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
I am going to monitor some other signals next. In looking at the result so far, here is some more detail of the problem.In starting from a standby/stopped position, pressing Play causes the most stress on the problem. That results in the brightest flicker on the dim bulb tester and often results in the turntable immediately returning to stop. Occasionally the Play is able to get passed that startup surge and continue on. However, when it reaches the point where it needs to accelerate to 45, I see a dimmer flicker on the tester and the 8002 returns to stop.When I don't press Play first and begin by using the Turn button, I only see an initial, dim flicker on the tester and the turntable does turn. Pressing Play after that doesn't cause any stress on the circuit that results in a dim bulb flicker. Changing speeds to 45 is the next time I can see a surge.
When I begin with the Turn button then 45, then Play, the tonearm will travel its full distance as it should and there is no dim bulb flicker after the speed change to 45.
-sonavor
sonavor: I am going to monitor some other signals next.
I am going to monitor some other signals next.
I moved the scope probes to the positions shown in the diagram. These measurements are at the transformer secondary that are used for the 8002 drive. Probe 1 is on transformer connection P7-5 (b) and is near zero when the 8002 is in standby (stopped with power on). Probe 2 is on transformer connection P7-11 (c) and measures around 30 VAC, 60 Hz in standby mode. When I press Turn or Play, the signal increases at (b) and decreases at (c) then they settle out.
Here are those same signals across a wider time range at start up and stop. I need to rerun the Stop test because I forgot to note whether that includes a speed change up to 45.
Continuing with the oscilloscope monitoring of the transform secondary that connects to the 8002 drive circuit. With the scope probe 1 (Red) connected to (b) in the schematic and scope probe 2 (Yellow) connected to (c), I measure the following for the entire startup sequence for this BG 8002. Since this captures a good startup, it means that the dim bulb tester only barely lit up on the start. The two pictures below make up the full start from standby to a steady turning of the platter at 33 1/3 RPM. I believe this is the correct behaviour for the 8002 here but I still have yet to find the source of the current surge I am seeing. It is also a mystery why sometimes the surge at startup is greater than other times. It does that randomly as far as I can tell.
As another quick test to try I swapped out the tonearm motor and belt from my spare BG8000 unit. I had to use both the belt and motor assembly because the pulley capstan on the 8002 has a larger diameter than the 8000. It turned out to be a deadend though. The problem remains the same.
John, I think you are a little of track here, start and speed change are powering the main motor, the tonearm motor does start and stop but there is no speed change, I think the power surge must come from the main drive circuit or motor.
Collecting Vintage B&O is not a hobby, its a lifestyle.
Søren Mexico: John, I think you are a little of track here, start and speed change are powering the main motor, the tonearm motor does start and stop but there is no speed change, I think the power surge must come from the main drive circuit or motor.
Yes, you are quite right. I was just looking for something to try and since that motor was turning during part of the operation I decided to just check it.
Anyway, I think I have gone over this Beogram 8002 pretty thoroughly now. The power rails are good. The solder joints all look fine...I have resoldered all of PCB1 since I started this. The voltages on the AC power to the motor drive looks like it is working okay. There is just the power surge when the drive accelerates - at the start and when increasing speed. So 0 to 33 and 33 to 45. That makes sense that those would be the times that demand the most load.
I was thinking about flipping the switch on my dim bulb bypass and seeing how the turntable performs. That will be at the risk of blowing another transformer fuse. However, I have spares. My bulb that I currently have in the dim bulb tester is a 60W bulb. The rated power consumption of the Beogram 8002 is 15W. Instead of bypassing the dim bulb part , I decided to change the bulb to a 150W bulb (because that was the next size I had around to try). In that test, the bulb never illuminates and the turntable goes through its motion like it should. Of course that was what I observed back at the start of this project, right after the recap and before my first transformer fuse blew. Maybe the 150W is too big for this situation? Does that mean the 60W bulb is interfering with normal operation of the BG8002 or is it protecting it? I left the 150W bulb in the tester and ran the turntable for about an hour. I didn't experience any problems...other than the nuisance problem of extra segments in the display illuminating. I'll continue and run the turntable for a longer period of time tomorrow and see if the transformer fuse holds up. -sonavor
Undersized transformer perhaps. They always hum slightly I find, on Beocords or Beograms — not earlier 4000 series, they are completely silent.
Bean counters I hear?
John, just put the whole thing back together and send it to me for my birthday!
Jacques
Is it possible to change the main motor with the one from the 8000, or did you take the motor apart for cleaning and lub. And did you try running with an Ampmeter on the motor mains, variations during run will show if the bearings are OK or not. As the failure is "uneven" dry or bad bearings could cause it.
