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
Very great read!
And reminded me of some trees I climbed looking for root causes on these damned lovable decks!
Sonavor: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.
I got present to that problem when C28 inside the processor "can" didn't ground. Boy! Did that lead to a wild goose chase and much frustration!
Lol the same thing happened to me when I read it.
He would not be denied by the 8002.
pfcs49: 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
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
Hi Phil, I am just a simple caveman living in a small town in Texas. I am afraid I don't have any Yamaha turntables although I have a lot of Yamaha speakers, preamps and power amps (quite fond of them).
pfcs49: 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"
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"
Do you mean the service manual?
-sonavor
sonavor: I am just a simple caveman living in a small town in Texas
As you see in Johns avatar, he even has long hair and beard, uncombed. NOT so, he is a truly Beoworlder, helpful, friendly and very knowledgeable in all what he does, his threads interesting and something to learn from.
Collecting Vintage B&O is not a hobby, its a lifestyle.
I have a broken beogram 8002. The "motherboard has a broken corner, and the push-keys unit does not function. everything else should be fine.
All parts are available, except the platter. (made a clock)
Cosmetically it is very nice. Happy to give away parts for any repair project.
"You think we can slap some oak on this thing?"
Keep that parts machine handy. I might need some getting my third 8002 working. Not in big hurry though.
"Do you mean the service manual?"
Yes-the service manual with higher resolution, please.
Well, I,m not a caveman-just a 67yo VW mechanic in a wheelchair. Nice to find someone else who can actually repair things. We are a vanishing breed!
pfcs49: Yes-the service manual with higher resolution, please.
You must be referring to the schematic diagram with color highlighting on page 4 of this thread. That isn't from a service manual PDF that is available. As mentioned in the page 4 posting, I created that drawing myself from a scan of the original page (from a hard-copy of the service manual). Then I used Photoshop to add the color highlighting to help me trace that particular part. The only PDF versions of the manual I have are from VE and the service manual section of Beoworld (requires Silver level membership). The VE PDF version of the manual has the full schematic as one image in the PDF while the other PDF scan has the schematic broken into multiple images. Neither of those PDF versions are super high quality. I just scanned that one part so I could show the problem I was trying to solve. Most of the time I work from the hard-copy service manuals.
Not too long after putting my Beogram 8002 back in service (the turntable that started this thread), its display started going on the blink. It doesn't affect the turntable performance so I have lived with it for a while as I didn't feel like re-opening this unit.Lately, I have been working on some Beogram 4002 turntables so I have been in turntable repair mode. I decided it was time to go in a fix this Beogram 8002 display.Here is a picture of the problem. You can see that 45 RPM displays okay but standby and 33 RPM have problems.
The second Beogram 8002 I worked on in this thread had an issue with the display that needed a re-solder of the 4.7nF capacitors that are part of the display circuit. My first step was to go through that exercise.This picture shows the components that relate to the display circuit. There are some resistors, capacitors, a few transistors and a display decoder IC (74247).
Re-soldering those display components did not fix the problem so the next step was to pull the components and measure them. I suspected the capacitors and maybe the transistors but I needed to remove most of the components anyway because space is very tight. I was glad I had added a socket for the IC as that made it easy to get out of the way.
These are the components I removed to check. Some of the 4.7nF capacitors were way out of tolerance.
I replaced all of the 4.7nF capacitors when I re-installed the components.
John did you get my PM about pegs
That did the trick. The display is working properly again.
Hi Søren,Yes...I thought I had replied but when I checked the conversation I can see I didn't so I just now sent you a response.Thanks!
Last year I acquired a couple more Beogram 8002 turntables as part of systems (one in a Beosystem 8000, the other with a Beomaster 6000). Both turntables were in excellent physical condition. One had power and appears to work okay, the other will not power up. While I am in Beogram repair mode I decided to look at both of these units last week. On the unit that would not power up, I went through the circuit boards and performed the re-flow of the solder joints as I recapped the boards. There were still problems with the power so I swapped out the transformer and the Beogram came to life. The turntable was not working correctly though. It had problems with its control logic. Play would start the turntable up and speeds would switch. however, the Stop function had problems and I experienced the turntable spinning in the wrong direction. I had one spare CPU left for this series of turntable so I decided to try it. That appears to have been the problem. The BG8002 appears to be functioning with correct logic now. I still need to go through and check the service manual adjustment procedures but I think this unit is almost ready for action again. On the second turntable, I need to decide if I will just do a thorough cleaning and lubrication, or if I will also do a recap. If this were a Beogram 4002 I would definitely do a recap. The circuit boards on the 8002 are so small and touchy that it is tempting to put off working them. I do plan to get rid of these two units though so having them both recapped would be good piece of mind.Here is a picture of the circuit board of the one I just got working.
That leaves me with no more spare processors for the Beogram 8002.Here are two of my bad processors. The top one is out of a Beogram 8002 unit I got for parts last year. The processor doesn't look standard. It may have been someone's attempt at a substitute. It doesn't work at all. The bottom one is the one that came out of this latest Beogram 8002. The spare I had on hand appears to be the same kind and appears to work.
Here is a picture of the replaced processor in the Beogram 8002. The numbers on it match the one I took out so I think I am good on this one.
In working on several of these Beogram 800x series now, I have found a very useful tool. Any idea why this tool works well on a Beogram 8002 (or 8000) ?
That Rockwell chip (Rockwell is no longer in that business anyway) looks very much like a programmable EPROM.
