Hi
I am new to this forum. A friend of mine brought this reel to reel to get it fixed. The problem was, the fuses keep blowing. When I first ON the tape player there was no lights on any indicator and the VU meter was dead. Upon opening, I realise that 3 fuses, the +15V, -15V and +50V have blown. I replaced them and turned ON the player again. I realised that both the VU meters have swinged to the maximum (fully clockwise) and the +6db,+9db and +12db red indicators are on, no output and the tape deck 'STOP" indicator flashing. I OFF and ON back the player and the same results. When I OFF and ON the third time , the fuses blown again. Can someone assist by advising me what could have gone wrong or where should I start troubleshooting.
Thanks
Carlos
Carlos
Unfortunately, it isn't as easy to pin point the cause of the fuse blows. I would not replace anymore fuses and power up the sick machine again until you have located the sources of the problems. The +/- 15V fuses and +50V fuses are blowing more than like due to faulty electrolytic capacitors downstream from the fuses. I would suggest you track down the problem one step at a time.
+/- 15V are for audio section and more critically +50V is for your Spooling Motor Control and Capstan control boards. I would suggest you focus on +50V problem first. There are two major area of known problems with these machines. if you have a A807 Mk I, it is more likely you will have problem with the stud mount can type electrolytic capacitors C1 through C4. C1 charging capacitor is for +50V. By unsoldering either the black or red wires on the cap terminal, you can test the health of the cap with a capacitor meter. Or just replace all four of them. They are the dreaded Frako made and will eventually fail. Once you have done the C1 repair/replacement, you can move on to the other areas of problems.
Both the Spooling Motor control board and the Capstan Control board are known to have the smaller Frako capacitors, C23, C24 in Spooling Motor control and C65 in Capstan Control boards fail all of them at 220uF 63V. If your A807 is not MkII and if the axial capacitors in the Spooling Motor Filter board - that is attached to the Spooling Motor Control Board - are not blue Phillips type, I would replace them while you have the board assembly out. they are 6 ea 100uF and 6 ea. 47 uF at 60V axial electrolytic capacitors.
After you have made the repair on both Spooling Motor Control Board and Capstan Control board, you can disconnect the red and black wires (after marking their position) from both boards and then replace the T4A fuse for +50V supply. You can now power up and if the C1 is good, the T4A fuse will not blow and you should be able measure +50V between black (-) and red (+) supply for Spooling Motor Control. If you get +50V, then power the machine off, reconnect the red and black wire on just the Spooling control board (leave the red and black wires on Capstan board unconnected for now). If the C23, C24 and Spooling MTR filer caps are all good, Spooling Motor Control board should work well.
Next you can measure the red and black wires on Capstan board and you should get -50VDC. If the C65 is replaced, Capstan should be working. You can reconnect the supply voltage wires with machine off. You can turn the power on, manually move up the tension roller by hand, and hit Play. Both spooling motors should spin as well as the Capstan will turn.
there are other possibilities of one of the semiconductor such as diodes or transistors going bad but it's rare.
It's a same process of troubleshooting for Audio section to repair for the +/-15V supplies. Hope it helps. Ki