And of course a small transformer will make it even more important that the motor is running without problems, When I start up machines after installations or big repairs, I always check the Amps and voltage on all 3 phases during the first start up and test run, this saved my but a couple of times.
The Beogram 8002 doesn't use a conventional motor with bearings and a shaft. It has a tangential drive system. The base platter as shown in the picture below is actually the rotor in this system. The platter that the record rests on goes on top of the rotor. The transformer looking thing that the rotor passes through is the stator. So the motor in this system doesn't have any moving parts. There are just bearings that the turntable hub rotate on (I've not taken that apart and don't intend to).
In these two pictures I show the rotor in place with the stator (1st picture) and the rotor removed (2nd picture).
chartz: Undersized transformer perhaps. They always hum slightly I find, on Beocords or Beograms — not earlier 4000 series, they are completely silent.
I don't think it is a transformer problem because I tested already using a transformer from another unit. My birthday is coming up and I was hoping to make this turntable my present :).
Søren Mexico: Is it possible to change the main motor with the one from the 8000, or did you take the motor apart for cleaning and lub. And did you try running with an Ampmeter on the motor mains.
Is it possible to change the main motor with the one from the 8000, or did you take the motor apart for cleaning and lub. And did you try running with an Ampmeter on the motor mains.
I do have the option to change out the stator assembly with the 8000 but I think that will be a last resort. My dim bulb/variac test device has a built in ammeter and voltmeter. The ammeter scale goes from 0 - 10 amps so it isn't for making low current measurements. However, I can observe that current to the 8002 is far below 1 amp. When the turntable starts up or the speed changes I can see a very faint wiggle on the needle.
So I am still trying to figure out what affect the dim bulb tester might have had on my testing. Before using the tester I blew out the transformer fuse twice. That was back when I had just done the initial recap of the 8002 and was testing the operation of the turntable. Leaving the 8002 on standby, it began rotating the platter by itself and then lost power (fuse). Since then I have been testing with safety of the dim bulb tester. The bulb I used was a 60W bulb. The 8002 is rated at 15W of power usage. I observed that on startup and speed change the 60W bulb would briefly (1 second) illuminate at different brightness levels. When I switched to a 150W bulb, I no longer see any illumination of the bulb and the turntable operations appear to work. Today I am operating the turntable with the dim bulb bypassed. Operation so far is normal and I am going to leave the 8002 in standby most of the day to observe it.
Sorry didn't do my homework, the rotor has bearings and there you may have the problem, or was it possible to get some lube into it. The power surge is at start up and speed change and not always the same. It will be interesting to see changes in the surge after running the deck some hours.
I am thinking now that the surge I am seeing is normal. My oscilloscope measurements didn't show any shorts to ground. I didn't post any pictures but I also monitored the 15 VDC rails during the speed changes and they remained steady. Today I found a 100W bulb so I removed the 150W from the dim bulb tester and put in the 100W. It also doesn't show anything during the surges and the ammeter barely wiggles. Next, I swapped the 100W bulb with a brand new 60W. The 60W draws current and the turntable problem returns. So even though 60W is four times greater than the BG8002 rated 15W, it appears to be affecting the testing of the turntable. One thing I can try is to take my working BG8002 and use the dim bulb tester (with a 60W bulb) and see if I get the same result.
Will be interesting, I have problems getting bulbs higher than 60 W down here.
I verified that the 60W bulb in the tester is causing the problem. My working BG8002 tests the same as the BG8002 in this thread when running it through my dim bulb tester (with a 60W bulb). So my trouble-shooting exercises for the past week turned out to be an exercise in learning more about the BG8002 drive circuit....still useful :). A reminder that I am still an infant in this hobby. But the learning experience is the enjoyment in it for me. I feel quite good now that I might be close to having a second working 8002.
What remains now is to fix the display problem with the extra segments illuminating. I also have to repair the double-sided tape of the tonearm cover and the deck of the turntable. I am not satisfied with the repair on the turntable cover either. I fixed the spring loaded mechanism where it works but compared to my other BG8002 and the BG8000 parts unit, it doesn't look right. I might just swap covers with the BG8000.
sonavor:But the learning experience is the enjoyment in it for me.
For us too John, it has been good lessons, give the cover one more try before swapping.
I can see the problem with the cover hinge now. There is supposed to be some double-sided tape that holds the hinge assembly to the lid deck. The BG8002 in this thread is missing that. This picture shows the BG8000 with the hinge assembly properly configured. You can see that the BG8002 is not properly secured. I still want to take the cover from the BG8000 though because the plastic cover that hides the actual hinge from being visible (when using the turntable) is broken off the BG8002. It came that way and even if I glue back in place, it will still look marred.
