VG8000 and VG8010 problems - new to MSX

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By Wlcracks

Champion (430)

Wlcracks's picture

14-06-2017, 07:32

There is a lot of info on the VG8000. Every chip is very well documented. Mine VG8000 was blown by metal in the cart slot, all pins got all the voltages. I still could fix it. Due to no engines and array where used, this is the most simple computer there is to fix. All biggest chips are on sockets. All basic logic ttl chips. If you socket the RAM chips, having 2 machines there should be no problem. If you don't have the patience, vision on try and error method and the measuring tools like scoops logic analyzer etc, maybe this isn't for you.

By Lord_Zett

Paladin (807)

Lord_Zett's picture

14-06-2017, 16:15

its a realy poor build msx.

By hamlet

Scribe (3223)

hamlet's picture

14-06-2017, 18:35

It has a cheap keyboard but it is solid build with lots of socked ICs. Of course this will never be the main MSX to use, it has other specials you will love. I like to show my students this mainboard, build simple without engine.
A friend of mine bought one in 1986, because it was cheap this time. I already have had an 75P, but his parents did´nt want to spend to much money for my friends new hobby. We did a lot of typing listings on the 8010 and didn´t care about the rubbish keyboard. That days I remarked the 8010 as a ugly ducking, but today I really love the design, it has a futuristic touch like the G7000 consoles. Later in that decade computer got way much decorated but the 8010 expressed the pure 70s future imaginations.
Althought MSX computer did not sell as bad as we all thought (I read there was more MSX machines sold then Apple II, but I have to reinvestigate the source), there was no given technical layout design. So every company joined the standart was able to build their own MSX (that did´nt have to have much in common with other brand products) only have to obey the MSX specifications. Commodore also did a lot of revisions on their boards (wasn´t it about 16 different ones for the C64) but not one of the MSX machines was sold in such high lots like the CBMs. Especially not the 8010. It was not so much cheaper than the companies own competitor the 8020, which supports a real typewriter keyboard but lacked of so much other things (no printer port, less RAM, damn weird wired keyboard, unusable cursor keys and a bad video outut signal).
But that makes it shining among all those other computers nowadays. If I had to cut down my computer collection to five MSX, the 8010 would be in. How about you? What are your five favs?

Seen on

By calderone

Rookie (18)

calderone's picture

03-05-2020, 18:19

Hi gehtjanx,

Where you able to proceed on this VG8010 problem, or did you give up on it ?

I strong believe I encounter the same problem, my VG8010 does not start up and only shows me a black screen.
And on very, very, rare occasions, I also see, like you say, 'a bit of a "grid": black Screen with slightly Brown-ish grid graphics or so'.
But mostly the screen stays black. I cannot reproduce the scrambled graphics, but I must say, I only saw these lines when I had put in a game cart and with the DRAM board out of its sockets.
But still, it is very hard to reproduce, I only have seen this twice until now...

So I started reading through your history, and I'm also convinced it must be the memory RAM chips. You already tried and found a failed DRAM chip on the DRAM Board but still encounter the black screen problem.
Did you try to change the VRAM chips ? As I start to believe this could be the first problem, if VRAM is bad, you will have nothing on the screen, right ?

That would be my next step to test, to replace the 2 VRAM chips (TMS4416-20NL) and see if something appears on the screen.
I have ordered some RAM chips, both DRAM and VRAM chips (TMS4416-15NL & TMS4416-20NL), but it will take a few weeks before I would have them, as they come from China these days.

I also noticed that the VDP (TMS9129NL) becomes very hot after a while. I already tried to replace it with a spare one (was ordered a few weeks ago), but it still becomes hot and I still have the black screen.
Thats why I'm suspecting the VRAM's now.

By Manuel

Ascended (16956)

Manuel's picture

03-05-2020, 21:25

At the first time Bas Tilborghs and I were displaying MSX on the Vintage Philips Weekend in the Philips Museum in Eindhoven, we thought that the VG 8000 and VG 8010 that he brought were dead. There was no image coming out of them at all, but sound appeared to be working.
But then we had to go down for the photoshoot and we left the machines on (for whatever reason). When we came back 10 minutes later or so, there was image!

So, leave it on for a while (15 minutes at least?) and perhaps the problem will solve itself...

