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
Hello all,
I have had a BG8002 as part of my 8000 system for about 4 years now I think. Unfortunately it started acting up some time ago: not starting, showing 33 as soon as I plugged it in, just erratic behaviour pointing to the common problems of bad caps and or connections.
Some caps were already replaced by the former (very knowledgable) owner. I replaced the rest of the old caps. I resoldered and cleaned the connectors on main and processor PCB and every other bad looking joint. Worked fine for maybe a day and then went wonky again!
Resoldered lots of connectors again, replaced 5V regulator as it gave 4,8V instead of 5V. worked for a day and went whacko again!
Replaced the processor IC socket. Worked for a few days and then the bad stuff started over again.
I suspected the 'bare wire into socket' connectors of the processor can and keyboard-to-main pcb connectors. Replaced them with more sturdy new connectors. Again the BG worked fine for a few tries and... then the erratic stuff started over.
I'm going slightly mad now. What shall I do? Inspection under magnifying glass did not show any broken traces but could have missed something.
My differential diagnosis:
- bad soldering or broken trace or shorted solderings somewhere that I have missed
- bad 4n7 ceramic on the processor board
- bad microprocessor IC
My questions:
- How can I check if the processor is fried? If this is the case any soldering will be for nothing.
- What should be my next step? I've opened the BG up one too many time and can't really see clearly anymore.
Any suggestions or moral support would be greatly appreciated!
You will have to ask Martin for sure but in the several Beogram 8002 turntables I have restored the processor hasn't been a problem. If you replaced everything else and you couldn't get anything to function (and power supply is verified as working), then maybe the processor would be suspect. However, I think I understand you saying that the turntable will function properly at times so that doesn't sound like a processor problem to me. If it was fried nothing would work. You will probably need to set the board and control panel in a position to function without installing them into the turntable chassis in order to trouble shoot some signals. For instance, when it won't start, you will be able to probe signals and isolate where the fault is originating. if you can post some detailed pictures of the work you have done so far, other members that have done these restorations can double check your work. I know on one of my Beogram 8000 restorations recently, Beobuddy was reviewing my work and found I had a capacitor connected wrong. It's very helpful to have a second set of eyes look at your work.
One question to clarify the symptoms - Every time you do some work on it and then try it out you say it works correctly for a while, then starts failing. How long does that take before failures occur? Also, if you unplug the turntable and let it sit for a while (few hours to a day) after it has started failing, will it work for a while again when you plug it back in? I ask that to determine if the problem could be temperature related. Maybe there is some hidden, cold solder joint somewhere that is causing the havoc. Another thing to consider are the actual connectors. You resoldered the board connectors but the wire harness plugs could have a loose connection somewhere. Those can cause all sorts of strange behavior. I had a Beomaster 8000 problem before where I started down the path of suspecting some transistors on a board but the problem was actually a bad pin in one of the wire harness plugs. It was an intermittent type problem so it wasn't easy to find. A lot of the time it turns out to be a simple low tech problem like that.
-sonavor
Hi Sonavor, thanks for the answer!
The time it takes to fail differs greatly, it doesnt get better when it has been standing.
Unfortunately I haven't had time to work with the BG till today. I've been measuring and reading your BG8002 thread.
The problem now is the table turns on, shows the red dot, the buttons work, but won't start the TT, just change the display. No response from platter or arm.
When I measure pin 4 of connector 6 (on/off signal) I get 0.736V when off, it becomes 0.711 when on.
The 5V is present. There is on pin 10 of P2 23.5V, on pin 8 there is 23.6V. There is -23.5V on base and emitter of TR19, 0V on the collector so the voltages from the rectifier are there.
The base of TR6 has 0.64V. Its collector has 0.100V.
The collector of TR21 has 0.053V when on, 0.100V when off.
TR23 had on its base 0.100V. On its collector 0.53 when off, 0.100 when on.
Comparing to your schematic and measurements I'd say TR21 is suspect. What do you think?
Examine the solder joints on those transistors. If you suspect TR21, desolder it and measure it outside the circuit. Before you do that though...what do you get for DC voltages coming out of the power supply circuit? Do you have +15 VDC across C28 and -15 VDC at the junction of D26 anode and TR19 collector? Measure those voltages for "Play" and for "Stop".sonavor
The +/- 15V are not there whether play or stop, something is blocking the power supply regulators from coming on.
I tested TR21 in my transistor tester, B=224, Vf=635 which seems fine to me. TR6 and TR19 also tested good. I could test the others later.
I measured +5V on P6-3 when on and +4.9V when off, the pin connected to 'reset' on the processor. Should this pin be 5V under all circumstances?
It has been quite a while since I went through the power supply signals so I would need to go through it again to properly diagnose your problem.
