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
The plot thickens...
I still think that there must be a solder bridge somewhere preventing normal operation. Have you inspected everything under a magnifying glass, with the PCB layout to compare to?
The more you test, the more you seem to find that components are good. Mind you, semiconductors may have the strangest behaviours under power and report normal characteristics when tested.
I'd take some time to check the PCBs again, for what it's worth!
I am keeping a bottle of champagne in the fridge.
Jacques
And that's French Champagne, mind you.
None of that funny American imitation stuff
chartz: I still think that there must be a solder bridge somewhere preventing normal operation. Have you inspected everything under a magnifying glass, with the PCB layout to compare to? I'd take some time to check the PCBs again, for what it's worth!
I feel pretty confident that the solder points are good on PCB1. They have been resoldered. The one component on that board (other than the electrolytic caps) that needed replacing was TR6 and that was because it had a broken base lead. But I'll just have to keep digging and see. At least I know that the problem is within a certain area related to the P4 connector. The other problem I am seeing is the display segments after the 8002 warms up. On that one I am thinking it is a heat issue in the PCB2 container. I am planning on looking at that last since it isn't affecting the control of the turntable.
-sonavor
Finding components that fails under power is a PIB, you work your but off, checking everything cold, and then run into failures like this, go on John, I will not take out the champagne when you finish, but I will enjoy a good mixed Rum and Coke with a lot of ice.
I enjoy your reasoning and explanations, Agathe Christie or Hercule Poirot couldn't do it better.
Collecting Vintage B&O is not a hobby, its a lifestyle.
If a fault is occurring sporadic and/or seem to be temperature related a hair dryer or a hot-air gun and cooling spray might help to localize the problem.
//Bo.A long list...
I continued with some additional dim bulb testing of the drive circuit. From my previous testing, I know that disconnecting the wire at P4-4 results in the dim bulb test passing (bulb remains off when power is applied). I resoldered the wire for P4-4 and removed the wire for P4-3. That also results in a successful dim bulb test. I resoldered the P4-3 wire.
The next thing I tried was to see if the path from P4-3 over to R113 and TR33 was a problem. I decided to remove D39 and D40. Applying power and testing the Play resulted in the dim bulb test failing...the bulb illuminates when I press Play and returns the tone arm to the start position. So it appears that the path from P4-3 over to OL1 by way of R113 and TR33 are not part of the problem.
Going the opposite direction, I removed the wire that goes from P7-11 over to R106, R107 and P4-3. That resulted in a successful dim bulb test again.
So the problem does appear to be with chassis components OTR2, OTR3, OD1, OD2 and PCB1 components D37 & D38 (47V zeners), capacitor C42. Here is a picture of the circuit area I am looking at.
From what you show, I would look at R113 and the BD240, and the inter-PCB connectors and solder bridges.
Menahem
Menahem Yachad: From what you show, I would look at R113 and the BD240, and the inter-PCB connectors and solder bridges. Menahem
With D39 and D40 removed R113 and BD240C shouldn't have any affect, right? Earlier in the project I removed and resoldered the PCB1 connectors, including P4.
sonavor: Menahem Yachad: From what you show, I would look at R113 and the BD240, and the inter-PCB connectors and solder bridges. Menahem With D39 and D40 removed R113 and BD240C shouldn't have any affect, right? Earlier in the project I removed and resoldered the PCB1 connectors, including P4. -sonavor
I decided to rethink this. Something didn't make sense in my testing and what I am seeing. When I remove the path to the (c) side of the 30 VAC transformer secondary, the dim bulb tester doesn't light up when I press the Play button (starting the turntable). Earlier I checked out the chassis components OTR2, OTR3, OD1 and OD2 - they measured good. So I started thinking about the dim bulb test I am running - I press play, the tonearm moves to the play position, the dim bulb tester illuminates while the arm moves, cancels the Play operation and the tonearm returns to rest, the dim bulb tester lamp goes off.