Jon
This is a linear supply, as opposed to a switching type.
A DB Tester WILL inhibit correct operation of a DUT which contains a switching power supply.
On this linear supply, no matter what size bulb you put in the Dim-bulb tester, operation will be the same (when the DUT is technically OK), whether you see the bulb illuminate or not.
In other words, if the BG8002 is OK, the DB tester will not interfere with correct operation.
So, there is no gain in using a 150W bulb to fool yourself that because the bulb doesn't light up, that the 60W is causing the problem.
If you've ever troubleshot a BG4000, 4002 or 6000 (AC motor) the power variations are beautifully illuminated on the DB Tester.
Continue using the 60W bulb, or even a 40W bulb, until the problem is solved.
In my test though, the 60W bulb is also causing my good BG 8002 to fail the same way. What I was saying is that I have my everyday Beogram 8002 turntable that works perfectly...and when I connect it up to my dim bulb tester with a 60W bulb, it illuminates the bulb on start up and speed change just the same as the BG 8002 in this thread.
I think I now have all of the known electrical problems fixed on this Beogram 8002. I say known because I have yet to have this turntable where I can attempt playing records.
Tonight I replaced the PCB2 IC2 (7-segment display driver). That didn't fix the problem with extra sections of the segments lighting up intermittently. The next step then, was to put back the original IC2. I made that step a little easier having installed a 16 pin IC socket on PCB2 for IC2. One note about that - on the original IC2 attachment to PCB2 (without a socket), IC2 pin 8 (ground) was soldered on the component side of the board. The trace side does not have a pad for it. So when I installed the socket I added a jumper from the trace side pin 8 to ground. That was because it was too difficult for me to do it on the component side. Since the 7-segment display driver didn't fix the problem I reasoned that the problem could be with the display itself or with the transistors IC3, IC4, IC5, IC6 and TR1. I removed the transistors from the board and tested them. They all measured good so I resoldered them back in place. For the display, I swapped the display and cables with the Beogram 8000 parts unit. I felt it was easier to just solder the cables to PCB2 rather than to the small display board.
With all of that work done, the Beogram 8002 display now works properly again. I have left the unit on for over an hour and haven't seen any problems with the display. I plan on leaving it on overnight. If all is good in the morning I will start working on putting the Beogram back together.
Congratulations John, I really cross my fingers, that everything goes well tomorrow, hurry slowly and dont forget anything
The Beogram 8002 is still working properly this morning. I left it in standby mode all night. The display works fine and I ran through a few commands (Play, Turn, Stop).
Now to work on re-assembly and fixing the mechanical pieces.
Champagne!
Here's to you!
chartz: Champagne! Here's to you!
Thanks! I appreciate that.Before I start putting the turntable back together I checked playing an LP. I wanted to make sure no adjustment was needed in the tonearm set down posistion. For this test I used an old LP (Wheels of Fire by Cream) that is a rather beat up copy...not my playable copy. I also used an old MMC2 cartridge that I keep around. It has a channel going out and I plan to send it to some place like Sound Smith but I haven't budgeted for that yet. The Beogram 8002 had no problem detecting the record and setting down. I also tested the Pause functionality. Choosing a spot half way into the LP, I pressed Pause a couple of times so the Beogram returned to rest. When I pressed the Play button, it returned to the location I had paused and began playing again.
The Beogram 8002 display is now bright and clear without any extra segments lit up.
And from here
Looking forward at fixing the Beogram 8002 cover, the picture here shows the 8002 cover hinge pieces (circled in red) and the 8000 hinge pieces. I decided that the cover that came with the 8002 is in good shape except for the hinge problem. As you can see in the picture, the decorative, black plastic hinge cover is damaged on the 8002. So I pulled that hinge assembly off the 8000 cover and will use it on the 8002.
This picture shows the Beogram 8002 cover assembly hole where the cover hinge assembly fits. The rectangular bar where the spring fits and what the hinge attaches mounts in here. the red line points to some clear tape where the hinge assebly slides. On the Beogram 8000 working cover hinge, I can see that clear rectangular pieces is smooth plastic so the hinge bar can slide easily. On my Beogram 8002, this area is sticky. The original plastic must have been removed and there is glue left behind. I plan to cut a matching piece of thin acetate and glue back in place there.
Well done Jon!
Just to confirm - did the DB Tester actually cause your good BG8002 to FAIL?
Or did it just give the same illumination as your bad BG8002?
