PDP-11/04 - Power Supply Part 3

With the power control, main transformer and fan assembly operational the next module in the power supply is the 15VDC regulator.  This mounts on the other side of the power control box and is powered from the 28VAC output of the main transformer.

15VDC Power Supply

As well as 15VDC, the module also provides AC and DC Low signals and a 50hz signal for the real time clock on the DL-11W serial board.

There are two electrolytic capacitors on the board that needed testing before I was willing to connect it to the main transformer.

I built the capacitor test jig described by on http://dustyoldcomputers.com/pdp12/pdp12/restore1.html using junkbox parts.  

Capacitor Test Jig

Combined with 3 batteries saved from the UPS at work I was able to test and both capacitors on the 15VDC regulator board and they seem to be serviceable.

Capacitor Test Jig

 

PDP-11/04 - Power Supply Part 2

The next module to be tested is the main transformer/fan assembly.  This takes the switched 240VAC output from the control box.  The fans run at 120VAC and the main transformer provides a number of 28VAC taps which power the various regulator modules.

Variac

Once again the VARIAC was a great help.  The end result seems fine..... no smoke, everything running well, 28VAC out at 230VAC in.  

Variac

Variac

Boy those fans make some noise although probably not significantly worse than the servers at work.  Overall the transformer seems in pretty good physical condition... you can see in one of the photos that there is some rust on the transformer frame but otherwise nothing major.  

Variac

One of the fans is a bit noisy because the blades scrape on the inside edge... I think that has happened is the paint has started flaking.  Doesn't seem to cause any major problems though.

Next step is the 15VDC regulator module.  Unlike the others which are removable modules this is mounted on the other side of the control box.  

As well as 15VDC it provides power monitoring signals AC LO, DC LO and a timing signal derived from the mains frequency and used to drive the real time clock board.

The 15VDC board is the first with big electrolytic caps (one really big one on the regulator output).  I am going to try the 5ma @ 40VDC approach using some gel cells in series and a resistor and see how that goes.  As much to record the change in voltage over time across the cap for my own interest.  

Once I know the state of the capacitor then I will use the variac again to bring the power up slowly and see how the regulator reacts.

 

PDP-11/04 - Power Supply

I borrowed a Variac from a mate and what a great piece of test equipment.  Not something you need everyday but when you do it it worth it's weight in gold (that is probably quite a lot because it is pretty heavy).

Variac

Made a start on the PDP-11 by testing the Power Control box.  

This is where the 240v comes into the power supply and it has a "lower" voltage circuit that goes to the front panel power switch.  

It has a small transformer, capacitor and a power switching relay.  

Powered it up slowly to 240v using the variac and all seems good.  There are multiple 3 pin sockets on the unit any of which can switch the main 240VAC power on and off and they test out OK.

Variac

The switching relay requires at least 150VAC to switch on which is interesting.  They certainly didn't go for low power parts here.

After the relay the switched 240VAC comes put on a 4 pin connector that looks just like a power connector on a 5.25" floppy drive.  Quite petite after the massive power cord that goes into the power control unit.

The next test is to connect the main power supply frame to the 4 pin connector on the power control output and test that out.  The frame has the main power transformer and the two cooling fans.  The output from the transformer should be 30VAC and the fans run from 120VAC.  

The nice thing about the switching relay in the power control box is that you can put a small insulated weight on top to push the contacts together and switch it on.  This means I can have it on from 0VAC rather than waiting until the variac output reaches 150VAC to switch and then find there is a problem with the transformer or fans and smoke comes out.

 

PDP-11/04 - New Project

Sometimes the unexpected happens.... I got an email from a retrocomputing enthusiest who was leaving the country for a couple of years and wanted to know if I wanted to look after his PDP-11.  

Of course there is only one answer to that!

PDP11/1

 

eBay AD9850 Module Test Board

Test board for the cheap eBay DDS modules. The board is based on a design by WB2V with software enhancements by AA0ED and AA0ZZ.

The cheap AD9850 DDS modules currently available on eBay are a great starting point for a signal generator project but are a little short on documentation.

The pinout and relationship to AD9850 pins is as follows:

 

Board Board AD9850 AD9850
Pin Label Label Pin
       
1 VCC DVDD,AVDD 6,11,18,23
2 CLK W_CLK 7
3 FQ FQ_UD 8
4 DATA D7 25
5 RST RESET 22
6 GND DGND,AGND 5,10,19,24
7 QP QOUTB 13
8 QN QOUT 14
9 SINA IOUTB 20
10 SINB IOUT 21
11 GND DGND,AGND 5,10,19,24
12 D7 D7 25
13 D6 D6 26
14 D5 D5 27
15 D4 D4 28
16 D3 D3 1
17 D2 D2 2
18 D1 D1 3
19 D0 DO 4
20 VCC DVDD,AVDD 6,11,18,23

All required pins are available to for the WB2V reference design (http://www.qsl.net/yo5ofh/projects/dds_vfo_by_n2apb/dds_vfo.htm) to be implemented.

