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
Now the Beogram operating smoothly
However, the Beogram is still not 100%. I am having trouble with the speed display. The smallest digit (Digit 4) starts flickering after the turntable is on for a while and sometimes goes completely out. I have checked the connection on that digit and even reflowed the solder points. But the problem remains. I might try swapping the display or control panel. I suppose there could be a problem with the transistor (IC6) that drives the segments of Digit 4. The strange thing is, the display didn't show any problem until everything was assembled (of course). It is going to be a pain to disassemble everything to get back to that board. You have to detach the suspended chassis in order to open the turntable and get to the circuit boards. The task has to be done though. At least I have most of it repaired. Running the Beogram through the commands on the control panel, every function appears to be working. Since using the grease that Martin recommended, I am not seeing any vibration in the turntable travel (forwards or backwards). So I am down to a small display segment in keeping this project from completion.
The Beogram can flicker the last digits to indicate that correct platter speed cannot be achieved.Is the platter speed correct and steady ?Can you tell a humming from the motor coils consistent with platter rotation if you listen closely withyour ear to the deck ?
Martin
When I was originally making the repair I could hear the motor trying to adjust speed and see the indicator segments flicker. That is a concern here with the Digit 4. Last night though, the Digit 4 was completely off and wasn't flickering. It is back on now though. I have a meter to check speed so I will hook it up and check it against what the Beogram is showing.
I checked the speed with a small digital tachometer I have but it only displays down to the tenths digit so for 33.33 I get 33.3 on the tach which is what the Beogram shows when Digit 4 is not displayed. I am going to work on getting another control panel and processor board installed to see if the problem is still there. That will tell me if the problem is in the display of the value or if there is a real speed control issue. I am not hearing the Beogram motor attempting to adjust the speed when the Digit 4 is out.
Probably one more cracked solder joint inside the processor casing then - or the display itself is at fault.
Here is a Beogram 8002 picture I meant to post earlier. Just an FYI - The service manual doesn't show this in the exploded view because it wasn't expected for the aluminum deck panel to come off. Under the aluminum deck panel however, there is a small spring on the left side. I guess it was for grounding. Maybe for anti-static? In any case, don't forget to put it back in place before resealing the deck with new double-sided tape.
Yes, it's for static discharge.
Tonight I switched the Beogram processor module back to its original module to see if there is a speed problem or if it is just a display problem. I already recapped and reflowed the solder joints on this module earlier, but it has a problem where segment "g" of all four display digits will sometimes illuminate and not go off.
At first the display looked like it would be good.
But after a few minutes, the "g" segment problem showed up.
I think that points to the driver IC as a possible problem because the pin 14 of that IC controls the "g" segment of all the digits.
One thing about this processor module though...Even though it has the segment problem, it doesn't seem to have the Digit 4 flicker so I think the speed control on this unit is good. Tomorrow I am planning on running over to Mouser and pick up some 7447 7-segment driver ICs (along with some other parts). I pulled the 7447 IC out of this module and stuck in a 16-pin IC socket. Doing that required re-soldering the connections on that IC. The problem with the "g" segments remains. So I am hoping a new driver chip will fix the problem. I checked the path on the related resistor (R25) and capacitor (C45). They were good.
I am cautiously optimistic in saying I think this Beogram 8002 is working normally again.
Stylus in the groove
What was the problem on the stuck "g" segment across all digits? It didn't turn out to be the 7447 driver IC. When I installed a new one, the "g" was still stuck on. So I pulled the R25 (68 ohms resistor) and C45 (4.7nF capacitor) and verified that makes the "g" segment go off across all segments. I should mention that I checked the BCD out from the processor and it was providing the correct signals to the display driver.
R25 measured within tolerance but C45 was almost 20% off. The service manual specifies 10% for those caps. I'm not sure if that was the problem but I replaced the C45 capacitor with one from my spare board. I had checked continuity on that signal earlier and it appeared fine. I had even reflowed the solder joints. After replacing the C45 and putting it (and R25) back in place, the display now works fine.Tomorrow I will continue with more testing of the Beogram.
I should mention that the last picture is of the spare board that I removed capacitors from. The two capacitors at the bottom of the picture are the ones I removed from the board currently in the BG8002. That module had different brand capacitors than this spare board.
