I have just replaced the 2 big capacitors on the circuit board (2500uf 40v) with replacements with the closest value I could find which was 2700uf 40v. When I turned the unit on it ran for a second and then went dead. I have checked the fuse in the unit and it has burnt out. I was surprised as I thought that this higher capacitance would be OK. I have since put the old capacitors back in and am waiting for some new fuses to arrive. Am I correct in thinking that this capacitance blew the fuse or is something else going on? Thanks.
It's very unlikely that just using 2700uF instead of 2500uF caps would blow the fuses. If the caps had been fitted in reverse then its very possible. Another possibility is that the replacement caps had a lower internal impedance and this allowed a larger inrush current. I note the fuse is only rated at 100mA for 220v or 200mA for 115V, it might be worth getting 'slo-blo' fuses to reduce the risk of transient overload.
I personally would consider increasing the fuse capacity to 150mA for 220V supply, or 300mA for the US, still slo-blo; this increase would be sufficient to reduce spurious overloads at power-on, but still allow for the fuse to blow under fault conditions.
( I await a reprimand from the PC brigade for suggesting something that could be considered as reducing the safety of the device)
I personally would consider increasing the fuse capacity to 150mA for 220V supply, or 300mA for the US, still slo-blo; this increase would be sufficient to reduce spurious overloads at power-on, but still allow for the fuse to blow under fault conditions.
( I await a reprimand from the PC brigade for suggesting something that could be considered as reducing the safety of the device)
My guess is wrong polarization of caps. 2k7 is fine. I presume the capacitors were swollen or leaking. otherwise why else replace them.
I made sure the polarity was correct. On inspecting the fuse it was just a single broken wire, there was a M code on the outside of it. Don't know if this was a slow blow or not. I have ordered some new slow blow fuses online and will check if it works when I put one in.
M is medium blow. I dare say if the rectifiers are OK then a replacement fuse will fix it. M is also used in microwave ovens as they don't blow instantly. I think the service manual stipulates slow blow.
Thanks for your help. I will try the new fuse when it comes. In the meantime I have put the 2 big original capacitors back in. The reason I wanted to change them is because all of them are either bulging or leaking brown stuff. Will report back when the fuse goes in. Many thanks.
I've got a BOM for the Td-125 II which I used to rebuild my power supply and speed control. Several original components are no longer available, but the recommended substitutes worked fine. The info is on my office computer, if you still need it on Monday, let me know and I'll send it to you. In the meantime there is info on the analog-department web site.
Replaced the fuse and it works. Have now replaced 6 capacitors and set voltages. Not sure about DC voltage though. It's says to adjust to a minimum and no greater than 5mv. At the moment it is showing in minus figures, is this acceptable? Thanks.
Good to know you got it sorted. it doesn't matter whether the dc voltage across the motor is positive or negative, its the absolute value that needs to be as close to 0v as possible.
Do I need to keep checking DC every time I adjust the voltage for 33, 45 and 16? Or do I just do it once after checking 45rpm as it says in the manual? Thanks.
Just the once should be enough, just follow the instructions in the service manual.
It's a check to ensure the motor feed is balanced, which should help minimize any motor vibration.
It's a check to ensure the motor feed is balanced, which should help minimize any motor vibration.
When setting voltages I can never get the voltages that are stated in the manual dead on. For example, when setting 45 rpm I get 7.9, 8.0 and 8.1 but cannot seem to get the voltmeter to stay on 8 volts exactly. I have changed the 6 caps and cleaned the pots. Is there anything else to do here? Thanks.
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