You said the standby light illuminates and the control buttons work. How do you know they work? If the unit won't turn on it sounds like the buttons may not be working. Have you double checked that the control panel cable hasn't come loose out of the main board (push in) connector it goes to? Also make sure none of those wires were bent or went into the wrong socket.
When you monitor P2-2, does it always have +5 VDC ? When you monitor the base of TR21, do you see it switch from a low value to around +5 when you operate the turntable to Play? You might try disconnecting the connectors from the main board, like the platter (P4 I believe), and see if you get +-15 DC power to come up.
sonavor
Mostly when I plug the BG in the display shows the . and when I press play it says 33 (not 33.33, only the first two digits show). This is what I call 'on'. I can change it to 45 with the 45 button. No respronse from the << or >> or other buttons but this makes me think the buttons are connected.
After a while the display dims out. sometimes when I plug it in the display has . . . displayed. There doesn't seem to be a pattern.
I replaced the push in connector of the buttons with a normal connector because the wires were very bent and wouldn't stay in.
The 5V is always present on P2-2 and P6-1 (it's actually 5V at the regulator, 4.98V at the pins)
Disconnecting all plugs except P2 doesn't make a difference in the +/-15V supply coming on.
TR21 switches from 0.74 when 'on' to 0.72 when 'off'.
Thanks a lot for thinking with me Sonavor! Your website was a great help to me when I replaced the caps on my MS150.2's.
I am happy to try and help. I dug up my old notes on the Beogram 8002 and I had a simulation circuit I did for the +-15 VDC power. If my simulation is correct, here is what the "On" condition is for the +-15 VDC.
Here is the "Off" condition.
As you can see, your P6-4 (base of TR21) always at 0.7 VDC keeps the +-15 VDC power supplies off. My simulation isn't accurately showing the +15 VDC in the "Off" condition because the capacitor, C28, actually should have a load so it discharges when power is turned off. I reworked my simulation below.With the P6-4 disconnected, what do you measure on the processor side?
I re-executed my simulator for the "Off" position and the +15 VDC does eventually start dropping. I realized my simulation circuit needed some sort of load resistance on the +-15 VDC outputs to properly show the way the supply works. Here is the "On" condition with dummy loads on the +-15 VDC outputs.
...and here is the simulation of the "Off" condition. Both the +-15 VDC outputs should turn off.
I think that means you need to look at the P6-4 signal disconnected but measuring on the processor side of the signal to see if it is operating. sonavor
I disconnected P6-4. As soon as I plug in the BG it has 4.88V on P6-4. When I press play it goes to 1.22V, stop and it goes back to 4.88. The BG will operate for about 5 seconds this way, then won't respond at all showing various nonsense in the display, or nothing.
The resistance I measure from processor pin to P6-4 is 3.24K, corresponds nicely to R11 so the trace and resistor seem fine
I think there is something going wrong inside the can. Maybe I'll change the electrolytic capacitor (gets hot in there I guess), and maybe I'll check the 4n7 caps, I read you found some faulty ones.
And not to forget, thanks for the explaining diagrams! That seems like some very handy software you are using.
Premiumverum: And not to forget, thanks for the explaining diagrams! That seems like some very handy software you are using.
I used National Instruments MultiSIM. There is a free version of that software available from Mouser called MultiSIM BLUE but I haven't tried that one yet. You should take a look at it. Note: On the yellow probe information text in the drawing I should have removed the parameters not needed. I left them at the default which is to display everything. Where I am probing for the DC voltage and current I should have set the probe result to only show those two parameters.From your latest test results the processor is sending the right control signals to the On/Off transistor TR21. That makes me suspect TR21. It may test out good with a transistor tester but fails during operation (under the load of the Beogram circuit).
I replaced TR21. Unfortunately it made no difference.
I still think something is wrong inside the can.
I took out C28 but it measures good. 46.7uF and 1.4ohm. I'll replace it just to be sure, it was an 85 degrees type.
So to recap where you are on this...The On/Off signal from the processor appears to work when it isn't loaded by TR21 but when TR21 is connected the base of TR21 just stays at around 0.7 volts (keeping the 15 VDC power supplies off). Can you remove TR21 and verify that the base would receive the On/Off signal from the processor? The reason I ask is because you checked the processor signal earlier by disconnecting a connector. I would like to verify the On/Off from the processor functions normally with everything connected (except just TR21). If it does function correctly that way then I would start thinking that the processor is unable to drive that signal low and maybe the processor is suspect. Check out C15 and R11 first though (including their solder connections). On a couple of my Beogram 800x units I had some problems with those small capacitors inside the metal box. One other thing...inspect the processor leads going into the socket and make sure a pin didn't get bent somewhere along the line.
I finally got round to working on the BG again. Checked processor leads, checked connectors on the can.
I replaced C28 in the can, I had already removed it last time for testing its value. This changed everything, I think for the better! BG starts with the red dot and responds to buttons, drives the arm and platter looking stable with correct display. This makes me think the PSU and on/off from uP are OK. However, not all is well yet...