What if replacing the cap just re-established a bad contact? I sincerely doubt such a component change would make any difference at all. But then of course, I might be wrong John!
Well done all the same!
Jacques
chartz:What if replacing the cap just re-established a bad contact?
I suspect it rather broke an extra contact - perhaps the upper end of the cap had shorted to ground through a tin whisker or something. I have never handled one of these boards, but it looks like the leg goes through a ground plane layer on the PCB.
Good job getting it working!
--mika
Well done!
//Bo.A long list...
tournedos: chartz:What if replacing the cap just re-established a bad contact? I suspect it rather broke an extra contact - perhaps the upper end of the cap had shorted to ground through a tin whisker or something. I have never handled one of these boards, but it looks like the leg goes through a ground plane layer on the PCB.
Yes, I am guessing that is what the problem was. I had reflowed those connections a couple of times so sometimes it is better to just pull the component, check it, and re-solder it back in place. I may do that with the spare board to get it back to working condition.
I was reviewing my pictures of the board and the repair steps and realized something. When I reflowed the solder connections on that small processor board, I only did the solder joints on the trace side. That board is a little tricky as there are a number of solder pads (as for those small 4.7nF caps that are on the component side. In those cases, that is the connection to ground. So I hadn't reflowed that side (they are kind of hidden) and I bet that was the source of the problem.
Good job!
Those older ceramics were well before the days of modern C0G (NP0) ceramic caps, which are highly stable at all temperatures. On oscillating-type circuits, I always replace the older ceramics with a new C0G type (Murata, TDK are very reliable). It's another step in preventing future problems.
When I resolder PCB's like this (with solder joints on the component side as well), I always wiggle each component to ensure that the solder penetrates the via completely. It is unquestionably more time-consuming, but I've probably saved myself countless hours in troubleshooting incidents like this.
The redeeming side of all this is that the vast majority of PCB's in vintage equipment are single-layer only. So, it's a problem which doesn't show up too often.
True. My favourite troubleshooting-repair so far has been the Beomaster's processor board.
So much that can go wrong on that one...
Thanks Menahem. That's good information to know.
I have one remaining nuisance problem on this Beogram I discovered while testing today. The switch that determines Stop and the stylus set down position appears to be causing a problem. Occasionally when I press Play, the tonearm doesn't travel all the way to the record and set down. So I press Stop, it returns to the rest position. When I press Play again, it travels all the way to the set down point and works properly.
I have sprayed some Deoxit into the switch and operated it manually about fifty times to work the Deoxit in good. It seemed to help at first but I am still getting the problem occasionally. I was hoping I wouldn't have to disassemble this Beogram again but I might have to open it and replace that switch. Have you seen that problem before?
On the bright side, with the Beogram 8002 playing records again, I was able to run a complete test of recording a record on the Beocord 8004 through the Beomaster 6000 (all part of this same set). The Beocord 8004 recorded beautifully and the restored MC120.2 speakers are also sounding great. So all I have left is the Beogram start switch intermittent problem.
When it fails to play, how far does the tonearm travel towards the record?
I will have to catch it in the act and take a picture but I believe the detector arm reaches the record when it stops. Currently, I just finished recording one side of an album, flpped the LP over, pressed Play and it set down perfectly. I think I will have to let the turntable sit idle a while for the problem to re-appear. But I will take a picture to show the exact position.
I waited about an hour and tried the Beogram Play. I get the problem again. The picture shows where the arm stops. Pressing Stop, then Play again resulted in correct operation again.
When I try the test again, I think I will manually toggle the switch a few times (with the Beogram unplugged) before pressing Play.
The last 4-5 mm or so up to the lead-in groove is travelled at a lower voltage (slower speed) and thetonearm is not lowered until the correct number of pulses from the threaded shaft opto has been reached.My theory is that the servo motor hasn't got enough power to do this with the lower voltage. This is usually causedby dust and dirt (or wrong lubrication) on the threaded shaft and carriage nylon bushing and/or a too tight servo belt.Can you measure if the servo motor has any DC voltage across it when the tonearm hovers like this ?
