hello everyone!

i exchanged all caps on this about one or two years ago and everything was working fine since then. until last week.... the deck started with problems not speeding up to 33.33 rpm, 45 still worked, then it worked fine again for one day, meanwhile it doesn´t move at all, just the coil (the outer one) makes a loud humming and after a while the fuse next to the transformer blows.all voltages coming from the voltage regulations are correct.

first i renewed the transistors 0tr2 and 0tr3 next to the coils and the two diodes there. no improvement, then i checked all solder joints on the edge connectors and resoldered them - no improvement. then i recognized the the transistor ( ithink it´s a BD 438)  on the small outer surplus pcb went hot and renewed it - nothing changed.

what do you think would be the best next step? changing the transistors involved in the steering of the coils or is it more likely, the coils get the wrong signals from the main ic?

thanks for your help!

any ideas are very much appreciated...

greetings from a now sunny and warm munich!

jens

p.s.: when i unplug the leads going to the coils of course the fuse wont blow, as it´s the coils which are drawing to much power... i measured resistance over the coils and it is similar to the coils on my Beogramm 8000 (yes i confess: i´ve got this as well, as i always have to buy it, when i see a nice piece, which is not working and needs some help... that´s kind of a sentimental disfunction [:'(] )

Hi Jens

Contact Martin(dillen) member of beoworld his en expert on beogram's

regards

jan

Does the platter rotate freely by hand or does it bind ?

Martin

hi martin!

the platter isn´t mechanically blocked, it rotates completly freely.

greetings!

jens

Did you replace all the caps in the kit ?

Martin

Hi Jens m

Then I think you must suspect the coils maybe one of them is shortened,which the humming may indicate.

regards

jan

I had a (non B&O) inductive drive turntable, and the insulation on one of the coils disintegrated with age - the symptoms were as you describe.  

hi martin!

yes, i replaced all electrolytic caps, also the one inside the cpu-case, except c19 and c40, as i hadn´t new ones, that fitted there by the hand. it didn´t work when i got it one year ago, but after changing the caps and fitting your tachodisk, it worked perfectly for a year.

hi jan and ray!

i measured resistance over the coils and it´s quite exactly the same as in my beogram 8000, so my guess was, the coil shouldn´t be shorted.

thanks a lot for your input to all!

jens

Hi Jens M

Why do you not try to cut the the connection to the coils one by one and see what happens

regards

jan

latest news:

i replaced the two caps, which were old, but measuring them showed, they were not shorted and still had their full capacity.

o.k., then i put the subplatter back in the gram, what i didn´t do for my last tests and found out, that it´s moving again, the right direction, but not very stable, it reaches more or less 33.33rpm according to the display, the same with 45rpm.

strange thing is, the platter starts spinning as soon as i connect the beogram to the mains. so perhaps i have to check the reset circuit for the ic?

thanks for your help!

i´ll keep you informed...

jens

p.s.: humming is still there.

Hi Jens

It sounds like it isn't coils then, which is good news.  Time to look elsewhere...  

Good luck!

hi ray!

yes, i was quite happy seeing the platter turning again.

changing the transistor for the cpu reset didn´t change anything, perhaps i´ll have a closer look to the brake-circuit,as it feels abit like the platter wants to spinn and brake at the same time or alternating in a certain frequency.

greetings!

jens

jens m:

yes, i was quite happy seeing the platter turning again.

I bet!

jens m:

changing the transistor for the cpu reset didn´t change anything, perhaps i´ll have a closer look to the brake-circuit,as it feels abit like the platter wants to spinn and brake at the same time or alternating in a certain frequency.

That would explain a lot.  I wonder if it is easy to disable the brake circuit to test?

It won't run steady or brake properly WITHOUT the heavy platter.
It is quite normal to see it keep spinning, sometimes even backwards when power is
applied if no platter is mounted.

Since securing a non-rotating platter is part of the processor startup sequence, you can't judge anything
without the platter, it won't get any further in its program before the sensor reports no platter rotation.

They are wonderful machines but not as easy to service as it may seem at first glance.