New symptoms
When play is pressed the arm drives in but never stops. It goes all the way across, the BG does not switch to 45, the motor keeps running when the arm has reached its ultimate position. Pushing stop makes it return to base, the motor does stop there and BG goes back in standby.
The BG can manually be switched to 45, this will make the platter spin faster.
Records on the platter are not detected, the arm behaves the same with or without record.
The arm responds to << >> and play. The arm can be moved onto the record with << and >> and will then sink down on the record when pressing play. The arm will move tangentially with the grooves for half a minute, after that it stops as if it has reached the end of a record and goes back to standby position.
What changed?
I'm still having the BG turned on to test stability, but maybe the first issue is now solved. Maybe either C28 was bad (was rather high voltage spec, about 50V. I read bigger caps sometimes get 'lazy' doing low voltage 5V work) or maybe a connection on C28 was bad and now the processor is stable again.
What now?
For the problem that remains my differential diagnosis is as follows, in order of likelihood:
- P2 connector was changed by me, maybe made a mistake. Counting of the worms rotations happens through there so quite likely to cause the running arm.
- maybe bad adjustments make the BG not read the ribs on the platter. The detector and pickup arm were adjusted by me somewhere during the repair process because they seemed misadjusted somehow. Probably just had everything wrong because both are now too low. If the BG proves stable I'll do adjustments, will be necessary anyway if I get everything working again.
- If C28 was bad, maybe some of the other caps replaced by previous owner are bad. Might replace them all.
Questions:
Do these symptoms point to another specific place for the problem? Am I on the right track? Any other/better suggestions on where to look?
Of course I could still be seeing one of those intermittent 'it seems to be working again' moments now. Keeping thumbs crossed...
Hi,
Have you checked the surroundings of the OPE1
I had this problem (on a 8000) (the carriage going on and on forever). On mine, the cause was a burnt IR led in the OPE1. If I remember correctly, at each turn of the lead screw, the IR led "shines" on two phototransistors. Depending on the order the signals are sent to the microprocessor, the machine knows if it's going forward or back. This is also what makes pausing right in the middle of an album, possible (the machine goes back to it's resting position and then, if play is pressed again, the carriage return exactly were it was)
When the IR led is burned, the microprocessor does not count anything, thus, when play is pressed, the symptom described is possible.
When you say that the arm move tangentially with the grooves for half a minute, do you actually see the lead screw turning? If not, that's the reason why the machine stops. If it does turn, and the OPE1 is deffective, the microprocessor won't see any movements from it so it will stop anyway (this is an assumption). Perhaps a safety trick for skipping records!
The OPE1 (with the IR LED and the 2 phototransistors) is right behind the motor, in the upper right corner.
These are assumptions based on my sole (but successful) attempt in repairing thes decks :
http://archivedforum2.beoworld.org/forums/p/7246/64676.aspx
Guillaume
Hi Guillaume, thanks for the suggestion! I remember reading your thread before when doing research, I'll look in to OPE1 because I too once had some sparking at P2 testing for shorts....
Unfortunately when I did a quick plug in of the BG this morning, everything was back to square one. Only 33 appeared, sometimes 33 2. No response from buttons. My fiddling with the cpu can seems to have temporarily restored some connection that is now gone again.
I'll check OPE1, connector P2 and then get back to testing the signal going to TR21, can imagine the problem lies there. After that it's back to the uP can checking all connections again...
Today I went back into the BG. I took a peek inside the microprocessor can to see where I'd start and saw... a broken solder on one of the legs of X1! I resoldered. This explained things too well so I immediately put everything back and started the BG... presto, contact! Could this have been the issue all along? How have I been so blind!?
I'm back to test mode for now, time to see if everything is now solved for good.
The problem with the not stopping arm assembly remains, OPE1 is the suspect. It looks different from the one in your post, it has a red plastic body instead of clear. With the BG running there is 4.95V across it. I tested the LED with the diode tester, it is open in either direction... I'd say that means it is fried!
I hope my local electro shop has a replacement. Could this be the last step to getting the BG working again? Friday I'll have time for some shopping and soldering.
There you go. With my repairs I have seen cases where components have failed and need replacement but so many times the problems are just from broken connections. It is always best to check the connections first as those are the easier and cheaper to repair than new parts. With the arm assembly problem though...Yes, it does appear to be a case of a component (OPE1) problem. As Guillaume's post says, Martin should be able to provide you a replacement for that part.-sonavor
After some thorough testing I think I can safely assume the BG has been fixed.
Next to the bad connector on the crystal I found a bad connection in the pin that connects the ground from the component side of the PCB to the solder side. It caused the uprocessor to sometimes not turn on.
Thank you very much for the help and encouragement! On to a next project, what will it be?