Maybe that test isn't valid because I am trying to test the play button with PCB1 - P4 connected (drive circuit) but the inner turntable platter is not installed. I think that the 8002 logic is moving the tonearm to play position but it isn't getting any feedback indicating the turntable is rotating (because it isn't). In that case does it keep trying to drive the platter and that is what is causing the dim bulb tester to illuminate? Does P4 (drive) connector need to be disconnected when testing without the platter?
With the wire for signal (c) reconnected, I installed the inner turntable platter and tried the test again. This time the dim bulb doesn't illuminate as I press the Play button and the turntable rotates. I tried both 33 and 45 successfully. This 8002 performed like this before (right after the recap) but then started rotating the turntable platter in the opposite direction after being on (in standby mode) for a while. It is too late tonight to retest that condition so I will do that tomorrow. I expect there to still be a problem as I haven't repaired anything in the drive circuit other than resoldering connections. At least it appears that I have a starting position that I can make some measurements to compare to if/when the turntable messes up.
I don't want to be a pain in the neck, but I had a 8000 behaving like that and there were two problems. A bad solder at the motor connector and a tiny crack on one of the tracks leading there (I can't remember which one, I should have posted here! - hence the value of your work John).
chartz: I don't want to be a pain in the neck, but I had a 8000 behaving like that and there were two problems. A bad solder at the motor connector and a tiny crack on one of the tracks leading there (I can't remember which one, I should have posted here! - hence the value of your work John).
Today I plugged the Beogram 8002 in (through my variac and dim bulb tester) and just left the turntable in standby mode for a while (about and hour). It stayed in that state without any problems...the platter didn't start turning on its own like a couple of weeks ago. Next I ran it through some commands: Turn, Play, Fast Forward, Reverse and Stop. Everything seemed to work fine. No flickering of the dim bulb tester at all. I left the turntable in standby again for quite a while and observed no odd behavior. Next, I used the Turn button to start the platter rotating and left it like that for about 20 minutes. Again, no problems.
Finally, I started getting some minor flickering on the dim bulb tester when I tried to use the Play button again. It only briefly flickers but it does none the less. So it appears there is still some problem in the drive circuit. Starting from a Stop (standby) position, pressing the Play button should result in the 8002 logic to look for a 33, 12 inch LP, then switch to 45 looking for a 7 inch single. Part way into the search for a 12 inch, 33 RPM LP, the 8002 stops and returns to Stop. The problem appears to be with the turntable attempting to change speeds. At the beginning of the Play there is sometimes a flickering of the bulb as it starts out at 33 RPM, then again where the 7 inch record should be detected (and speed changed). I can override the auto-Play and use the fast forward button to move the tonearm to the full range of travel. When I am consistently seeing a flickering of the dim bulb tester lamp is on the speed change. So if I just start the turntable with the Turn command, I will see a flicker of the bulb when I push the 45 button. I also hear a slight (and very brief) electronic hum when the speed attempts to change. The coincides with the flicker of the dim bulb lamp. It is like the motor is groaning to change. Maybe it is a problem with the electronic braking?
I have a Beogram 8000 parts unit now. There are some duplicate parts in that turntable that I should be able to swap out in my 8002.
Jacques, when you refer to the motor connector, are you talking about the PCB1 P4 connector?
For anyone that hasn't used a dim bulb tester, here is what mine looked like when I was testing with PCB1 P4 connected a week ago. Note that my current problem with the bulb flickering during speed changes is much dimmer that what was the case when this picture was taken.
P4 yes, that's the one. Now can you show a picture of your P4 please?
The groaning or humming at speed change seems normal to me. So the processor sends a reset signal at the speed change attempt? Does the speed detector do anything here?
chartz: P4 yes, that's the one. Now can you show a picture of your P4 please? The groaning or humming at speed change seems normal to me. So the processor sends a reset signal at the speed change attempt? Does the speed detector do anything here?
Sure. Here is a picture of the PCB1 trace side and connectors - P3 and P4.
After some additional testing I believe the problem is within the drive circuit path and relates directly with the motor drive attempting to increase speed. When I start the platter turning using the Turn button I will often see a very faint flicker on the dim bulb tester. By flicker I mean the bulb illuminates briefly then goes off. As long as the platter keeps turning or returns to Stop, there are no more incidents with the tester bulb. If I press the 45 button, I also see a faint flicker. Pressing 33 again doesn't cause any problem.