Martin

hi martin!

i´ll try with the upper platter tomorrow, perhaps i´m lucky and it will run smooth then, but this afternoon the fuse  went off again, so i think, there´s still a problem...

i ran out of fuses and have to get another pack tomorrow.

thanks for your input!

have a nice evening!

jens

I hadn't thought about it, but yes the platter must be on or they go a bit mad.  My non B&O induction turntable used to go into warp speed...  

beam me up, scotty!

latest news:

with the sub- and upper platter the beogram spins as soon it is connected to the mains, when play is pressed the tonearm moves to the startpoint and after a bit longer than usually the platter reaches stable 33.33rpm and then, when the arm proceeds further - looking for some vinyl - stable 45rpm.

when i press stop, the arm goes back and the breakcircuit stops the platter until it stands still, but as soon as the break circuit did its work the platter starts spinning slowly again.

i was wondering, if the bipolar cap inside the housing of the ttransformer could cause the trouble and only could measure, that it´s not shorted and then i had a smaller bipolar by the hand and put it in parallel, just to check, if it´s lacking capacity, but nothing changed. it´s rather hard to get hold of a 39μF bipolar cap...

next thing i´ll do is check the circuit around the coils.....

greetings from bavaria!

jens

Seems to be a floating control signal.
Resolder all plugs and connectors.
Also the row of solders where the ribbon cable from the processor goes to the main board and check that no
leads in this cable has broken.

When you replaced C27, did you remember to introduce the ground connection
as shown in the cap kit inlay sheet ?

Martin

hi martin!

i haven´t had your cap kit, only your tachodisc and took caps from the shop around my corner.

i replaced the 47μF cap inside the metal shielding of the cpu, according to the service manual it´s C28; minus is connected to ground/to the metal case, but i think my connection is pretty much the way it was before, so if you refer to a chnge in how the cap should be connected, i probably havent done it.... i didn´t touch C27 4,7nF though.

i already resoldered the connectors, but i will check one more time to make sure, and will check the ribbon cable coming from the cpu.

thanks alot for your help!

jens

The C27 I am referring to is the largest capacitor on the main board, a huge
aluminum can, 2200uF if my memory serves me right.
It will have to be replaced along with almost all other electrolytic capacitors in the Beogram.
When you replace it, you will notice it has three ground pins of which two are used and must be connected
together again when you mount the new cap, unless you can find a cap of the exact same
type (which is practically impossible).

Martin

hi martin,

sorry, i mistook c27 on the mainboard and c27 on processor board and was mixing up all a bit

yes, i exchanged the 2200μF and connected minus towards c20 minus to close the gap due to the missing connection with the new cap.

i will check solder joints and the ribbon cable tomorrow.

thanks a lot for your help!

jens

i double checked and resoldered all connectors and measured through the ribbon cable between processor and mainboard. everything seems ok here.

then i started renewing transistors and the op-amp in the drive circuit, by the state i´ve reached till now nothing changed in the behavior of the gram:

it starts spinning slowly as soon as it is pluged in and with a vinyl on the platter i realised, the speed is not 100% stable, but something like an oscillating fault like every two seconds.

i think i wil go on with the transistors in the drive circuit...   just can`t find a replacement for the J175...

0tr2, 0tr3 (the ones on the bottom of the gram) and the bd438 on the small pcb still become rather warm when running.

i´m a bit puzzled, if the fault comes from the cpu giving wrong signals or if it is through the drive circuit?????

jens

Please don't replace components in panic, you may introduce new faults.

Is the tachodisc OK ? Is it a steel disc or a photographic ?
Are the sensor pulses from the tachodisc opto OK ?

Martin

hi martin the tachodisc is a new one, steel, i´ve got it from you.

my new observation is, that when the gram is plugged to the mains, it turns backwards for a second, then becomes slower and turns then the right way round...

still the coils are humming and the transistors at next to the coils become quite warm.

how can i see, if the signals from the opto are ok? is this possible without a scope?

thanks for your help + patience!

jens