Another thing is the adjustments for the << and >> buttons.DC voltages are mentioned in the service manual, worth checking!
Dillen: The last 4-5 mm or so up to the lead-in groove is travelled at a lower voltage (slower speed) and thetonearm is not lowered until the correct number of pulses from the threaded shaft opto has been reached.My theory is that the servo motor hasn't got enough power to do this with the lower voltage. This is usually causedby dust and dirt (or wrong lubrication) on the threaded shaft and carriage nylon bushing and/or a too tight servo belt.Can you measure if the servo motor has any DC voltage across it when the tonearm hovers like this ? Another thing is the adjustments for the << and >> buttons.DC voltages are mentioned in the service manual, worth checking! Martin
Okay, so back to the bench with the Beogram. I measured the DC voltage at pins 1 and 2 of P1 of the main board. That is for the arm motor.I get the following measurements -Stby : 0vPlay : -7.4v until it stops and plays, then -0.3v (arm down)Play (when the problem causes it to stop short) : -7.4v, then it stops and drops to -0.06v (arm up)Note: That is because the arm doesn't try to drop into play mode. It is still in the raised position.
Arm RaisedStop : 7.1vForward : -3.6 to -4vFast Forward : -7.6vReverse : +3.6vFast Reverse : +6.6v
On the << and >> adjustment in the service manual, all I found was this procedure.
Does the manual want the voltage measurement between P5-4 and P5-6 or the voltage measurements from -
P5-4 to P5-3 (gnd)andP5-6 to P5-3 (gnd)
I am guessing it is P5-4 to 3 for one adjustment screwand P5-6 to 3 for the otherHere is the P5-6 to P5-3 measurement after my adjustment
Good news this morning. The first thing I did was pop on a record and press play. The Beogram went perfectly to the set down position and began playing. A few hours later and I repeated the test again with the same, good result. So far so good. I have the Beogram reconnected to the Beomaster 6000 system and will continue using it for a while. If nothing else happens, I should be able to give this system back to its owner. I enjoyed this repair as I was able to gain some more valuable information on restoring these turntables. I have a couple more 8002 decks waiting for me and one 8000 so I will see what issues they have and post anything this thread hasn't covered.
As said, good news!
Yes indeed. I would like to thank Martin again for sourcing parts and sharing his repair experience. I really appreciate it.
It's Phil, and I'm connecting some dots.
I hadn't seen this thread until your link to it about the grounding spring on Rajod's 8002 thread. And I bet I know you from VE and you have a PX-2 Yamaha as well? And we both nibbled on a PX-1 that left a bitter taste in my mouth? You're in Oregon? I'm in NJ
How can I get either a printed or digital copy that you mention here? I am going over my VE printed copy which resembles the Beo copy (in that much is illegible or barely so) and copying from yours some of the "cues"
And, I haven't completely read through all, but I bet it's in the processor can! I was just coaching Rajod to set up an 8002 "test bench" so he could substitute known good parts and verify things. Seems every time i go on a wild goose chase, it's the processor.
And, I am awed by your diagnostic skills and determination! These threads remind me of the two 8002s and one 8000 I should finish up and sell!
This IS a great read!! I'm up to pg 13 now.
Pg13/Dillen:
"The Beogram 6006 and 8000 CPUs are interchangable.The 8002 is not.Apparent differences are that it supports the two little arrows on the sensor arm and it hasa different coding to support multiple play repeats but there are other things too."Don't expect it to work and - to be on the safe side - don't do it. Those CPUs are quite sensitive and not too plentiful."
I have swapped an 8000 processor can into an 8002 and, except for losing the multi play and pause differences, all has been good for years (after reflow and recap including processor) I sold it recently; perhaps the arrows in the sensor arm didn't light-I don't recall, but expect I would have noticed. I do believe that one CPU leaves the arm parked/paused for a good while, then returns it to the garage and shuts off; pressing play re-starts it and it goes back to the point it was paused at and drops there-nice! And I think the other just remains paused a long time, then shuts off?? But am not certain-maybe it pauses forever?
I have not had the courage to swap the 40pin micro-controller from 8000 can to 8002 can..... But I'd love somebody to do so and report.