This is a Very Dead Vectrex Repair and yes I am praying in the reflection that I can save it 😉
When I got this home I had a look inside and quickly closed it up as it was not a pretty sight. It broke me out in a sweat it was that bad so I decided to tackle it another day……
Three years passed…
I heard from a friend that Elite is available for the Vectrex and thought, Its time….
I gave it a casual clean and opened it up. Then looked for any capacitor leakage or scorch marks from failed components but all “seemed” ok.
So I powered it on and…..
Nada, no sound no display nothing. But wait, I’ve just noticed on this image from a few days back. It looks like there is a dot on screen or is it my watch reflection? I didn’t notice anything at the time. I checked the fuse beneath the Warning label in the image below, it was fine.
So what about the dot?
I’m not even sure if it was plugged in at that point as I can’t see a power cable leading off the table to the right, which is where my mains sockets are located. Oh well I’ll cary on my assessment regardless.
There definately is a power switch issue as only half the wires are showing continuity when switch on. As seen below the power switch provides continuity from red to brown. There are two pairs and only one of them is providing power.
When powered on there is power to the logic board as there is -5v (Yellow wire), +5v (Orange), -13v (Red) at the connector in the image below so some power is getting through.
There is no sound or buzzing when switched on and I don’t notice any dot or anything at all on screen. The tube at the back isn’t lighting up so the dot must have been either a micro ghost or a reflection.
Courtesy tube discharge. WARNING there is a serious risk of electric shock doing this unless you know what your doing. Pacemaker people, please don’t try this. I always wear rubber gloves when tube discharging and should actually only be using one hand to discharge as the shock can go across your chest otherwise. That being said, here I go.
Actually in this case if there is no glow from the neck of the tube so there is unlikely to be any charge in the tube and there wasn’t.
Checking power at the switch across the red to brown wires revealed only one board was getting power. I did short the pins across the non working part of the switch but there was no change as the screen remained blank, no sound and no activity at the neck of the tube.
Lets dissasemble and get to that switch.
A ground wire connecting the power board to the logic board needs to be desoldered and disconnected.
There are four screws around the transformer to remove
A screw next to the power switch
A couple of screws on the logic board
With the logic board removed the power switch must be desoldered and removed. This allows the metal tabs at the top to be pryed away from the black plastic top.
With the tabs opened the black plastic top simply lifts off but be careful as there is a sprung connector inside.
The sprung connector can easily be lifted out with the dog bone latch which fits into the contacts shown below.
Below is the sprung connector shown in the on position.
And here is the off position. This position is required to be set when refitting.
The contacts were quite gummed up and so were given a good clean with alcohol and contact cleaner. Additionally a bit of light sanding of the contact points.
Reassemble by setting the switch to off with the black plastic peg visible through the crescent slot.
The sprung connector set to off needs to be placed with the metal part inserted in to the hole and crescent slot. It is held in place by the spring which is off center so remember this as the black cap must be maneouvered so the near central peg is moved to the center.
Put the dog bone back on in the horizontal position.
Now the tricky bit. Orient the black cap to align with the metal tabs. As stated the grey connector is sprung off center and must be moved to the center as the cap is put on. Angle the black cap onto the central grey peg on the connector and slide the black cap into position. You will feel the sprung resistance moving the grey connector to the center. The cap should align with the tabs ready to clamp.
Before claimping the tabs back firmly hold the black cap on while turning the switch to on. Check that the switch clicks while doing so. You can also check continuity at this point but you must make sure to firmly hold the cap in place. Once verified continuity then move the clamps in place. If no click is heard then remove the cap and reseat the grey plastic connector and try again.
The switch is now repaired and as recommended its best to leave it on and just use the plug socket to switch the unit on and off. The transformer actually remains powered even when the the switch is in the off position so never a good idea to leave the power on at the plug with a Vectrex.
Broken wire
One of the wires came off while fixing the power switch so I decided to make a connector to easily disconnect and connect these wires
Removed the wires and cleaned up the holes
Need to strip the red wire back. Pin headers ready to be soldered in.
Connector finished
Need to make a red mark to signify which orientation the plug is connected.
checked transformer secondary voltages on power board EP104, EP105(Center white), EP106
First EP104(Brown wire) to center 10.7v
EP106 (brown wire) to center.
10.7v on both sides so transformer looks ok.
Withe the boards extracted I checked for a clock signal pin 34 on CPU
Looks good. I’m not sure the Vectrex is still very dead as this repair has sort of rendered it undead. Life signs remain faint.
Went through all the chips checking 5v and found the sound chip IC208 is showing only .2v on pin3.
I use this tool called openboardview which really makes this process so much easier and its FREE!. For any retro troubleshootists I fully recommend this if you can get a BRD file for whatever your troubleshootisting.
5v lines check ok except….
IC208 AY Sound chip .2v
Socketed and replaced from a doner Spectrum +2A. The AY sound chip now shows a healthy 5v on pin 3 but still no life from the Vectrex.
IC 202 SN74LS00 measures a slightly suspicious 4.7v. This can be indicative of a faulty chip. This is a logic chip of nand gates so I’m going to check the gate pins on the oscilloscope and look for any incorrect logic or poor signals. There was a similar symptom on the sound chip earlier.
The wiring is bit brittle. had to reconnect the audio wire. I was hoping this was the reason for no audio but no such luck.
I was going to pull IC202 but its voltage now measures 5v consistently.
IC203 Read Write Ram
I have connected to pin 32 of the CPU and get activity on boot which gives regular pulses sometimes, or stops and flat lines after a few sceonds or emits a very weak signal. Suspect.
Tracing this signal line leads to ram write enable via the IC203 74LS32 nand gate. The ram/read signal has no activity which is strange so I’m going to pull IC203 and socket /replace if necessary.
I discovered the old Sinclair ZX81 has the same ram so decided to harvest until replacements arrive.
Pulled, socketed and replaced ram in the Vectrex
Sadly no activity at the Ram WE pin 10. I suppose its possible there is no ram access on boot, Regardless there is still no sound or display from the Vectrex.
The Usual Suspects
So it looks like the CPU , the 6522 or the Rom and thats just the logic board. I suspect more issues on the power board but the voltages are being supplied correctly. The CPU has got an intermittant fault with the pin 32 signal but after a couple of resets it sttles down so I’m hoping it is working when the signals are stable but will need to be replaced or at least socketed.
This Very Dead Vectrex Repair is now more undead but the repairs continue. I’m going to look for more clues and report back soon.
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