Hmmm. TR9 which is connected to TR17 was also busted. On replacing the transistor it immediately blew when power was applied (through a variac). There appears to be a short somewhere, I need to check if TR17 survived this. The power supply before the fuse is fine, all voltages are good if C12 (2200uF) was bad it would have killed the 12v power regulator as well (but it is fine).

So it has to be something downstream. The motor is good, I can apply just 4v DC and it spins without a hitch. I can move the two reel tables (I think that's what they are called) by hand, no issues. There is a small motor on the backside of the tape assembly, this also works fine.

I have checked all of the transistors in the chain leading to the motor in the schematics and can't find anything out of the ordinary. Only near the power supply are 2 blown transistors of which one blows immediately after replacement.

I need to think about what the hell is happening here. Cascade like this is not normal.

Bert

 

TR9 (BD435) is fine. So it seems that the TR17 is where the problem ends. I need to think about this because I just can't find anything wrong. Desoldered all transistors in the pathways to be sure, they all test fine. F32 transistors also all fine. No shorts. So why this transistor blows in such a simple circuit when not even full power is applied is a mystery at the moment.

Suggestions are very much welcome :-)

BB

Desolder/remove TR17.

Use a seperate power supply and send 14V with limited current instead TR17... and check wether there is a short in the system or why it needs so much power.

Dont blow some transistors, use a regulated power supply instead. Try less than 14V and limitied current...

Okay check, no problem. I'll start with injecting about 2v as I would see a current draw far above what is reasonable already. Can always ramp up the voltage a bit at a time.

Thanks!

BB

Okay, I think the problem is mechanical. I've setup the system in such a way that the power is all external. When I press play the left reel spins but the right one does not (see image). This would put undue stress on the lowly BC547 causing it to burn. Likely as a protection for the BD435.

Login to view image

Now my question is: how the hell do I dismantle this deck? Is there anything in the way of a 'tutorial'? It doesn't seem to be all that easy and mucking around in B&O decks is a sure way to never having a working deck again.

Many thanks!

BB

Also, I am wondering what the hell actually happened. The deck was playing fine for some 30 minutes. Then it started to slow down and eventually stopped, causing a cascade blowing the two transistors and burning the resistor. I have this hunch that more is going on here than just a bit of lubrication.

Bert

Hi Bert

You mentioned the small Motor on the back, please check if the plastic gearwheel is tight fit to the motorspindle, had already two which were cracked and slipped through / did not really turn the other gearwheels completly, so the drive got stuck in some unusual state, sometimes worked sometime only fast forward and so on.

If cracked you could glue it back in place with superglue, worked fine both times.

Kind regards

Christian

Remove the black cover... 4 bolts on the backside.

Remove the small plastic c-ring on top of the wheel.

Clean with alcohol isopropanol. The grease can be very sticky...

Hi all,

sorry for the late reply. I have an eye disease and sadly I am sudenly almost blind.

I was able to repair the Beocenter by dismantling the entire cassette mechanism and relubing it all. Now with the replacement transistors it is all working fine again. It is likely to be my final repair :-(

Many thanks for all the help,

Bert

i have a question. and wondered if you'd seen the same. on the underside of the tape deck the belt on the smaller white capstan is constantly in contact with the large aluminium wheel.

Also these seem to be going all the time and never stopping even if playing the radio.

thoughts? Thanks