During my Hypersport’s repair I discovered a problem with the display of my Commodore 1084S monitor. Notice blue missing for “3 LONG HORSE” and “7 POLE VAULT”.
This will be the third time I’ve performed a repair on this old monitor which I’ve had since the early 90s for my Amiga 500 and 2000. At first I would suspect the AV7000 Supergun as the culprit. But subsequent tests would prove otherwise.
There’s definitely a better picture with composite or svideo from my c64 and Atari 8 bits but there seems to be a problem showing blue on the RGB input even though some blue is there ( turquoise , cyan.. etc ) in other images. Adjusting the blue gun and turning up the contrast just makes the backgrounds in Puzznic more blue. Where blue is supposed to be on the screen, it seems to not be present as though the signal were being cancelled out. With no RGB signal to the monitor at all, it defaults to a blue screen instead of a white one.
Apologies for the sync bands.
I suspected the neck board transistors, so I pull out the one responsible for blue and tests with my multimeter show it’s fine. I even swap the transistors around to see if the problem would move to the other gun…. but it doesn’t.
I found this really good post on eab [ English Amiga Board ] by Loedown
IC502 TDA 3505 pins 12, 13, 14 are RGB in from Euro Connector /SCART, check voltages there to begin with when inputting a perfectly white screen. Then follow the voltages through to transistors TS604 – 606.
The schematic shows the analogue inputs go directly from the RGB connector to the Philips TDA3505 IC via some 100nf caps. Pins 12,13 & 14 are the input RGB signals. I measured 4.3v for red and green but 9.1v for blue. That seems a little too high for blue and the schematic indicates 4v for those signals.
I order some TDA3505s on eBay from atarifreakz and my package arrives a few weeks later.
Not wasting any time. I replace the chip and the picture is now perfect!
The Taito logo and blue shadow around the Puzznic logo is now visible. Notice the bricks and backgrounds are also showing up right compared with the previous screenshot.
This fantastic monitor has been on my test bench for as long as i’ve been in this hobby and its been a great little work horse.
I powered it up the other day to test something and noticed the upper half of the screen had what I would describe as thick scanlines whereas to lower half of the screen looked a little compressed.
I hooked up my NES to it and the problem was a lot more apparent
Keep you eye on Luigi when he jumps to the top of the screen. As he moves up he gets longer
Asking a couple of people quickly, they all recommended changing the capacitors. The ‘shotgun’ approach isn’t really something I like doing as I like to understand what would cause issues before I randomly poke around but monitors are not my strong point so I started ESR testing in-circuit.
All the capacitors I checked were perfect with really low ESR values and all the capacitance readings were within spec. All except for one little capacitor, C306. This is a 47uF 25v capacitor and is connected to pin 12 of the vertical deflection circuit (TDA1670A)
I tested the capacitor out of circuit and confirmed for sure it was actually bad.
With the monitor taken apart I hooked up the Muter BMR95 to the tube to check the condition of the guns
A tube can usually be identified by the label that is on the back of the tube
E2940B22 is the one we want. Next we cross reference this to the supplied manual to find which adapter we need to use.
Adapter 808 is the one we need for this tube.
All hooked up
The guns aren’t too bad and certainly no need to attempt any cleaning or rejuvenating. Sometimes this can cause more harm than good. I have a spreadsheet prepared too as outlined in the BMR 95 manual to give a better indication of the life expectancy of a tube but i’ve not included it here.
With all that done it was time to test the monitor again
All seems to be fixed again and im happy with that.
You can see the stretching better with a picture comparisson
Before
After
Never underestimate the importance of a single capacitor!
Had this chassis for a long time sat in my loft. Its never worked properly and testing it now it doesn’t do anything.
Taking a good look at the chassis showed that quite a few capacitors had been leaking and testing random ones with the ESR tester revealed plenty more bad ones.
As it was in a poor state and also seeing as it is my first attempt at a monitor repair I opted to replaced pretty much every cap I could and do a clean up along the way.
I removed all the caps and tested each one that came out. Here is a list of the ones I found to be bad:
C958 – 47uF 16v
C956 – 680uF 10v
C457 – 10uF 50v
C459 – 22uF 50v
C561 – 47uF 16v
C451 – 22uF 50v
C222 – 22uF 50v
C201 – 47uF 16v
C203 – 47uF 16v
C955 – 180uF 25v
C953 – 47uF 160v
C513 – 10uF 250v
The electrolytic capacitor on the neck board was also bad.
Also found resister R585 (120k ohm) was damaged.
I ordered up the caps and cleaned up the PCB.
I then turned my attention to the remote board.
This had two pots missing but had a couple of different ones hacked in their place and the smoothing capacitor was also leaking. I found some 10k Alps potentiometers on eBay so ordered a couple of those too.
The existing pots look in bad shape but they check out OK and operate quite smoothly so ill leave them alone for now.
A few days later all my stuff had arrived from Mouser and I was ready to put this thing back together.
I fitted it back into my spare 29″ tube and fired it up for the first test.
With a bit of tweaking I got the decent picture. The photo doesn’t really do it justice but I’m pleased with the results.
In my previous repair I replaced a single capacitor to get the monitor working but this fix would prove to be temporary and only last a couple of months before something would go horribly wrong. The monitor is over 20 years old after all, so that was to be expected.
Several weeks ago I observed the monitor switch off for a split second and then back on, I thought this was strange but I knew something inside was on the way out. Since then strange lines would appear on the screen for a few minutes after power up.
