Now for the final part of this Power Supply... The High Voltage Section.
This post only applies to the 520-5047-01 and 520-5047-02 boards. The 520-5047-00 board uses different parts, and will be covered later...Below is a pic of the High Voltage section:
As you can see, I've labelled all the different parts that are part of the High Voltage Section. If you have any problems with the HV supply, then it is best to replace the parts listed below, and not just the faulty part. Replacing just the faulty part will mean that this section will fail again reasonably soon as the other parts are already weakened. So, lets look at what needs to be replaced...
1) TR3, TR4 and TR6: These transistors are the output transistors for the 3 voltages needed for the Dot Matrix Display. They supply the +68Vdc, -98Vdc and -110Vdc voltages. Replace TR3 and TR6 with MJE15030 transistors, and TR4 with an MJE15031 transistor. Don't get these confused, as putting them in the wrong place will cause them to catch fire almost instantly at power on!
2) TR1 and TR2: These two transistors control the 3 output transistors. Replace TR1 with an MPSA92 transistor, and TR2 with and MPSA42 transistor.
3) Next on the list is the Zener Diodes. These diodes set the output voltages for the output transistors, and also set the bias voltage on the TR1 and TR2 transistors...
3a) D6 and D8 are the bias voltage zeners for TR1 and TR2. These are both 3.9 Volt Zener Diodes. Replace these with BZX85C3V9 or 1N5228 zeners.
3b) D9, D10 and D11 set the output voltages for TR3, TR4 and TR6. Replace D9 with BZV85C68, BZT03C68 or 1N4760B. Replace D10 with BZT03C100 or 1N4764. Replace D11 with BZX85C13 or 1N4743.
4) D5 and D7 are the half-wave AC rectifier diodes. These diodes rectify the AC voltage input into pulsating DC for the HV supply. This voltage is then smoothed by the C10 and C11 capacitors. Replace these diodes with 1N4007's.
The following list of parts are not essential to replace, but are a good idea to...
5) The C10 and C11 capacitors: These smooth the rectified DC voltage into a proper DC voltage. Without these caps, you would get "waves" through the display as the voltage fluctuates. Replace them with 220uF 200V electrolytic capacitors. (The schematic shows these caps as 150uF 200V, but the majority of DE power supplies have 220uF 200V caps fitted from manufacture)
6) The C12 and C13 capacitors: These capacitors decouple the voltage to ground. Replace these with 0.1uF 500V MKT or ceramic capacitors.
After replacing all of these parts, the High Voltage section should now work, and you will have your display up and running again!
