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
So, a while back I bought a BeoMaster 8000 and it was damaged in shipping. I opened it up to see if it could be repaired, and after setting it aside for a while, I finally pulled the power supply board and noticed that it had been impacted by the transformer, which had come off of its anchorage.
To make a long story short, I identified the traces in the board that had been cracked, sanded them down to expose the bare metal, and soldered them up to complete the circuit properly. I was oh so very proud when I plugged it in and everything functioned as it should have!!!!
I couldn't use it for long, though, as I had not yet attached the three transistors on their own separate cardboard piece to the heat sink, and I did not want to overheat them. So, I reoriented everything, making sure that there was nothing conductive under the board. I screwed the transistors back to the heat sink, without really changing anything else,other than the screws for the heatsink.
I plugged it in and there was no standby light. I pulled the cord, but too late: I had already let the smoke out of something on the PS board. I am fairly certain it was TR6, but cannot say for sure.
Considering that I had maxed out my electronic abilities when I soldered up those traces, I think I must officially give up for now. Unless someone out there wants to walk me through some troubleshooting, or someone has a good PS6 board for me to buy, I'm going to have to keep looking for working units or units for parts.
The rub is that the working units seem to be far away, while the parts units are silly expensive, considering that you don't know what's wrong!
It's a real shame, as it really sounded so good when it was working!
Tom
Noooo Tom, don't give up!
These are not transistors, but regulators. They should be insulated from the dissipator, and you probably forgot the insulators.
Not too bad, these are very cheap! What is TR6?
Could we have a photo of the disaster please?
Jacques
Well, that would make sense, I suppose. The thought had actually crossed my mind, but I figured that couldn't be it. So, there is an insulator between the dissipator (heat-sink) and the regulators? One of the screws also has a plastic washer on it.
Is it all three regulators, or only one or two? It looks like thermal paste should be reapplied, too.
TR6 is on the board directly below the gap between the middle and right-hand capacitors. It is also to the right of the blue and red power cable from the transformer. You can see it in this photo from the Beolover blog:
[img]http://3.bp.blogspot.com/-jHHi8mKYIrA/UAt8l3-5-MI/AAAAAAAAAKg/dHR1-WUfuaQ/s1600/BM8000-3+Board+6+Before.jpg[/url]
I haven't given up, but I am probably out of my league here.
EDIT: Forgot to mention that I have no photos of my own board, as there is no visual damage to show.
Don{t give up, there are help here, if needed you will get step by step help.
Collecting Vintage B&O is not a hobby, its a lifestyle.
OK, I will take heart and break out the multimeter!
Where do I start?
Well you could test that suposedly fried transistor! Unsolder it first, and note down its EBC pinouts, as printed on the PCB. If it's belly-up you might see a tiny crack where the smoke got out!
Test the junctions with your multimeter, diode position: base to collector, base to emitter, NPN positive at base, and PNP negative. These junctions test like diodes: any values from 500 to roughly 700 ohms is okay. Reversing polarities should show infinite resistance.
Also test collector to emitter, there should be infinite resistance too, either way.
See here for further explanations:
http://www.kpsec.freeuk.com/components/tran.htm
Perhaps you mean the 6IC9 darlington?
Jacques,
Well, your instructions read like Chinese to me, but as luck would have it, I am a lucky ***.
I checked the fuses with amultimeter and the 500ma one was dead, and I replaced it. It appears that I am reasonably close to where I was in the beginning, though the unit is far from being without issues.
So, before I go any further, can someone confirm how the regulators are supposed to attach to the heatsink? Here is a photo of what I have:
In fact, I have two of the plastic insulator sheets, but one is still attached to the heatsink. (EDIT: I found the third one!)
As you can see, though, I only have one of the spring washers and one of the plastic washers. Presumably I should have three sheets, three spring washers, and three plastic washers.
Thoughts?
You will need 3 of each, but you need 3 pcs. shouldered plastic (nylon) washers to attach the regulators to the heatsink, you must be absolutely sure that screw and heatsink do NOT touch the metal part of the regulator. And make sure that the regulators are OK before putting them back
The shouldered washer should look more or less like this pic, the one in your pic do not look right to me. The shouldered part must fit into hole in the regulator, and the hole in the washer must fit to the screw.
trymes: Jacques, Well, your instructions read like Chinese to me, but as luck would have it, I am a lucky ***.
Okay, so you will have to read a lot and learn! A new hobby perhaps?
I'm still concerned about that short and the smoke that got out of the darlington though. The fuse let go for a reason...
There is a view (page 5-1 at right) in the service manual which makes clear what goes where by the way.
Well, thanks to you guys for getting my spirits up and providing some perspective.
Chartz: Yes, a new hobby, indeed! I'm hoping to fire up some Open Courseware electronics courses at some point, but I'm still just fumbling along for the time being. I, too, am worried about the darlington, but my current theory on that one is that the solder joints were the cause of the smoke, and the device itself is OK. Besides, after years working on MGs, a little smoke here and there doesn't faze me anymore...
Another thing that the MG link helped with is that I realized that the Philips Head screws aren't really Phillips, they're PoziDriv. Much superior, IMHO, and I luckily have a set of drivers. Phew!
So, I dug around at Radio Shack and found part #276-1373, which came with the proper shouldered washers I needed (I actually found one of the missing two later; no sign of the third one...). That solved my short-circuit problem.
After that, lots of quizzical looks as these various foibles kept me scratching my head:
Anyhow, it's back together and functional, for now. I have no doubt that I will have some more issues with this unit, and I am planning on sourcing caps to replace the originals. After that, the display board is almost certain to start acting up (for now it's still fully functional, believe it or not!). In the meantime, I'm enjoying the BeoGram and BeoCord.
I still need an antenna adapter, but I am pretty psyched. Hopefully she'l stay on the up and up for a while...
Thanks again for all of the help, folks! Now to post another thread to figure out the vagaries of TP2 and if I can use it as an input...
Hi Tom!
Well done indeed! Congratulations!
And what a nice system you have!
All you needed was a bit of comfort, and perpective. You did it yourself! Thumbs aloft then!