When starting from the Stop (standby) position and pressing Play, I also see a flicker on the dim bulb tester. That illumination is usually brighter. After a few tests of that condition the problem appears to get worse where the flicker gets as bright as in the picture I posted previously of the bulb. Pressing the fast foreward or reverse buttons don't affect the problem.
Can I see a bad solder joint at pin 3 or is it an optical illusion?
Here is another picture of the OTR2 and OTR3 portion of the drive circuit that is on the Beogram 8002 chassis. The technical description document for that says OTR2 and OTR3 function as variable resistors in series with the transformer and stator. I would like to swap out the small board that has OTR2 and OTR3 with the one from my Beogram 8000 parts unit. In my earlier trouble-shooting I found that disconnecting either the wire going to P4-3 or P4-4 will result in the dim bulb not illuminating. I realize that removing either of those wires prevents the turntable from working at all but when I leave those wires in place and remove diodes D39 and D40 (preventing the down stream path of the P4-3 wire from reaching the brake), the dim bulb still illuminates. So I think the best candidate to try next is to replace the OTR2 and OTR3 board. I'm not sure if that is easy or not. I don't see an easy way to remove and replace that small board.
chartz: Can I see a bad solder joint at pin 3 or is it an optical illusion?
P4-3 ?
sonavor: chartz: Can I see a bad solder joint at pin 3 or is it an optical illusion? P4-3 ?
Yes. What is it, between the two power transistors?
chartz: sonavor: chartz: Can I see a bad solder joint at pin 3 or is it an optical illusion? P4-3 ? Yes. What is it, between the two power transistors?
This picture shows P4-3. It looks okay but I will check it again.
And adjacent to the tachodisc, the joint above the number 6 engraved on the PCB. Below the ITT 1N400x, there are 4 solder points in a row. Look at the 3rd joint, how the copper wire is soldered onto it.
Menahem Yachad: And adjacent to the tachodisc, the joint above the number 6 engraved on the PCB. Below the ITT 1N400x, there are 4 solder points in a row. Look at the 3rd joint, how the copper wire is soldered onto it.
You are referring to this part of the picture. The third solder pad has no wire connected to it. The Stator 4C1 wires connect to the first, second and fourth pads.
And this one
On that picture the brown wire and the blue wire are where I disconnected the signals (P4-3 and P4-4) to help isolate the problem. I have verified in re-soldering them that those connections are good. They just aren't pretty. What I would like to do, if possible, is replace that whole small board (and components) with one from my spare BG8002.
I suppose the easiest thing to try next is just to rework that OTR2 and OTR3 board - resolder everything and replace all of the components.
I figured out that all I had to do to remove the drive pcb was to slide it out of the plastic clips towards the center of the turntable. With the small drive pcb removed I replaced it with the drive pcb out of my spare Beogram 8000. The BG8000 is a non-working turntable that I got as part of a whole 8000 system (none of the 8000 system pieces are in working order). I plan to use this Beogram 8002 in its place.
With the drive pcb replaced on the chassis, I repeated my operational tests.....same result. So it would appear that the problem is with the drive circuit back on PCB1.
While I had the parts BG8000 turntable open, I decided to try the transformer from that unit in place of the one I have been using with my 8002. The startup problem was worse with the BG8000 transformer.
By worse I mean that with the transformer from the 8002 I can press Play (from the stopped/standby state) and have the tonearm travel all the way to where it reaches a seven inch record. At that point where it needs to switch to 45 RPM, the dim bulb tester flickers and the tonearm returns to the start position. Also, I can press the Turn button and the platter will turn.
With the transformer from the BG8000, pressing Play or Turn will result in a larger flicker on the dim bulb tester and the platter will only try to start, then immediately stop.
Transformer to PCB1 connector pins P7-5, P7-11, P7-12 and P7-6 are directly involved with the drive circuit. Of course other transformer pins provide the source for the positive and negative 15 VDC as well as +5 VDC. The positive and negative 15 VDC are used on the IC3 preamplifier of the drive circuit. The +5 VDC is used in the brake circuit. From earlier tests, I don't think the brake circuit is causing a problem.