By calderone

Rookie (18)

calderone's picture

05-05-2020, 17:09

Hi Manuel, I tried your suggestion, but unfortunately nothing changed, the screen stayed pitch black. Sad

I also remeasured all voltages, I have measured them before but just to be sure, +5V and +12V are near spot on, but -12V seem to measure -14,5V. Nevertheless, when checking the schematics, I cannot find any component using the -12V ? I suppose this is for add-on hardware ? So I believe I can ignore this -14,5V ?

By sdsnatcher73

Paragon (1136)

sdsnatcher73's picture

05-05-2020, 19:04

Manuel wrote:

At the first time Bas Tilborghs and I were displaying MSX on the Vintage Philips Weekend in the Philips Museum in Eindhoven, we thought that the VG 8000 and VG 8010 that he brought were dead. There was no image coming out of them at all, but sound appeared to be working.
But then we had to go down for the photoshoot and we left the machines on (for whatever reason). When we came back 10 minutes later or so, there was image!

So, leave it on for a while (15 minutes at least?) and perhaps the problem will solve itself...

I confirm this. It has happened to me as well with a VG8010.

By calderone

Rookie (18)

calderone's picture

14-05-2020, 21:53

I have done some more testing and more troubleshooting on my VG8010.

First, I desoldered all DRAM's from the mainboard very carefully, 2x TMS4416-20 (VRAM) and 4x TMS4416-15 (RAM) chips.
I took my time to do this. On the internet there are good video's showing how you do this the right/good way.

And while waiting for the ordered DRAM chips, unfortunately it will take a while before they arrive, I was looking on the internet if a good DRAM testing device would exist. I found a bunch out there, but when it comes to testing 4416 DRAM's, the number drops significantly.
Finally I found my solution on this website:
A very nice German website about good old 8-bit computers whit lots of info. And the link to the actual Memory Tester site is this:
The latest revision, seemed to me (at this time), a bit of an overkill if I only wanted to test my 4416 chips, so I contacted this website, to see what was possible, as it mentioned that older (and simpler) revisions might still be available.
It was confirmed Rev. 3.1 was still available and was a good starting point to build myself a good DRAM tester for my 4416 chips.
So I ordered the board (only PCB possible) and the components elsewhere and started building. The tester worked as expected and when testing the 4416 chips, they all passed without finding any failures !?
Damn, I was expecting failed ram chips, but it seemed they showed all good! Nevertheless, I felt this step was not lost, as the DRAM tester will serve me many times in the future as it also can test other DRAM chips, even the more common 4116 chips, and others !
Also, I'm even considering to order a newer revision as these can also test SRAMs, eproms and many logic IC's.

So I will have to exclude the RAM chips in my search repairing this MSX.

After putting back the GOOD DRAM chips, now in sockets, the result was the same: a black screen !

So I started studying the schematics again. What could be wrong around the VDP (TMS9129NL) chip ? As I still believe it has something to do with this chip. VRAM's are good, what could be next? The schematics shows me that the video signals for the CVBS socket also goes through the PAL encoder board. This is the separate board, which I did not gave much attention, as I thought it was mainly for the PAL UHF TV signal. My mistake, as when I started to touch the, O so many caps, I got the 'scrambled screen' again. ... I found a way of reproducing the scrambled screen. Another step closer to the solution ?
Especially when I touch C821 on the PAL/CVBS encoder board, I'm getting again the 'grid lines' gethjanx was describing. Looking closer, it is a 100uF/10V elco which I had available, so I replaced it right away but, unfortunately, the problem stayed. Touching it, showed me the scrambled screen again.. Releasing it, black screen...

Looking even more closer, I measured the removed elco, it showed me a value of 46uF, where it should show 100uF !. Eeuhm, this is my second cap I removed and measured, they both measured half of their expected value! So, I'm starting to believe, strongly, I will need to re-cap all these old elco's. Also other discussions in this forum, points out this is a necessity. seems I have a next step in my troubleshooting ;)

By jltursan

Prophet (2316)

jltursan's picture

15-05-2020, 08:05

No idea if this model usually fails due dried caps; but indeed, if you want a full restoration, it's always a good idea to replace all electrolytic capacitors. About video problems isolation, check this thread:

By calderone

Rookie (18)

calderone's picture

27-09-2020, 16:22

Finally I got some major progress, but I'm not at the end yet! Let me summarize.

First I did re-cap all electrolytic capacitors on the main board and on the PAL/CVBS encoder board.
Many caps had halved in capacity over the years, so it was the right step to do.
Unfortunately, this did not solve the main problem, the msx stayed with a black screen.