With the 60W bulb, the dim bulb tester interfered with the operation of my good BG 8002 as well. I also tried a different 60W bulb and got the same result.
I cut a small rectangular piece of Dura-Lar (acetate substitute) and glued it in place where the Beogram 8002 cover hinge assembly travels. The Dura-Lar material is very slick and tough. It won't tear and it is thin. I also use it for shims when I replace speaker surrounds. I have sheets of it in thicknesses of .003", .004" and .005". I used .005 inch thickness here. Tomorrow evening I should be able to get the cover re-installed.
sonavor:With the 60W bulb, the dim bulb tester interfered with the operation of my good BG 8002 as well. I also tried a different 60W bulb and got the same result.
With some simple calculations, assuming you are on 120V (doesn't actually matter for the final result):
A 60W bulb @ 120V consumes 0.5 amps, equalling to a 240 ohm resistance. The Beogram (15W @ 120V) consumes 0.125A => 960 ohms.
Assuming the 15W for the Beogram means average consumption in operation, it will receive only 120V * (960 / (240 + 960)) = 96 volts, or 80% of the nominal mains voltage in steady state, and I'm sure it needs more than 15W while accelerating, dropping the mains voltage seen by it even further. I can't understand how the bulb in series could *not* interfere with it.
So, in conclusion I believe you can stop worrying about it - and congratulations for the good work
--mika
That's why I wanted to confirm whether the effect was the same on his other BG.
In practice however, I have not measured more than a couple of volts voltage-drop in the DUT - the last one I did was a BG4000, which had a drop of only 4V.
Furthermore, the voltage-drop calculation is good only if the lamp illuminates - if it is extinguished, there is no voltage drop at the DUT.
I did have a BG8002 on my bench about a year ago, connected to the DB Tester, and I do not recall seeing the large voltage variations which Jon described, so I was watching his progress very carefully.
Menahem Yachad:Furthermore, the voltage-drop calculation is good only if the lamp illuminates - if it is extinguished, there is no voltage drop at the DUT.
Yes, you're right the filament will have a much lower resistance when cold (I don't seem to have a single incandescent bulb left to measure ). It will also vary between different types of bulbs.
But, if the lamp flashes, it's going to drop the voltage arriving at the load and it might drop the voltages at the power supply secondaries as well. Linear power supplies are designed to work with a steady input, because any excess margin will be a lot of wasted electricity & heat during normal operation conditions.
tournedos: sonavor:With the 60W bulb, the dim bulb tester interfered with the operation of my good BG 8002 as well. I also tried a different 60W bulb and got the same result. With some simple calculations, assuming you are on 120V (doesn't actually matter for the final result): A 60W bulb @ 120V consumes 0.5 amps, equalling to a 240 ohm resistance. The Beogram (15W @ 120V) consumes 0.125A => 960 ohms. Assuming the 15W for the Beogram means average consumption in operation, it will receive only 120V * (960 / (240 + 960)) = 96 volts, or 80% of the nominal mains voltage in steady state, and I'm sure it needs more than 15W while accelerating, dropping the mains voltage seen by it even further. I can't understand how the bulb in series could *not* interfere with it. So, in conclusion I believe you can stop worrying about it - and congratulations for the good work
Thanks for that explaination mika. That helps a lot. -sonavor
chartz: A new thread is in the air!
A new thread is in the air!
New thread started.
Sorry for the intermittent threadjacking. Well done on the BG!
Rich: chartz: A new thread is in the air! New thread started. Sorry for the intermittent threadjacking. Well done on the BG!
No problem. As I said, I have a Beocord 5000 sitting in a box disassembled so I will be watching that thread with interest.
Tonight I re-attached the turntable cover. Note: In the second picture I experimented test fitting the hinge and spring with the spring from the Beogram 8000. I ended up using the original Beogram 8002 spring.
I attached the Beogram 8002 suspension springs tonight. There are three leaf springs that clip to wires on the floating chassis. In the picture here I show the spring clips in the top part of the picture. The clip with the triangular bend attaches from the bottom of the floating chassis. The clip with the two U bends attaches to the triangular clip, then to the leaf spring. Before lowering the 8002 lid assembly to attach the clips to the springs, make sure the U bends (that attach to the springs) are facing properly where the open end can hook over the end of the spring. When the U bend clip is perpendicular to the triangle clip, it will lock into place in the floating chassis and sit upright (as shown in the second picture). That makes the U bend easy to grab with needle-nose pliers when attaching to the spring. The bottom part of the picture shows the clip attached to the spring. As I said, there are two more of those spring and clip attach points for the chassis.