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
Hi, I'm gradually repairing a Beogram 4002 (type 5524, DC motor). Everything now works as far as I can tell until the arm solenoid engages, then one of the two power fuses blows. Does anyone know where I should check for the cause? Thanks Richard
One possible problem might be the microswitch operated by the solenoid mechanism. When the solenoid first pulls, it receives a much larger initial current. Then the switch opens, and the solenoid receives its current through a dropper resistor that reduces the current to a "hold" level. If the switch doesn't operate, the solenoid overheats, the wire insulation might melt and it short circuits. Then it might blow the fuse.
Disconnect one end of the solenoid and measure its DC resistance. I seem to recall it should be around 8 ohms, if it's close to zero it has shorted. The solenoid can be rewound if you're patient enough - there's a thread on that somewhere in the forums, was it Graham's BG6000?
You will need to repair the switch problem as well. In old models, the lever that operates it is plastic and it might have cracked. Another possible problem is that the switch has lost the plastic part the lever is supposed to push on. You might find it loose inside the deck somewhere...
EDIT: found the old thread, it was in the archives:
http://archivedarchivedforum2.beoworld.org/forums/t/34064.aspx
--mika
Hi, thanks for your reply. My deck might be a slightly different version, as it doesn't have the microswitch near the solenoid. If I replace the fuse everything works again until the arm is lowered. The solenoid operates for perhaps a second, then the fuse blows again. I'm tending to think it might be the Darlington transistor IC4 and the two associated transistors ( TR 9 & TR 10) in the magnet coil circuit. I hadn't thought of checking the solenoid coil, but will do so now.Thanks Richard
As far as I remember, there is a cap in that circuit too, so check TRs, cap and coil
Collecting Vintage B&O is not a hobby, its a lifestyle.
Hi, regarding the magnet coil circuit, I've changed TR9, TR10 and IC4 transistors, all the tantalum capacitors, and checked the solenoid coil (measures 8 or 9 Ohms). The problem is just the same. Everything appears to work, except that when the solenoid activates a power supply fuse blows after a few seconds. The only parts unchanged in the circuit are 4 resistors. Have you any ideas on what I should check next? Thanks Richard
Further to my last post, I've checked the current going to the solenoid coil. It measures 140 mA approx., which is in spec. What other circuits begin to operate after the arm drops which could cause the fuse to blow? All the best Richard
Have you confirmed that the fuse rating is correct ?Has the deck been converted to a different mains voltage ? Some versions require achange of fuse rating if mains voltage is changed.
Martin
Hi, the mains voltage is 240 v, and the two fuses are T250 mA slow blow. If the arm isn't dropped on the record the fuses don't blow. When a fuse does blow there is no smell of overheating etc, and when replaced everything is as before. All the best Richard
Found the cause of fuses blowing to be a defective mains transformer. On running the turntable from an outboard 24 v ac supply, everything is fine. Thanks for help given, all the best Richard