Philips VG-8235 Burns fuse

Master (177)

12-11-2020, 08:32

Hello,
I Just recently bought a VG8235 in original condition from ebay. Of course I tried to switch it as soon as i got the package. Unfortunately the fuse burned immediately after powering the msx on. I did'nt really expect too much as it is an old machine and just opened the computer and now cleaning all possible parts. In general everyhing looks very nice at the inside except for the drive belt which had broken down into little pieces. Also the chassis is on very tidy condition
My questions:
1. Is there any known usual reasons for the fuse to burn straight after power on or should I just look for the general reasons for the fault?
2. My plan is to enchance the msx with carnivore2+opl4 and I'm using scart -output for video, so could I just take out the cables for old diskdrive and remove also the cable for the board with printer in, tv in, and monitor in. Does msx need them to be attached to run with?
br, xnr

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By Briqunullus

Hero (665)

12-11-2020, 09:26

Xan0ri wrote:

so could I just take out the cables for old diskdrive and remove also the cable for the board with printer in, tv in, and monitor in. Does msx need them to be attached to run with?

Sorry, can't help you with your fuse question. However, I can confirm the 8235 runs just fine without the diskdrive attached. No idea about the little board with the printer, tv and monitor connectors, but I suspect you can leave that out without problems as well.

By the way, which type 8235 do you have? It is a 8235/00 (or any number below 20) or a 8235/20 (or any higher number)?

By Xan0ri

Master (177)

12-11-2020, 10:52

Briqunullus wrote:

By the way, which type 8235 do you have? It is a 8235/00 (or any number below 20) or a 8235/20 (or any higher number)?

Hi, and thanks for the tips! I'll remove the diskdrive at least, maybe even the fuse problem originates from it. My msx is VG8235/00. ..Is there any major differences with the versions?

By meits

Scribe (6542)

12-11-2020, 11:41

Nu clue about the fuse. Your PSU might be broken. Got any way to measure voltages? Whatever the answers, I can't advice you on that, but there are guys around here who can.

You will need the print with the monitor/printer on it. If you remove this there will be no sync on the rgb which will make your video dance like crazy.
I'd just leave the nonfunctional drive in, just to keep the structural integrity in tact and less holes to let dirt in.
If the noise a beltless drive makes bothers you, better just disconnect the cables from the drive and leave it with that.

Xan0ri wrote:

My msx is VG8235/00. ..Is there any major differences with the versions?

Except for the outside there's not much the same between the both. Scroll a bit through these two PDF files to compare a bit.

By Briqunullus

Hero (665)

12-11-2020, 13:10

They are very different indeed. The 8235/00 needs a hardware fix on its internal memory mapper.

By Jipe

Paragon (1614)

12-11-2020, 14:03

for verify the power supply deconnect CN11 at the mainboard and CN03 at the Floppy Drive

retry power supply and check if the fuse burned

if the fuse is no burned the power supply is good, verify +5v +12v -12v

if the fuse is burned check the bridge and the capacitor on power supply

By Xan0ri

Master (177)

12-11-2020, 18:22

Jipe wrote:

for verify the power supply deconnect CN11 at the mainboard and CN03 at the Floppy Drive

retry power supply and check if the fuse burned

if the fuse is burned check the bridge and the capacitor on power supply

Got some new fuses and tried with no extra stuff connected. -> It burns. So, it must be a faulty PSU. What capacitor you mean or all of them? And what certain bridge, or all of them? Sorry, for bothering with such noob questions, I guess my electric skills are a bit rusty nowadays. And I have a problem translating from england as well.

By Jipe

Paragon (1614)

12-11-2020, 19:53

warning on PSU you have 300v behind the bridge ( D1 2WD6 on schematic )
the capacitors are C4 C5 100µF
this is a switching power supply and is complex

By Xan0ri

Master (177)

12-11-2020, 20:39

Jipe wrote:

warning on PSU you have 300v behind the bridge ( D1 2WD6 on schematic )
the capacitors are C4 C5 100µF
this is a switching power supply and is complex

Yes I understand that, and I'm aware of the risks & high voltage.
The big capacitors on the board (c4, c5) actually look ok at least, but I'm doing measurements with resistance meter and cannot get a real value. Only can see that they do load (because of the measurement). Also bridge at least looks good but maybe I'm not skilled enough to take measurements on it.

By Xan0ri

Master (177)

12-11-2020, 22:27

I got the MSX to boot up! ..Or at least to stay on stable. I ended up making an external power supply out of typical modern ATX-powersupply.
Now my problem is that actually I only get a black screen after switching on. No boot logo or anything.
Disk drive is not attached but the board with printer, RF & Monitor plugs is connected to mainboard.

I would appreciate any ideas how to continue or what to try fixing next.

Here is a picture of the project in its current state: :--D

[link]https://ibb.co/BNYvpKY[/link]

By meits

Scribe (6542)

12-11-2020, 22:57

Is there sound? Give it a short while to boot and then press ctrl+G to hear a beep.
Did you see a battery on the mainboard? if so, press shift+F1 in the black screen (should set colors to default).
Do you have a game cartridge you could test?