So, I decided to simplify my troubleshooting and tried to remove unnecessary components (for now!):

- I disconnected the PAL/CVBS encoder board (desolder the ribbon cable from the main board) and connected a fresh GBS-8200 VGA converter board, which I believe it should work as well.
Also see this setup:
So I connected Y, R-Y and B-Y straight from the VDP to the GBS-8200 VGA converter board (Y, Pb, Pr inputs) with 470 Ohm resistors between signal and ground.
I used an old RCA cable with one side, 3x RCA connector and at the other end, I soldered breadboard cables with pins.
I did also solder some 'temp' breadboard wires on the ribbon through holes on the main board, Y, R-Y and B-Y from the VDP is available there, so no need to solder it on the VDP pins !!
So easy !
Power for this GBS-8200 VGA converter board is also taken from the ribbon through holes on the main board. Just solder some more breadboard cables onto +5V and GND and connect them to the breadboard.

- Also I removed the sometimes 'annoying' Memory Extender board, so in fact I degraded my VG-8010 to a VG-8000 (for now). Instead of 4x 4416 RAM, I'm left with 2x 4416 RAM (16K).
By doing this, I also needed to make some changes in the RAM traces. I checked the Service Manual for this. It is not that complicated.

Ok, after doing this, I'm left with the same black screen (now blue with the GBS-8200). But I'm starting from here now, with a simplified setup!

Next step, I checked all traces with my continuity tester, IC by IC, following the VG-8000/VG-8010 schematics. I made 'trace tables' for each IC.
Unfortunately I damaged some traces myself, by desoldering IC's, so I repaired them during this time consuming process. But I'm glad I did check the traces !
As a result, I found many faults in the VG-8000/VG-8010 schematics !!. Maybe I will open another tread to update on this.

So all traces are checked, power on: same black/blue screen.

Moving to the next step, I started measuring life signals on the board with my logic probe. First I started with the VRAM, but all major signals seems normal.
Then I focused on the sytem RAM. There I found some strange anomaly ! On 2 address lines A2-A3 (pin 11&12), I see no signal.
Checking the schematics, I can see these address lines are coming from a multiplexer IC 74LS157N (IC705 pin 7&9). Measuring the source address lines seems all ok.
So, this 74LS157N (IC705) might be malfunctioning ?? I have no spare available, so I ordered some from China but I had to wait a few months before they were delivered :-(

Finally, I replaced this 74LS157N (IC705) but, still, I only see a blue screen.

So I decided to continue with the signal testing on CPU, ROM, PPI, VDP, ...
On the 23256 ROM, for example, I see, I believe, more activity, /CE and /OE shows active pulsing, so this ROM must be working. But still I have nothing on the screen.
Then I turned around the main board, solder side up. Powered it on again and (with some luck?) I saw a frozen msx-basic screen.
Unfortunately I could not reproduce this again, powering up again is showing a blue screen consistently.

Is there still a broken trace ?? I checked them all or almost all ??

Gently bending the board, confirmed that it could be a broken trace, I could reproduce the msx-basic screen for a short time and only a few times.

Probably replacing the 74LS157N (IC705), did solve the main problem (Initializing) but is there still a connection problem ?

Thinking about it, I decided to clean the sockets with de-oxit spray. Many of the original IC's are socketed from factory.
If no change is seen after cleaning, then I could conclude it is a broken trace somewhere. If it should become better, maybe it is just oxidised connections in the sockets.
After the de-oxit, I see more and more msx-basic screens appearing, nevertheless I still see the blue screen as well. But I have the feeling I'm going to a better situation.
Finally I did a thorough cleaning with de-oxit on all available sockets and let it dry. After this cleaning, I see some more msx-basic screens appearing, which could be a good sign.
But I don't want to jump for joy yet !
Next, I removed all socketed IC's and checked the state of the pins. The IC sockets seems clean now but the IC pins still are showing a lot of oxide. So I decided to clean them with a very fine sandpaper.
I'm doing this very carefully, as I don't want to damage the pins for worse. Then I placed them back and it felt like the IC has more contact on the sockets.

Powering up the MSX now, seems to boot more often into the msx-basic screen than before !! But still not all the time.
Even a short test with a game cartridge seems to work !!
And the keyboard seems to work.

Unfortunately, my luck was short, the next day the MSX stayed with the blue screen again, so I believe there must be a broken trace or a bad connection somewhere ??
I will need to re-check all traces and signals again....
But I will not give up on it, now that I know there is still life in this machine ;-)

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