Beogram 8002 dead after adjustment

[radman]

Brand new to the forum but not new to B&O.  I had a Beogram 8002 for years but it didn’t survive a lightning strike and was sold off for parts.

Some years later, missing the aesthetics of the 8002, I purchased a partially working unit in hopes of repair.  I recapped everything and reflowed at least 30 solder points, many of which were obviously cracked.  Most of the functions worked but the tonearm seemed not to sense position and a record would play for only about 30 seconds before stopping…

As part of the standard service I attempted to adjust the A & B screws for << and >>.  Voltages at pin 4 of P5 and pin 6 of P5 were about 770mV instead of the recommended 620mV.  I turned the unit off, adjusted each screw no more than a degree or two and now the unit is absolutely dead… not even a red dot on the display.  What happened?  It did not blow the power supply and no burning or popping.  Zapped the microprocessor?  I am essentially at the end of my knowledge to troubleshoot this… just when I thought I was accomplishing something.  Any suggestions would be greatly appreciated.  Radman.

[filip_kbh]

Have you tested the fuse?

[radman]

Yes.  Even changed the fuse for what that’s worth.

[sonavor]

Adjusting the forward/reverse LDR sensor sensitivity (for 620 mV) wouldn’t zap the microprocessor.  It is more likely that a cable/wire came loose or some other board trace cracked.  Those LDR adjustment screws can be a pain.

When a Beogram 800x project gets to this type of situation it is best to focus on the power supplies again.

Verify that you have the supply voltages from the transformer to the PCB 1 destinations.  Check the voltages on the three largest PCB 1 capacitors for the respective pre-regulator voltages (+24 VDC, -24 VDC and +13 VDC … or close to those).
From there, assuming those voltages are good, check the output of the +5 VDC regulator and the +15 VDC regulator.
If you have +5 VDC on PCB 1 then  it is a good guess that it is not making it to PCB 2 (where the microcomputer IC is).
The twenty pin ribbon connector between PCB 1 and PCB 2 can often be a problem.  Especially if the pins in the PCB press-to-fit connector do not mate well.

I happen to be finishing up a Beogram 8002 restoration now.  You can take a look here.  The posts are in reverse order (most recent first).  The power check post is here.
That Beogram 8002 had a few of its own moments when connector pin issues were preventing proper operation after the electrical restoration work.  That is typical of a Beogram 800x turntable though.

I would expect your Beogram 8002 to be okay…once you find the failed connection.

-sonavor

[radman]

Fantastic help!!  I’ll also see about removing the keyboard and checking the traces.

I haven’t tried to remove the keyboard for fear of breaking something.

[sonavor]

Be careful with the keypad.  I run into a lot of those where people have broken off the plastic tabs that hold the front plate with the keys tight against the keypad board.

The keypad boards haven’t been a problem area very often either.
The LDR devices can sometimes fail and the lamp can burn out but they aren’t usually a problem.

Check the press-to-fit, small ribbon connector that goes from the keypad assembly to PCB 1.
That is another problem area like the press-to-fit connector for PCB 1 to PCB 2.
…But start with tracing the Beogram 8002 power supply voltages first.

[radman]

With your help I have made some progress.  I had power to the main capacitors but intermittent 5V to the PCB23 cap.  Someone had already done a recap but this capacitor was loose,  After replacement the unit fired up!…

However, functions are not normal.  It does not recognize a record edge and thus travels all the way to the end and gets stuck. Manually backing the tonearm with the worm drive will release it and allows for <>, play and  stop functions but I cannot get a voltage at pin 4 or 6 of P5 at all.

Seems encouraging at least.

Probably stupid question… the short shielded black cable extending from PCB2 to a pin next R12 on PCB1 was broken.  The shield and internal wire derive separately from PCB2 but where would the shield go?  I attached only the internal wire… just don’t know.

Thank you for your help!

John M

[radman]

Obvious typo above: PCB2 not PCB23.

Finally able to set close to 620 mV for <>.  Beyond that, live to fight another day.

[sonavor]

Just the center wire of the shielded wire from PCB 2 connects to the single, terminal post on PCB 1.

Your other problem with the position detection not working sounds like either the position sensors are not working or not reaching the microcomputer board on PCB 2.

This post has some oscilloscope photos I captured of those signals for reference.
Occasionally a sensor device fails but I always suspect the wire connections first on these turntables.

[radman]

Just a quick update on the 8002 progress.  Your information was quite valuable.  To make a long  story short, I have seemingly appropriate voltage at all the checkpoints (R64 trimmer now maxed out) but still lack of complete function.  It appears to me (and that is a big “appears” that the problem is related to at least one (at the worm drive) and maybe a second (at the arm) photosensor.  Now waiting for parts.

