The Soul of an Old Machine

My Nova 3’s 128kW Plessey Memory Board has another bit error – bit 7

Tommie — Sun, 25 Apr 2010 17:37:40 +0000

The Nova’s memory error indicates a flaky signal, but which signal? The error manifests itself on address 40000(oct), bit 7, but only running MEMDIAGLONG.ASM. Running MEMDIAGSHORT.ASM and MEMADDRTEST.ASM on the full 32kW works fine. MEMDIAGLONG runs fine up to the 16k boundary which would imply a faulty memory chip with a pattern sensitive problem, but manually loading memory generates a parity error in any location for bit 7, including the first 16k, which would indicate a faulty bus latch.

(MEMDIAGSHORT.ASM, MEMADDRTEST.ASM and MEMDIAGLONG.ASM are diagnostics by of 11/27/79 by T.P. Povlick that are loaded using the front panel switches.)

Nova 3 Plessey 128kW Memory Board with IC U146 16kx1 memory MK4116N-4 removed

The bit 7, address 40000 – 77777 (oct) error is now fixed by replacing the chip at row 2, column 7; IC U146. The 16kx1 memory IC is a MK4116N-4. (The Plessey board is 128kW consisting of 8 rows and 16 columns of 16kx1 chips.) Running MEMDIAGLONG.ASM on the full 32k now works fine. Since I currently have no floppy, disk or tape drive attached to the CPU, I am unable to run diagnostics on the full 128kW (256kB) address range.

I started the memory testing program MEMDIAGLONG at 13:50. The program runs 10 minutes per 1k of memory and was finished at 19:10 with no errors. Time running = 5h20m.

The 256kB Plessey Memory Board has a bit error

Tommie — Wed, 10 Mar 2010 14:47:36 +0000

128kb Plessey DG Nova 3 Memory Board

Bit 9 cannot be set after the machine has been running for 5 minutes or more. Clearly a thermal problem. Without the board schematics I will have to trace the MEM9 signal from the card edge connector inwards. Schematics would have been great! If you have the schematics for this board, a copy would be much appreciated.

The bit 9 error is now fixed; it was a faulty SN74S373 latch on the memory bus.

The Nova 3/12 Console is repaired

Tommie — Wed, 24 Feb 2010 15:02:18 +0000

The ”Stop/Reset” toggle switch wouldn’t toggle back to its center position so I took a switch from my other Nova 3 console. Turns out that this switch would not make contact in the “Stop” position and I had to grab yet another switch from my other front panel. Looks as this front panel rapidly is becoming an assembly to salvage parts from.

All indicator lights are now replaced. The leads of the ones that did work where extremely brittle and since incandescent lamps have limited lifetime I decided to replace all lamps. Lights 7 – 12 would not lit or if they did, they lit very dimly and sporadic. The driver chip, DG part # 113-7748 was faulty and I replaced it with a NTE74LS06 chip (Hex Inverter Buffers/Drivers With Open-Collector High-Voltage Outputs).

Now that the console is working (apart from lacking the XX2065 key which I have ordered), I can start testing the cpu and memory.

Nova 3 Console disassembled

Nova 3 Console Lamp Driver DG part 113-7748

Nova 3 Console Lights works fine after replacing all lamps and a driver IC

Powered up my Nova 3/12 today

Tommie — Sat, 13 Feb 2010 23:33:32 +0000

After sitting in my hallway for 3 months now, I finally got around to do some work on my Nova 3/12. The installed power supply was faulty. 5 VDC worked fine while all voltages based on the raw 15 VDC was missing. I did some trouble shooting but decided to use the power supply from my other Nova 3/12 chassis. This power supply worked fine after replacing the 5VDC and 15VDC capacitors on the Power Supply board and adjusting the 5VDC and the 15VDC voltage levels.

