Got a JVC hc-7e worked at first but now refueso to power on

Page 2/4
1 | | 3 | 4

By Sebastian Blanco

Rookie (23)

Sebastian Blanco's picture

18-03-2016, 03:06

Alexey i don't own an osciloscope theres any cheaper alternative to get this than purchasing one?, a logic probe could be enought maybe you know about something i can get on ebay.

By Wierzbowsky

Guardian (3541)

Wierzbowsky's picture

18-03-2016, 03:08

Some multimeters can measure frequencies, which one do you have?

By Sebastian Blanco

Rookie (23)

Sebastian Blanco's picture

18-03-2016, 03:12

By Sebastian Blanco

Rookie (23)

Sebastian Blanco's picture

18-03-2016, 03:14

I got a very simple one don't have any than AC/DC DCA and ohmeter.

By Wierzbowsky

Guardian (3541)

Wierzbowsky's picture

18-03-2016, 03:56

I am not sure what else can be done with just a simple multimeter. Can you describe what happens when you power the computer on? What happens when you reset it? Does it work with any cartridges? Did you try to get a picture from all available outputs (RF, Monitor, SCART)? Try to measure the voltages on R, G and B outputs of SCART and also on all pins of the Monitor connector.

Do you have a cartridge with external RAM?

By RetroTechie

Paragon (1563)

RetroTechie's picture

18-03-2016, 18:32

Sebastian Blanco wrote:

(..) and most of the ics on the board i was unable to get a pinout or even get what they are exept the easy ones like de ttl logic gates z80 etc

Try harder! Tongue

LH0080 is the Z80 CPU.
AY-3-8910A is a very well known soundchip (the "PSG"). Also known as YM2149.
M5L8255AP is Intel 8255 equivalent (the "PPI"). Even has its own Wikipedia article
Chip with the cooler on it will be the VDP. TMS9918A, TMS9929 or similar. Some small differences in function & pinout, but pinout is almost the same for all those variants.
HD27L019 is probably some kind of custom IC. Don't count on finding a pinout or datasheet for that anywhere. :( But given discrete PSG, PPI and other logic in the machine, there won't be much interesting stuff in it. Maybe some I/O address decoding, slot select logic or whatever.
YM2301 - sounds interesting but I'd bet it's a regular 32K*8 ROM with standard pinout.
HA11720 - probably a composite video encoder. Couldn't find a datasheet.
M5223L is some dual opamp. Datasheet here.

For parts where you have a pinout, it's easy to check connections to other IC's using a multimeter in low-range resistance setting. <1 Ohm or so = connection. Much higher = no (direct) connection.

Lacking a scope or logic probe, I'd try and find an external RAM cartridge + game cartridge and plug those in @ the same time. Might be that some RAM chip(s) has died and prevents the machine from booting.

Also, can you check how reset signal on various IC's responds to pressing the reset button? Easiest is if someone can give you a hand. You put multimeter on low voltage DC range, black test pin on a GND point, red pin on one of:
Z80 pin 26
VDP pin 34
8255 pin 35
Make note of voltage, have your helper press the reset button, see how voltage on IC pin responds, and make note of that too. Repeat for all points where you know an IC to have a reset input. Please post results?

By Sebastian Blanco

Rookie (23)

Sebastian Blanco's picture

01-04-2016, 15:07

Thanks guys for your replys Alexey and RetroTechie, before tuching anything more i like to test was was suggested before and use a ram rom cartrige to check. Today i received my mega sd flash + ram cart. Inserted it and know the computer works ! i can see the msx dos prompt on screen! Big smile. So this means problem lays on the rom or the ram ?.

By Wierzbowsky

Guardian (3541)

Wierzbowsky's picture

01-04-2016, 15:19

Most likely RAM is indeed broken. Not VRAM, but normal RAM. As you have MegaFlashROM, copy the RAM testing program (testram.com) to the card and run it from DOS. It should show you if your main RAM is broken.

By Sebastian Blanco

Rookie (23)

Sebastian Blanco's picture

01-04-2016, 16:31

Gonna test that later, thanks Alexey Big smile.

By Sebastian Blanco

Rookie (23)

Sebastian Blanco's picture

03-04-2016, 01:29

Alexey where i can find the testram.com program searched on google but all the links are broken.
Also the mb8118-12 are the ram or the tmm4164ap-15 vram ? not sure what one is what.

Page 2/4
1 | | 3 | 4