So, if someone was able to read the data out of a good chip, it would be possible to source another non-original chip, but with the same specs, and program that new chip.
I will talk to some IC-gurus in the US, and see if any of them can shed some light on that.
hamacbleu:To catch back the three suspension metal hooks when they fall at the bottom of the deck?
Very close. I got tired of managing needle-nose pliers on the tips of those wire loops (metal hooks) as I depress the leaf springs when opening up the Beogram and when finishing up. With the little hook tool I can easily grab the wire loop and hold it up as I maneuver the leaf spring off (or on).
This is a better picture to show how it makes managing the chassis suspension easier.
I just have the final stages of restoration left on this one. I let some orange GooGone gel soak into the old double-sided tape residue overnight. Then it scrapes off easily. I do that on all of the pieces that have the tape residue.
Menahem Yachad: That Rockwell chip (Rockwell is no longer in that business anyway) looks very much like a programmable EPROM. So, if someone was able to read the data out of a good chip, it would be possible to source another non-original chip, but with the same specs, and program that new chip. I will talk to some IC-gurus in the US, and see if any of them can shed some light on that.
I have never seen a 40-pin EPROM, and these are definitely microcontrollers. Mostek 3870 is a one-chip implementation of Rockwell F8.
Both of these chips clearly have a B&O part number stamped on them from the semiconductor plant (top 8340285, bottom 8340454) so any of us locals can leaf through the service manuals to try and find the product they belong into. I can confirm 8340454 is listed in the Beogram 8002 service manual. The other could be just a different software revision or from some completely different product, installed by someone who doesn't understand that the chip contains the product specific firmware as well.
Anyway, even if you could read the code out, it's not going to be of much use. The program code is in ROM and fixed at the time of chip manufacture. That's why the B&O part number is stamped on them already at the semiconductor plant. Therefore you won't find a blank chip to reprogram. Or, good luck finding one of the development chips with a socket for a piggypacked EPROM, at their time horribly expensive:
--mika
Mika is right; This is correctly a CPU with a built-in ROM. It has been produced for B&O as a custom chip, you cannot read out the code of its ROM.
BTW 8340285 is a Beomaster 6000 processor. It was produced the same way but obviously won't work in a Beogram. Good chance itwon't work in a Beomaster 6000 either now.
If you want to replace it with something modern, you will have to go through the same paces as Tim did with the Beomaster 8000 twin CPU.
Martin
John, I am very gratefull you are taking the time to photograph and detail how you are doing even the small things like removing glue and using your hook tool. For the experienced out there this may be familiar territory but to us with less experience this is both interesting and helpful. Thanks!
John
After the GooGone has set in for a while (I left mine over night), a plastic scraper and some paper towels can remove most of the old glue residue. What is left after that can be cleaned off with some ammonia and towels (plus sometimes, just bare thumbs).
This is the completely cleaned up BG8002 tonearm bay lid. Ready for re-attachment to the hinge.
Here is the cleaned up deck
Here are the cleaned up deck panels.
I will have to reinstall the panels tomorrow or the next day.To wrap up this BG8002 I performed the set down position check (SO Switch, the Manual << and > >> adjustment and a speed check.The Manual << and > >> adjustment is on page 5-3 of the service manual. I performed it on my second BG8002 in this thread back on page 16. It is worth showing again as it is probably over-looked.You put your negative DVM probe on P5-3, then measure with your positive probe on P5-4 while turning adjustment screw "A". You measure P5-6 when adjusting screw "B". In both cases you try to adjust for a voltage of 620mVDC after the Beogram has been running for at least five minutes.Here is my P5-4 to P5-3 adjustment -
Here is the speed check (using the same homemade test disk as on my BG400x projects...with my digital tachometer). The 33.33 RPM and 45.00 RPM speeds were good as you would expect with this turntable.
While doing the Manual << and > >> adjustment I noticed that I forgot the lock down screw for the BG8002 processor box (that secures it to the main PCB. So I opened up the Beogram one more time and secured it.Another thing to note about this Beogram 8002 and the one before it (in this thread), this circuit board doesn't have the additional resistor across the tonearm drive motor. Was that resistor added as a service modification later by B&O ? The resistor on the previous BG8002 in this thread can be seen on page 13.
Not many Beograms are exactly like the one shown here.There are countless versions and there were lots of minor revisions and production changes.As you have also noted, even your own two decks are not identical.
Nice thread and great photos!Remember to do all work in an antistatic environment. The processor in particular, is a sensitive little thing andthere are far from plenty of them around.
Dillen: Remember to do all work in an antistatic environment. The processor in particular, is a sensitive little thing andthere are far from plenty of them around. Martin
Remember to do all work in an antistatic environment. The processor in particular, is a sensitive little thing andthere are far from plenty of them around.
This thread has a similar picture to this but for completeness of this latest BG8002 project I figured I would include this photo. It shows the preparation for re-attaching the Beogram deck panels and shows the static discharge spring in place (must be in place prior to attaching the panel).
Here is the latest BG8002 project completed and in my test room. I attached an MMC2 cartridge and put on some Stevie Ray Vaughan. The Beogram sounds wonderful of course. Now just one more of these 8002 units to go, then I can start on the BG4000 project. I am anxious to start the other project but will be patient and careful with the last 8002 Beogram. One thing I hope this thread has shown is that these decks are really fantastic machines but they are also very delicate. You have to go slowly and check everything carefully.