With only the front panel installed I applied power to the chassis and a plume of smoke rose from the front panel logic board and the typical smell of burnt electronics spread throughout my apartment. I quickly pulled the power plug and disassembled to front panel. One of the decoupling capacitors on the 15VDC power bus had its plastic coating melted and of the internals only a black crust remained. Not unusual for old capacitors to develop a short. I decided to use the front panel from my empty Nova 3/12 chassis and voila – the light bulbs that were not broken came on.

I’ve ordered 30 sets of 28V .04A Hudson 2187D equivalent lamp bulbs and a fan that needs replacing.

Data General Nova 3/12 Power Supply drawings

Tommie — Sun, 07 Feb 2010 15:13:13 +0000

I have two Nova 3/12’s. One equipped with:

NOVA 3 CPU, PWRFAIL, PRLOAD, 256KW
NOVA 3 TRIPPLE OPT, MMPU, PAR, MUL/DIV, RTC
64KW Plessey, 128K SC, W PAR, 0-127
DGC NOVA CASSETTE I/O, $TTI/O, 9600 B, RTC
DISK CARTRIDGE CONTROL DGC NOVA, DKP, 4234, 6030
DGC NOVA CASSETTE I/O, $TTI/O, 9600 B, RTC

The other is an empty chassis, both with faulty power supplies. I contacted Bruce Ray of Wild Hare Computer Systems and Bruce provided me with Nova 3/12 Power Supply and backplane drawings. I still have to troubleshoot and repair the power supplies, but at least I now have the drawings and the tools.

FMV to arrange shipping

Tommie — Mon, 01 Feb 2010 17:04:17 +0000

FMV is looking into the possibility of shipping the S/280, the disk drive (don’t know the type yet) and two DG 2265 CRT terminals to me using their internal military transportation system.

Just received some pictures of the S/280

Tommie — Thu, 28 Jan 2010 17:28:15 +0000

Today my contact at FMV sent some pictures of the S/280 and the disk he has in storage and that they will donate for free to me. The guy is extremely friendly and helpful and so is his boss. The world would be a much better place if people were like these guys and I owe them a big “thank you“! Will work out with FMV how to ship the equipment to me.

Brought the Nova 3 home to work on it

Tommie — Tue, 17 Nov 2009 17:23:10 +0000

I brought the Nova 3 home and put in on a workbench in the hallway with the intention of:

stripping it to pieces
clean the metal parts from dust and rust
clean the plastic front panel
clean the PCB’s from dust, dirt and oxide
check the power suplly for correct voltages and ripple
assemble the parts
test cpu and memory

Picked up a Nova 3/12 from my friend Bjarni

Tommie — Mon, 16 Nov 2009 17:21:55 +0000

A fellow Data General minicomputer collector offered me his Nova 3/12 a while back and today me and friend went to his place to pick up the Nova 3. Bjarni, as the friendly guy he is, also offered me to take his Model 4234, Diablo drive which I did. I now have a DG 19” rack, the Nova 3/12 CPU with:

NOVA 3 CPU, PWRFAIL, PRLOAD, 256KW
NOVA 3 TRIPPLE OPT, MMPU, PAR, MUL/DIV, RTC
64KW Plessey, 128K SC, W PAR, 0-127
DGC NOVA CASSETTE I/O, $TTI/O, 9600 B, RTC
DISK CARTRIDGE CONTROL DGC NOVA, DKP, 4234, 6030
DGC NOVA CASSETTE I/O, $TTI/O, 9600 B, RTC
A 4234 Diablo disk drive and a 6026 Vacuum Tape Transport

I believe the Diablo disk drive was part of the Nova 3/12 system since it has a disk controller installed for the Diablo drive.

Called FMV

Tommie — Wed, 11 Nov 2009 17:21:08 +0000

Asked about the status of the Eclipse S/230 and was told that the CPU will be replaced in 6 months from now at the earliest. (It still has my name on it should when it becomes available). My contact tells me that he’s been to their storage facility and found one Eclipse S/280 sitting on a pallet. Obviously I was interested in the S/280 and told him that if he had any 6045 disk drives that would be interesting as well. He will take another look at what they have and send me pictures.