Use the updated siggen3a source by AA0ED and AA0ZZ available from
http://www.njqrp.org/ham-pic/projects.htm and update as follows for the 125mhz reference oscillator:
 

;==== Currently set for 125 MHz Oscillator =======
ref_osc_3 equ 0x22 ; Most significant osc byte
ref_osc_2 equ 0x5C ; Next byte
ref_osc_1 equ 0x17 ; Next byte
ref_osc_0 equ 0xD0 ; Least significant byte

 

"Not so secret...."

"Not so secret".... Communications room - USS Intrepid - September 2011.

 

"Spare Parts"

"Spare Parts".... ex NZ Government Railways DJ 3021 stored at Middlemarch for the Taieri Gorge Railway - March 2011.

 

eBay AD9850 Module Pinout

The cheap AD9850 DDS modules currently available on eBay are a great starting point for a signal generator project but are a little short on documentation.

The pinout and relationship to AD9850 pins is as follows:

 

Board Board AD9850 AD9850
Pin Label Label Pin
       
1 VCC DVDD,AVDD 6,11,18,23
2 CLK W_CLK 7
3 FQ FQ_UD 8
4 DATA D7 25
5 RST RESET 22
6 GND DGND,AGND 5,10,19,24
7 QP QOUTB 13
8 QN QOUT 14
9 SINA IOUTB 20
10 SINB IOUT 21
11 GND DGND,AGND 5,10,19,24
12 D7 D7 25
13 D6 D6 26
14 D5 D5 27
15 D4 D4 28
16 D3 D3 1
17 D2 D2 2
18 D1 D1 3
19 D0 DO 4
20 VCC DVDD,AVDD 6,11,18,23

All required pins are available to for the WB2V reference design (http://www.qsl.net/yo5ofh/projects/dds_vfo_by_n2apb/dds_vfo.htm) to be implemented.

Use the updated siggen3a source by AA0ED and AA0ZZ available from
http://www.njqrp.org/ham-pic/projects.htm and update as follows for the 125mhz reference oscillator:
 

;==== Currently set for 125 MHz Oscillator =======
ref_osc_3 equ 0x22 ; Most significant osc byte
ref_osc_2 equ 0x5C ; Next byte
ref_osc_1 equ 0x17 ; Next byte
ref_osc_0 equ 0xD0 ; Least significant byte

 

FT736 and Ham Radio Deluxe

KA6BFB/N6BIL FT-736R HRD interface (http://home.comcast.net/~tinkyr/736/N6BIL%20Hardware%20Emulator.htm) assembled from through hole parts. Emulates an FT-847 so Ham Radio Deluxe can control the RX and TX frequencies during satellite passes.

A whole new life for the FT-736.

 

Codan N3ZI DDS

Another project in progress.... installing an N3ZI DDS2 into a Codan 6801 Marine transceiver.

The N3ZI works well as a crystal replacement and requires no buffer amplifier in the Codan 6801.

More work to be done automatically switching the DDS2 channel, IF offset and USB/LSB settings when the front panel channel selector switch is changed and a bit more cleanup on the panel.

Inspiration and the Codan for this project from Murray Greenman ZL1BPU (http://www.qsl.net/zl1bpu/PROJ/Recycle1.htm)

 

SI570 QRSS Beacon

My MEPT QRSS and WSPR beacon is controlled by a DLink DSL-502T running OpenWRT.

The QRSS and WSPR messages are generated by directly controlling the frequency of an Si570 chip.  The interface to the Si570 is I2C.  The DSL-502T can provide an I2C interface using the J5 GPIO interface connector and the I2C gpio bit bashing drivers.

The output from the Si570 is amplified to an N7KSB style amplifier based on an 74HC240.  This is run at 8v and provides approximately 120mw power output into a 50 ohm load.

Filtering of the amplified signal is by the "Kits and Parts" 30m bandpass filter.

The QRSS beacon with a QRP random wire tuner loaded by Murray ZL1BPU.

Internals showing the DLink DSL-502T (foreground), Si570 (top right), Amplifier (top centre) and Filter (top left).

Closeup of the Si570, Amplifier and Band Pass Filter.

Schematic.

 


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Contact Andrew Quinn

jaquinn@ihug.co.nz http://twitter.com/jaquinn