And more recently, I was in the middle of playing SSF2 when the monitor totally crapped out on me all of a sudden, the screen went blank and the power led went off. There also was a high pitched whine coming from the monitor which is common when the FBT dies in these monitors, or so I read on the various C= forums. When powered off the high pitched whine would gradually decrease in pitch until it was no longer audible.
On to the repair. After opening the back of the monitor it was important to take the necessary precautions. All parts and tools were placed against the wall away from my work area ( the floor ) to create a safe working environment and prevent injury or damage to any components. I don’t have a large enough work bench so this was the best I could do with what I have.
Tools used for this repair
flat head head screwdriver, automotive gauge wire & alligator clips ( used to discharge the CRT )
240v 60w globe – series light bulb trick ( used to limit current ). 100w would have been better but I couldn’t find one.
DMM
Goot soldering station
Goot solder pump
60% tin 40% lead solder
Plenty of coffee & biscuits were consumed in the process
The next step was to discharge the CRT to avoid electric shock or worse. See my previous repair log for information on discharging CRTs. There is a link to a video by John’s Arcade which takes you through all the necessary steps to safely discharge it. Please do not do this if you are not confident or competent. You can get a nasty shock!
CRT discharged and anode suction cap removed from the tube. Discharging takes a fraction of a second with the screwdriver & attached wire from the screwdriver shaft to chassis ground of the monitor. Wait 10-15 minutes and repeat the discharging process to be safe or you can allow the flat-head screwdriver to maintain contact with the anode cap terminals and walk away for 15 minutes and do something else for awhile, like make a cup of tea or coffee.
Once discharged I then completely removed the FBT ( AT2079 37591 ) & the HOT ( horizontal output transistor – D1577 ). I also removed the neck board from neck tube which is required.
I wanted to test the power supply under some load. I soldered a 240v 60w lamp to the b+ ( to live ) and ground ( to neutral ) at the pads of where the FBT was installed. Pin 3 is b+ and pin 11 is ground.
At least the power supply section looks good with the load. I measured 130vdc across the cap at 2451.
I decide to look at the HOT which can also fail and take out the FBT in the process.
The D1577 HOT looks good to me but I have already ordered a spare just in case I need them. The BU508A is also suitable and was actually used in the same model. I ordered the BU508A
I’m confident the flyback is bad. I ordered a hr7533 ( which is a suitable replacement for the AT2079 37591 ). Since I am in Australia I found a supplier of the LOPT at Wagneronline instead of ordering from abroad which is handy for us Aussies if you happen to be one and are reading this. https://www.wagneronline.com.au/hr7533/9/ps/
If you have the earlier version of the 1084 shown below with the on/off switch on the front ( 1084S-P ) then the replacement flyback is the hr7506 which Wagneronline stocks as well.
24/6/2015
Wow that was fast shipping, 1 day from Sydney. So I really couldn’t wait to start working on the monitor this afternoon.
The next step was to remove the wires from the FBT to the neck board. To do this I had to de-solder and remove the RF shield first.
One of the wires from the old FBT to the neck socket snapped, so I had to remove the neck socket from the panel to remove the broken wire, no big deal 🙂
The socket had to come apart to get the small piece of wire out. With patience I succeeded in getting the wire out without destroying the socket.
After re-assembling the neck panel and soldering the two wires from the FBT to it, I soldered the 7 pins of the FBT to the main PCB. Then soldered in the new HOT and attached the clamp which holds the HOT in place so that it has good contact with the heat-sink, getting the HOT into that tight space was difficult and frustrating to say the least but I succeeded eventually.
Moment of truth has arrived. I powered on the monitor with SSF2 running and was delighted to hear no high pitched whine sound however, the display was so bright that the CRT was blinking. I adjusted “screen” on the flyback until the blinking stopped and I could see faint text on the screen. I put the game into test mode and selected the dot hatch pattern and tweaked “focus” until I could get the display as sharp as possible. I then adjusted the “screen” to get the brightness where I wanted it & then finished off by tweaking “focus” once again.
Happy with the results. The strange lines I described earlier are now gone and the display has never looked better. I re-assembled the monitor and I plan to play a few more rounds of SSF2 tonight.
Recently I finally got my first arcade cabinet from my friend ‘robotype’;
For the uninitiated the Astro City is a compact sitdown cabinet released from Sega in the 1993.It’s by far the most popular cabinet in Japan.It mounts a wide 29″ 15/24KHz monitor (Nanao MS8, some have Nanao MS9), its interface is JAMMA so widely compatible with most arcade PCBs.
After redone all the internal wiring and adapted the powering to 100V (main electricity in my country is 230V), I turned it on for the first time and I got a vertically crushed screen:
First thing I done was trying to adjust the vertical size through the pot on the remote board:
but I was not able since the pot was jammed.When I desoldered it, it fell off in pieces.The exact part is a 10KOhm manifactured by ALPS quite impossible to find nowadays so I opted for a generic trimmer:
With the new pot fitted I was able to correctly stretch the image vertically:
But the image was not stable, sometimes it crushed to become a horizontal line so I decided to furher investigate taking apart the chassis (NANAO MS9-29T model).First thing I’ve done was checking all the capacitors in-circuit with an ESR meter and I was able to found one bad which was clearly leaking and whose ESR was out of range of my meter (0-99 Ohms) :
Replaced it fixed all issues.
P.S.
For those interested I compiled a capacitor list of the NANAO MS9-29T chassis.You can view it from here (or download from site)
