Beogram 8002 repair – reset circuit?

[premiumverum]

Hi all,

My BG8002 has died. When plugged in there is no response, no standby dot.

F1 was blown, D20 short circuited and blackened the PCB. I replaced both and got the +5v back on P6-1 .However still no response, no standby dot. Due to the damage to D20 I suspected the reset circuit. P6-3 measures +5V, which I think means the reset is active so the turntable wont start up. I checked TR17 on my HFE meter, it had HFE 0 so I replaced it with a new BC557B. However still no response. The three resistors R74,75,76 measure within spec.

First question before I dig deeper: am I correct that the reset circuit is now active and should have 0V on P6-3?

[spassmaker]

Hi

First, F1 is blown because D20 was shot.

D20 is a protection Z diode wich makes a short circurit to ground when the voltage rises above e.g. 6,3 volt to protect the uPC.

I’m not really sure but for me it looks like the reset IC1 PIN39 should have low level.

I would recheck TR17 and C20 and D15.

Maybe member Dillen has a suggestion about the reset state at IC1.

BTW:

Did you recap the Beogram or did you resolder the solderjoints of all plugs so far?

Lot of trouble comes from these failured caps and dry solderjoints.

Kind regards

Christian

[premiumverum]

Thanks Christian.

The BG was recapped 5-10 years ago and any suspect joints were reflowed then. Could of course be a new crack somewhere, I hope not.

Your explanation helps me understand the problem. I am not schooled in electronics but the B&O hobby is teaching me step by step. The function of the zener has made my comprehension of the circuit more clear.

[premiumverum]

OK, replaced D15 with a new 1N4148. No change!

I measured around in the circuit again and read up on using the BC557B as a switch. The 3 resistors are within spec.

Assuming I understand correctly: as the BC557B is PNP, making the base low (0V) should close the switch activiting the reset pin with 5,08V. However, for some reason there is 5,8V on the base. Yet the switch seems closed because C and E measure the same. Why is there 5,8V on the base, why is the switch closed with a positive voltage on the base? Maybe C20 is the cause but I can’t see how?

 

 

[Dillen]

TR17 C-E short?

Martin

[premiumverum]

Checked C-E for continuitiy with the multimeter – nothing. I desoldered TR17, it gave a HFE reading of 381, seems normal.

 

I’m not sure what to do next. Maybe try another bc557b, maybe I got a dud? I could replace C20, unforunately I have no capacitance tester and no 47 uF cap on hand. I’ll have to go to the shop first anyway.

[Francois Lemahieu]

Hi premiumverum, thanks for sharing your progress on solving your Beogram 8002. I also own a Beogram 8002 which is no longer responding when plugged in. People at the local B&O shop told me it was unlikely that it could be repaired as the spare parts were no longer available. I have been trying to get in touch with not so well established repairers but have failed to find one I could deem reliable at this stage. I was thinking of dismantling it myself, although I have no experience in electronics. Would you recommend doing this? Also did you manage to fix yours? How hard was it to find spareparts and who did you go to? Thanks

[Dillen]

The local B&O shop may not be able to repair it. That’s probably true.
But there are countless others who can.
Parts are usually no problem. Most problems are caused by aging capacitors and bad solder joints. All perfectly fixable.

Where are you?

Martin

[Francois Lemahieu]

Hey Dillen, many thanks for your quick answer! I am French and live in Paris but the turntable sits at my mother’s place in Lille (it belonged to my father who bought it firsthand something like forty years ago). It had been working perfectly well until something went wrong (what, I don’t know) in the chest hosting all the hifi/video equipment in a corner of their living room : the TV set, which was plugged in the same extension as the Beogram also did not work for a while after that. But then it started working again with no repairs being made. However the Beogram did not. So I spoke with the staff of the local B&O shop in Lille, who then got in touch with their repair center based in Aix-en-Provence, who provided the “official” B&O answer. I am not schooled in electronics but I was thinking of giving a shot at dismantling it and checking the power supply first. Is that where the capacitor is sitting? As for the solder joint, I can’t imagine them being damaged or bad as they were never touched, but you know better than I do!

 

 

[premiumverum]

Fun to see this post revived!

My beogram is unfortunately still sitting in the closet unrepaired until I find the spirit to work on it again. It is a very difficult machine.

Watch out dismantling it if you are inexperienced in electronics. The BG8002 is very fragile inside. Easy to burn or break PCB traces. And stuck together with foam tape that is now on its last legs. If you are inexperienced you may make things worse. When working however it is a superb turntable. Well worth paying an experienced (!) repairman to fix it.

Repairs are as Dillen says, usually bad solder joints and old capacitors, maybe moving parts lubrication. Maybe yours just blew a fuse but it will be a matter of time before caps and joints start acting up. Check out beolover.blogspot.com for inspiration.

[Francois Lemahieu]

Hi premiumverum, thanks for chiming in! I am very impressed by the work you have already done on your Beogram and sorry to hear that all your efforts haven’t been rewarded yet. Thanks for sharing anyway and thanks for your advice, I will go easy on the machine and don’t plan to go any further than testing the power supply as it seems to be a logical point of entry. Given my inexperience with electronics, I would gladly have B&O look into it however they haven’t been responsive and I find it quite difficult to identify the right repairman for the job, there seems to be a lot of butchers and wannabes around. Many thanks also for pointing me to the beolover blog which is indeed a treasure trove of information!

[Dillen]

Solder joints crack from microscopic vibrations, typically eminating from the mains transformer and from the general
operation of the deck.

I’m sure it can be repaired.
Any french repairers here?

Martin

[Francois Lemahieu]

Hi Martin, thanks for your explanation about solder joints crack.

I looked at the underside of a Beogram 8002 PCB on the Internet, what a nifty piece of work! I also checked a website about soldering showcasing all kinds of jobs gone awry and I can really see myself messing-up this work of art so I guess this narrows down repair options to just one: finding the right person for the job. However I take it that if solder joints are the problem, it should be quite easy to spot any cracks just by inspecting the flip side of the PCB, right? In the same manner, looking for a defective capacitator shouldn’t be too much of a tall order? Do you need to remove it from the PCB to test it with a multimeter?

I have also looked for French forums on repairing B&O antique products but I couldn’t find any at this stage. Will keep looking but it does not seem as easy as finding the beoworld forum (which I did nearly instantly). Maybe it’s a cultural thing…

I have to say B&O didn’t completely shut the door on fixing the turntable. They told me they no longer offered repair services for old equipment as they can’t guarantee the availability of spare parts (which I find regrettable and unworthy of a brand of such high standards by the way) but could have a look at it. They  also told me that I should not expect to see it back before four to five months! But this seems to be the only risk-free option as they are the only established company I could find at this stage.

While I am at it, I also have a question about packing the cartridge. I still had the original triangular box from my Dad, however I think I saw somewhere that there is some kind of plastic cap that is supposed to come onto the cartridge or did I make that up? I did not have such a cap and I just put the cartridge as it was in the plastic box (see attached picture), did I mess up already?

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