction between R77 and R78 and the base of 0TR1, the collector of 0TR1 and the positive end of C28.
the resistance between
C27+ and E of 0TR1 is about 0.5 Ohm
junction R77/78 and B of 0TR1 is about 0.5 Ohm
C28+ and C of 0TR1 is about 0.4 Ohm
P2 is definitely connected properly, there are NO ! shorts between its pins.
are these measurements of concern to you ?
BTW it wasn't 0IC1 but 0TR1, the TIP-32 chip as a suspect ?!
putting everything back together with the proper fuse delivered exactly what I feared: blown fuse, meaning the processor protection works
I'd rather see around 5V at 1P6/1
It's not surprising that the fuse still blows, you have made any changes to address the issue.
You have two issues that need to be resolved, the missing 15V and the blowing fuse.
Lets stick with the 15V first.
Can you measure the voltage at the emitter of TR18 / R79 and the voltage at the junction of R77 & R78?
no, I hadn't changed anything - that is why it came as no surprise
junction E of TR18/R79 showed close to zero V
junction R77/78 showed about 23.6V steady
I like to understand the role of 0TR1 (voltage switching?) and TR18
I think I may have been leading you up the proverbial garden path, the +15V coming out of 0TR1 is controlled by the POWER ON/OFF section of the circuit. This is controlled by the CPU and given that you don't have 5V at the CPU to turn the ON/OFF section on you also have no +15V.
0TR1 is a voltage regulator that provides the stable +15V. TR18 helps control the base of 0TR1. Google discrete voltage regulators for plenty of data and descriptions.
Back to the issue with 5V can you test the voltage at c,b & e of TR17 against ground. You will need to put a fuse back in and pull the P6 connector.
oh yes, the garden path......!
finally got to the new measurement:
voltage C27- to TR17, P6 pulled, new fuse
E showed 7.85V,
B showed 7.12V
C showed 7.83V
yes, 0TR1 = TIP32 voltage regulator was the one I suspected to show problems ??
PS: out of interest, where are you located ?
I'd leave 0TR1 for the moment, it won't switch on until you sort the power supply to the CPU.
There should be 5V at the output of 0IC1 and D20 the zener diode should hold it below 6.2V. Given that you measured 7.12V on the base of TR17 and there should be a 0.7V drop across D15 that would mean 6.4V on the output of 0IC1.
There also seems to be too much voltage drop in R75 so I'd pull TR17 and measure it. I'd also check D15.
(Melbourne)
Hello Lonnie,
I did replace TR17 before as precaution - it is a BC557B transistor - and its reading of hfe=310 look ok.
D15 - which funny enough is not even mentioned in the SM ? - shows a OL and 0.560 V readings according to its correct orientation.
So I would cautiously say TR17 and D15 are not faulty - but these 5V must have gone lost somewhere ?
the question, what next ?
Hi all,
I am really not quite clear about what is going on here:
with a new fuse installed, P6-pin1 pulled I can measure the following
TR17. Emitter 6.3V, Base 5.6V, Collector 6.3V
C28+ 14.97 V
D20 5.04 V as well as pin1P6
however, if I reconnect P6/1 the fuse blows........it makes no sense to me unless there is a fault in the processor box or is there not ?
If P6-pin1 shows 5.04 V with the connector pulled the fuse should be fine after reconnecting, unless....??
can somebody shed some light on this, please....
Hi everyone,
here is a quick update of what happened in the meantime:
the fuse issue seems under control with voltage at P6/1 = 5.04V steady.
the +/-15V are not quite there with +/-12.9V at the moment.
the following symptoms are interesting:
all connectors connected -
pressing TURN plattet spins but DBT illuminates, pressing STOP platter stops snd DBT is off.
pressing PLAY platter spins - far to fast ! - and carriage tries to move but returns only after a few cm movement, table does not switch off !
with P4 connector unplugged -
pressing PLAY carriage moves towards the center but does not return, only > or >> can bring it back. DBT stays off.
I feel quite confident there are no soldering bridges nor any cracked joints !
I begin to wonder whether the uP is faulty ?
any words of wisdom from anyone ?
Hello again,
found some time and motivation while waiting for parts to revisit the old BG8000 table with all its problems......
i resoldered the entire main board, so there should not be any source of uncovered issues remaining !
Same test procedure as before:
everything connected
- press 'Turn' and platter spins still too fast plus DBT lights up
- press 'Stop' and table turns off, DBT goes dark
- press 'Play' carriage moves over to 30cm record position, platter spins too fast and arm does not lower, DBT lights up
- press 'Stop' carriage only moves back in small moves each time Stop is pressed. It only goes back to its resting position if '> or >>' is pressed.
I am still barking at the main processor as nothing else seems obviously wrong except the lit-up DBT when the platter starts spinning ??
sadly I do not have a spare processor to cross-check with........
anyone any ideas ... suggestions ?
pleeease
To investigate the speed issue have you read the Beogram 8000 Technical Product Information pdf section 1-9 through 1-11? You can measure the voltage at the gate of 1TR26 to see if pin 2 of the integrator is correctly indicating a positive voltage since your RPM is too high. You can also check if 1D36 is working correctly to keep the positive voltage at no more than 0.7V. You can then work upstream or downstream from there.
The voltage should be measured from pin 7 of the integrator not pin 2.
Check the tacho opto.Check the CMOS 4013 in the tacho feedback.
Greetings,
i
I can reproduce the signal at the collector phototranssitor/1IC1 pin 12 which is Sine-shaped
but at 1IC1 pin14 will not get the straight skirts but a triangular shape !
as for the CMOS4031
red - to pos C28 - shows 4.95V
org - to P6/2 - shows 4.95V
green - to quarz - shows 2.2V
yellow - to P6/2 - shows 3.85V
blue - to neg C28 - shows 12mV
However the voltage at 1TR26/Gate showed -11.5V and Pin7 of the Integrator 1IC3 showed -11.6V
which is not good news ?!!