I will recheck the wiring for the power to the drive circuit including the wiring from the transformer (P7) to the drive circuit. I will also start looking at the drive preamplifier section - IC3 (pins 1, 2, 3, 4, 8), TR27, TR28, TR29 and TR30 ...and related components.
I tried a couple of easy tests this afternoon. A quick thing to try on the driver circuit was to swap out IC3 on PCB1. It is an LF353N (dual JFET Op Amp). It was worth a try but didn't fix the problem (or even change the result). Tonight I am planning on attaching some test leads to the drive circuit so I can monitor the signal on my oscilloscope.
Another thing I tried today was to pop the metal top off the PCB2 box. I wanted to see if more air flow would affect the nuisance display problem. That result was the same as well. Several minutes after power is applied (plugged in), the extra display segments light up. So I'll replace PCB2 IC2 (SN74247 7-Sement Decoder).
Mmm... Still holding my breath here!
When you finally find the fault (s) we will be left with an extraordinary lesson John!
A lesson about patience and pugnacity too.
I'm waiting for the lessons everyday, the details, pics and explanations makes this thread even more interesting.
Man, this is a great thread to follow. Very inspiring. Almost makes me want to get the 1970s BC5000 out of the attic and try again!
Almost.
I really ought to give that thing to John or Soren....
Rich: Man, this is a great thread to follow. Very inspiring. Almost makes me want to get the 1970s BC5000 out of the attic and try again! Almost. I really ought to give that thing to John or Soren....
I have a Beocord 5000 that I bought back in 1977. It is disassembled in a box waiting for me to get to it. Unfortunately I have a bunch of projects to get to first. :)
I should add that the Beocord 5000 is a really nice cassette deck.
sonavor: I should add that the Beocord 5000 is a really nice cassette deck. -sonavor
The reason why I've got two working!
Rich:I really ought to give that thing to John or Soren....
I have a BC 5000 pizza box, and is very happy with it, but a BC 47XX will fit nicely to my, still in the workshop, BM 4400.
So, as John already have one, Rich, I'm open for suggestions, with backups like Jacques and John nothing can go wrong,
Søren Mexico: Rich:I really ought to give that thing to John or Soren.... I have a BC 5000 pizza box, and is very happy with it, but a BC 47XX will fit nicely to my, still in the workshop, BM 4400. So, as John already have one, Rich, I'm open for suggestions, with backups like Jacques and John nothing can go wrong,
If you want my Beocord 5000 Type 4716, it's yours. Send me the McAllen address via PM.
Rich:If you want my Beocord 5000 Type 4716, it's yours. Send me the McAllen address via PM.
Rich, you have a PM, thank you very much, an interesting project, I will do my very best.
When you have it, please let pay at least packing and shipping costs.
A new thread is in the air!
chartz: A new thread is in the air!
Oh yes, just got confirmation from Rich, but first I will have to finish the BM 4400, but the last week I was hit with a lot of work, and upon that Montezuma's vengeance.
sonavor: Tonight I am planning on attaching some test leads to the drive circuit so I can monitor the signal on my oscilloscope.
Tonight I am planning on attaching some test leads to the drive circuit so I can monitor the signal on my oscilloscope.
I connected my scope probe 1 to the drive signal between R104 (180 ohms) and P4-4. I connected my scope probe 2 to R106 (330 ohms) on the side that goes to (c) - which is the transformer pin P7-11. The pictures here are from the oscilloscope. The first one is the Beogram 8002 at rest (standby). The second one is with the platter turning .... after it is settled.
This picture shows what happens when the speed changes from 33 to 45. I am not able to set up to catch the beginning of the transition from the steady turning to the acceleration but this picture is during the transition. Notice that the AC voltage from the transformer pin P7-11 (c) dropped to zero volts. That is when the dim bulb flickers. The same thing happens when starting from standby mode to play. Sometimes the speed transition is too severe of a load and the turntable immediately stops. Sometimes it is just a faint flicker and can continue on to the play position.