Beogram 4000 accident

Hi fellow Beoworlders,

something bad happened to my Beogram 4000 unfortunately. My Christmas project was to restore it. I bought the Beogram some time ago and never got around to fixing it up. I opened the Beogram up and started replacing the electrolytic capacitors on PCB1 as some had started leaking. Replacing the capacitors was no problem: I checked the polarity multiple times after changing them and turned the Beogram on - it worked perfectly. I decided to replace the large reservoir capacitors next, which we’re absolutely shot. Before I plugged the Beogram back in again I checked everything multiple times and confirmed with the pictures I took before taking the old caps out that everything was soldered back in place correctly. I also checked that I had no shorts to ground.

I connected the Beogram to power and turned it on: It worked for about a second until it went dark for half a second and then the lights in the control panel turned on again. I turned power off power as quickly as I saw that the Beogram went dark (my hand always hovers over the power switch on the power strip after replacing components). I inspected PCB1 and the reservoir caps for any visible faults, but found nothing. I then checked PCB2 power supply and that is where I saw something extremely worrying! The zener diode had shorted with the blue wire coming from 0C1. I did not touch this board at all, but I must have nudged the zener ever so slightly. The blue wire is soldered in badly, meaning that it could easily touch the Zener.

Obviously I have not connected the Beogram to power since.

I ordered a replacement zener (I will also replace the other zener while at it), replacements for the resistors close to the exploded zener as they look charred, and I plan on replacing all transistors in the power supply PCB just to be sure (I ordered BC546B as replacements for BC182B and BC141-10 as replacement for BC119). I will also replace the bridge rectifier, 2D5, with B40C1500 (I believe I can replace the B40C800 with the C1500 as the only difference is the higher current rating?).

My question now is: What other things should I replace and check before I plug this Beogram back into power? Your input would be greatly appreciated!

Before I finish this post I want to thank Dillen! The amount he has contributed to the forum and the quality of his posts can NOT be exaggerated.

Enjoy your Christmas and a good start to the new year to everyone!

While I wait for replacement parts I’ve checked various other components of the Beogram and realised that that the trimmers (1VR1-6) are far off from the values noted in the service manual. Can anyone confirm that the values in the service manual are right, as sometimes what is put in the product differs from that is noted in the service manual? Any help would be greatly appreciated. 

Looks like its the 6vdc supply you have lost....it would be a good idea to disconnect the outgoing lead to the rest of the circuit once you have replaced the destroyed parts to make sure you get a good 6vdc supply on power up.....i dont suppose you have a variac so care and luck is required, as for the trimmers I have found some to be different from the manual....if you look closely at them you can often see the value stamped on them, the advice from this site is always to replace components with the same value as those that came out.....unless of course the component is stamped 100ohms and it measures greater or less

Craig

Have a look at the training notes in the manuals section here.......it gives a detailed description of the power supply functionality, its a bit complicated (to me anyway) but its a good read ;¬)

Craig

Craig:

Looks like its the 6vdc supply you have lost....it would be a good idea to disconnect the outgoing lead to the rest of the circuit once you have replaced the destroyed parts to make sure you get a good 6vdc supply on power up.....i dont suppose you have a variac so care and luck is required, as for the trimmers I have found some to be different from the manual....if you look closely at them you can often see the value stamped on them, the advice from this site is always to replace components with the same value as those that came out.....unless of course the component is stamped 100ohms and it measures greater or less

Craig

It is highly likely that I have lost the 6vdc as the zener responsible for the voltage regulation is shot. I will definitely disconnect the outgoing leads as to not damage more of the other circuits. Unfortunately, I do not have a variac to test the Beogram, so I hope that I am lucky. There is a chance the only part causing the problem is the zener diode. I inspected every other board and have found nothing visibly wrong with them. I have to say that the person who assembled my boards did not do a very good job though. The problem with the trimmers is that two of them have a resistance of 0Ohm, so I will probably just replace them with the values noted in the service manual (I can not find any values stamped on them). I do have the service manual which is quite complicated but still extremely helpful (if Ethan is what you are referring to with “training notes”). 

Thank you for your input Craig, enjoy your Christmas and a good start to the new year! I will keep you posted on my progress.  

Today the parts I ordered arrived. I exchanged the 6.8V zener and the charred resistors, even though they actually measured ok. I plugged the Beogram back in and measured good 6.8V and 24V. I decided not to exchange more parts as PCB2 seemed to work normally. I reconnected PCB2 to the Beogram and decided to turn it on. Everything except for the platter motor works perfectly! I am very happy that none of the logic seems to have been destroyed by this accident! However, the platter motor does not spin. It seems like the motor only gets one phase, but I unfortunately do not have an oscilloscope to measure this. The motor only vibrates, if that makes sense? Do you have any guesses as to what may cause this? Any help would be greatly appreciated. I hope everyone on Beoworld had a great Christmas.

I have found the problem, which is slightly embarrassing. Whilst measuring the old variable resistors I changed the value of the motor resistor, meaning that the motor simply did not get enough voltage to run..... Thankfully the Beogram did not sustain any damage from my little accident, I guess I got extremely lucky!