Beogram 1700 speed trouble

[kenkirk]

Hello,

I just recapped my Beogram 1700 with the kit from Beoparts. No schematic. The caps they sent me were confusing on polarity. I thought I had it right, but I reversed 2 caps and it blew the fuse. I researched the Cosonic caps and was able to properly determine the polarity. I replaced the 2 reversed caps properly and replaced the fuse. The motor runs, but at a very high rate of speed. When pushing turn, it ramps up fast, 33 way fast, 45 very fast. I did replace the trimmers, but this is no where near the correct speed. Anyone have any ideas of what could have gotten blown? Where to check?

 

Thanks!  Ken

 

 

[Mark-sf]

If you have access to an oscilloscope you should find a 500Hz sine wave on P1 of the motor connector when the speed is set to 33. It’s possible that the motor control chip has been damaged. Check the schematic available at https://beomanuals.com/manuals/Beogram/Beogram%202402/Beogram_2402-Schematics.pdf. While its a different model it uses the same motor control circuit.

[kenkirk]

Yes I have a scope. Thanks! I’ll check it.

[kenkirk]

Ok, some progress. 33 is rock stable. 45 hunts and pecks and is not working. But worse, a loud servo noise is coming over the phono plugs. Not a little, but so loud you cant listen to the table. This table has always been dead quiet. The isolation washers under the PCB and TO-220 are in place. Any ideas??

[Mark-sf]

I don’t know what you mean by “servo noise”. If you mean 120hz buzz then it’s likely a power supply cap problem. As for the 45 sod are you seeing a variable freq on pin 1?

[kenkirk]

It was like the noise of a iPhone getting too close to a AM receiver. Anyway I found a cracked solder joint on a cap and its possible I left a cap lead too long and it touched the base. Anyway I will never know for sure. I trimmed the leads and reflowed the solder and the noise is gone. Table sounds great at 33. The 45 trimmer will not get to 22k, it stops at 17.5k. That is probably why it will not lock onto 45. Anyway I am gifting this old trusty table to my son and he does not intend to play 45’s. If later he does, I will source another trimmer .Thanks for your suggestions. I never put a scope on P1. I was looking for obvious troubles and it was the cracked pad and possibly a lead touching the base. I bought this table in the 80’s. It is bringing back fond memories. I hope my son has fun with it now!

 

Ken

[Mark-sf]

Hope your son appreciates it!

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