Thank you for your help!

JM

[radman]

Success!  A new IR emitter at the wormdrive encoder set it right.  Now all functions seem to be working and it sounds great with just a used MMC3 cartridge.  Hope to upgrade that soon.

Sonavar’s advise was extremely valuable.  I doubt if I could have fixed this without his excellent posts.  For anyone attempting to repair one of these 8002’s (and particularly starting as a novice such as myself) check out his incredible online instructions… concise and with great pictures showing exactly where to place probes for testing.  I do have to add that after all the work with components open on the bench I thought I was never going to get everything crammed back into the cabinet!  JM

[sonavor]

That is great news.  I’m glad you got it back working again.  The Beogram 8002 is a great turntable to listen to.  I use mine all the time.

-sonavor

[chartz]

Hi,

That reminds me of my own Beogram adventures, some 12 odd years back! ?
Well done, with John’s invaluable help, but as we always said: pictures or it didn’t happen ?

A tradition here was to post plenty of restoration pictures, which was always really helpful.

Jacques

[radman]

The second of two Beogram 8002s is one the bench.  I do have a few pics to share later but these would be better if I could actually say something useful.  Right now, I have restored it from no standby light to about 90+% functionality but I am at another impasse.

The unit needed a new IR emitter at the wormdrive encoder (I replaced the two sensors also but had no actual data to suggest that was necessary).  LDR voltages are set at about 630 mV. I could not achieve satisfactory voltage at R72 on PCB1 so I tried replacing R64 with 10K and 20K trimpots.  This did not help.  Eventually, I tried replacing C19 with a 47mF/16V cap instead of the 1mF/63V cap originally on the board.  Initially, I thought this had helped as it did achieve higher voltage at R72 but was unstable and the tonearm still occasionally set down on the platter without a record.  I tested TR14, TR15 and TR16 but these were fine.  Finally, I completely removed R70 and went back to the original trimpot at R64 (4.7K  variable) and the original 1mF/63V cap at C19.  This combination seems to work best as the tonearm now sets down properly with a 45 or 33prm record and does not set down without a record.  However, there are still two remaining issues:

1. When not finding a record at the platter edge, the tonearm does not slow down but continues to scan across at initial speed.  However, if a 45 rpm size record is in place it DOES set down properly and plays through.  I am not sure this is a big deal but I believe it is designed to slow down.  The first of the two 8002s does this correctly.
2. At the end of a record the tonearm returns properly and the turntable motor shuts off but the platter is not induced to stop and continues to spin freely.  Again, not a terrible problem but I cannot figure out why it won’t.

So… if anyone has some ideas, I would love to hear them.  I am way past my knowledge base on this and probably made some mistakes in the above discussion.  Again, Sonavor has been very helpful, obviously having been through possibly every issue this turntable can toss out.

John M

[radman]

I forgot to mention that I reflowed at least 40 solder points on the PCB2 board and a few points under the platter but didn’t notice any changes.

JM

[Mark-sf]

The Lift Circuit (IC1/TR9 is supposed to trigger the brake (TR32) so I would start there. Since you have a second 8002 you have a unit to compare. As to the change in arm speed once it gets over the platter, I do not recall that it does this normally as there is no reason it needs to. I know it doesn’t slow down on the 4xxx Beograms.

[radman]

Thank you.  I’ll have another look at it for the brake.

Concerning the change in arm speed it sounds like I need to ignore that one.  The first 8002 I restored slows down for the search but you are correct, it doesn’t need to do that.

JM

[radman]

Finished!  Now knowing where to look (and finally examining the schematic) I found that the solder point at the base of  TR31 was elevated (see dental pick in image “pre”) with the corresponding trace to R109 obviously broken.  I placed a short bridge between the two points (Image “post”) and the brake function magically returned.

The turntable is now ready to be placed back in the case.  Thanks to everyone who have generously offered comments and suggestions.

John M

[thomash]

Hello:  Hope OK to ask for help with a 8000 someone gave me out of a shed.  I spent days getting new electrolytics in and reflowing solder joints on connector junctions and replacing the < > light bulb and rebuilding the lift plunger.  It worked for a few hours then I lost +15 and the platter now spins wildly fast nothing will stop it.  I even injected external +15 and regained some control over all the machine except platter speed which is like 100 rpm!  The tacho wheel lost some of its traces which I drew back on and the IC is reading some pulses but still speed is utterly unregulated.  Thank you for weighing in.

[Author]

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