I've started this conversion a very long time ago. Also built in a SIMM memory expansion and then my 8280 did not boot. (I only heard the cassette relay click and that was it.) I've taken out the simm expansion already, managed to find some 64K x 4 memory bank chips to restore that to original but I would like to keep the v9958 inthere.

Has anyone on the forum here done the V9958 swap? I used the hans otten schedule back then but I see I have also cut two resistors (R166 and R167) which normally provide 5V to the VDP pin 26 and 27 but I can't see that in any description. Is this nescessary?

not necessairy to cut R166 R167
check
pin 27 -> ground
pin 21 -> +5V
pin 4 -> ground
click in the cassette relay -> no rom or no ram valid
put a 64k cartridge expension in a slot and see if MSX work
if work check RAM
if no work check rom or a wire cut

jipe how do you know this?

where did you get that info?

(just curious)

no manual no book just personnal experience and curiosity

just expand and repare more 8250 55 80 HB700 Turbo-R
expand -> no work -> search error -> often PCB wire broken when desold Ram

if you desold the ram inside the MSX and Insert external Ram in cartridge the MSX works perfectly
i don't try on Turbo-R i have a doubt because Ram is directly on R800

Quote:

not necessairy to cut R166 R167 check pin 27 -> ground pin 21 -> +5V pin 4 -> ground click in the cassette relay -> no rom or no ram valid put a 64k cartridge expension in a slot and see if MSX work if work check RAM if no work check rom or a wire cut

Does this also apply for the nms 8250? As I just built in a v9958 in my 8250 and the screen is not looking as I want. It is blue but not syncing correctly.
I did the following:
removed R166 and R167
wire from pin 4 to 20 and 27
and wire from pin 21 to 58

8250 and 8280 are same board
just video digit board is different
check all your wire around the VDP because then desold you can breaking one or many wire

Indeed I am already checking out all pins from vdp to other connections. As I had no sdip socket I soldered the new vdp straight into the pcb.
But I will also wire it according to your instructions. Hope it works out!

have you the schematic of 8250 ?
check wire one to one with a multimeter with beeper
no miracle with R166 R167 connecting -> is same working

I have the original service manual
at the moment one of the 2 pins of R166 / R167 is unconnected which is strange to me.
with the resistor in it is connected to at least something.

Unfortenately my multimeter has no beep ...

Well my machine works again. IEither I connect my rom not correctly so the msx logo is not displayed very well or something else is wrong.
Does someone have a good 2+ subrom for me? I downloaded the one from Hans0 Site in a 27c512 eprom ...

sure this rom work fine
you must added PORT F4 decoder for all function

http://www.msxarchive.nl/pub/msx/mirrors/msx2.com/hansoranje/F4-LatchenAdresdecoder.JPG

So without the F4 decoder the msx logo is not displayed correctly?
If so I need to get some ttl ICs

if the port F4 not added the MSX boot with blue screen (no logo) and go directly to basic

I have one more question, when I switch on the msx computer sometimes the screen is not correctly displayed.
The blue of the background is more darker and it looks like some sync is not correct. Allthought the text is displayed correctly.
When I switch off the machine a couple of times it is normal again.
Also when I have a game inserted (I tested with Space Manbow) the konami logo is not displayed correctly but the rest of the game everything is normal again. It looks like the v9958 is not initialized correctly.
I connected the v9958 I little bit different as I used the msx2+ sm to see how it was connected over there:
pin 4 -> 58 with a resistor of 10K in between
pin 21 -> 58
pin 27 -> 58
also the R166 and R167 are removed.
There was a 100nF capacitor on pin 20 and 21 and I removed that one to see if that made any difference but it did not.
Can someone help me with this?