Boegram 4000 tonearm problem

[sweatybetty]

Hello all, new member here.

I was brought a BG4000 for repairs that was in about 40 pieces. At this point I have everything working as it should except for 1 issue.

The tonearm will not lower either with or without a record on the platter. If I push any of the buttons on the control and stop the tonearm, then push any button again, the unit will work as it should. If I turn the variable resistor on board 1 fully opposite, the tonearm will lower with or without a record on the platter. There is no happy in between.

All switches have been cleaned and measure around 0.1-0.2 ohms.

All power supply caps are new as well as 1C9 and 1C14

Hooking up a scope at 1TR14-1TR17 show signals nothing like shown in the manual.

I can also change the 6V output at 1TR19 by blocking the photocell in the tonearm.

I have been all over Beolovers site but havent found anything that helps.

Im going to try attaching some pictures of the scope signals.

The first is at the base of 1TR14 and the collector of 1TR17, (same signal) the second at the collector of 1TR14

Thank you in advance!

 

[hcraig244]

Is the platter spinning with the tone arm over the rotating ribs in the scope readings?…..looks like it is….so the photovoltaic cell looks like its still working, good news.

Are you sure the readings are taken at the points you identify above? and as the tone arm will drop under some conditions then the solenoid and associated linkages/damper pot etc are all working, more good news.

I think the potentiometer  you refer is the one installed to enable playing transparent disks? does the tone arm stop at the correct place when a disk is played….or just run to the left side then run back to the rest point?

Craig

[sweatybetty]

Craig

Yes the tonearm is over the spinning platter.

I soldered jumper wires to the points shown on the schematic in order to get the scope readings

Yes the pot is the one for transparent discs. The arm will drop in the correct spot with or without a disc on the platter with the pot at one end of travel. If I turn the pot the other way, the arm will not drop at all, but will run to center then back to stop.

Going through the flow chart, I get to step 4 ok but am having some trouble understanding the points to check as everything is abbreviated.

Thanks again

[hcraig244]

The main forum product section contains manuals for the BG4000 and also some training notes donated by a member who was a one time repair engineer who went on a training course and reatained the course notes…..these notes identify the abbreviations and are a very usefull guide…..they are available to silver members and above, take a look…..do you have a transistor tester available?…….seems like your machine is only a short way from being sorted…..

[hcraig244]

“The first is at the base of 1TR14 and the collector of 1TR17”

Looking at the schematic I dont see a point showing a scope reading at the collector of 1TR17 ?

[sweatybetty]

Craig,

Im only a bronze member at the moment so I cant view the info you mention. I dont work on much B&O stuff and haven’t had enough trouble in the past to post for help.

I do have a tester and some BC547 transistors that are coming up as a close match. May just replace them one at a time and test as I go. The only one Im missing is TR18.

As far as testing TR17, that is a typo on my end

Need to step away for a couple days while I still have some hair!

Again, thank you

 

[sweatybetty]

Found it! 1TR15. Replaced it and everything works fine. Waveforms are still wonky though. ???

Going to replace the rest of the transistors and also the caps tomorrow, do some final adjustments and send it home.

Thanks again

 

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