AndyZX wrote:If I have to identify THE problem it is about loading from microdrives as described above.
My issue 6 board has the resistor mod so your issue 5 must have them. See here on the bottom left of the picture at the bottom of the page. viewtopic.php?f=8&t=3065&start=10
They are on the RAW lines for the micro drives to fix a borderline problem.
Pr0f wrote:The picture shows the decoding IC for the ROM's is not fitted - you have only a socket, this means the board's wire jumpers
No mention of this so is that a preconfigured jumper block that gets soldered in like a socket but contains shorts for required jumpers?
Is the resistor mod on the top of the chip required or is it different on a series 5 board and fitted somewhere else?
If you look at the picture of the motherboard - between the ROM closest to where the Microdrives would be (bottom ROM socket in the picture - and the empty 14 pin socket - there are positions for 6 jumper wires - currently 3 are fitted as 0 ohm resistors (one single black band). On an issue 5 board, these jumpers in conjuction with an LS logic chip that can (it isn't always fitted) be fitted can allow various combinations of ROM/EPROM to occupy the 2 ROM sockets. The setup shown mirrors what would be present in an issue 6 board - namely 2 identically wired 28 pin ROM sockets - the standard AH, JS, or whatever ROMS are fitted are enabled using opposite logic polarity - so one is enabled when the Address line is low, and one is enabled when the address line is high - the result is that 2 ROMS can be wired in parallel - as only one will be active - this is why you sometimes see stock ROM chips wired piggy back and present in only one socket. You can treat the sockets as identical. This means Minerva on the carrier board will work in either socket.
I suspect the issue you are facing is related to the vDrive and Microdrive wiring and some interference between them. Do you have pictures of that end of the board - showing how the vDrive is connected?
Pr0f wrote:If you look at the picture of the motherboard - between the ROM closest to where the Microdrives would be (bottom ROM socket in the picture - and the empty 14 pin socket
Thanks. I was confused by the odd looking empty socket that my issue 6 doesn't have. If the board is rigged as an issue 6 ROM system does it mean the RAW line resistors are fitted somewhere else instead of on top and soldered to the pins of the 40 pin chip?
The board itself is issue 5 - so that BIAS resistor fix is still needed - as the resistors are not elsewhere on the board. The service manual - available on Dilwyn's site - has a list of all the mandatory modifications I believe.
Pr0f wrote:The picture shows the decoding IC for the ROM's is not fitted - you have only a socket, this means the board's wire jumpers
No mention of this so is that a preconfigured jumper block that gets soldered in like a socket but contains shorts for required jumpers?
Is the resistor mod on the top of the chip required or is it different on a series 5 board and fitted somewhere else?
If you look at the picture of the motherboard - between the ROM closest to where the Microdrives would be (bottom ROM socket in the picture - and the empty 14 pin socket - there are positions for 6 jumper wires - currently 3 are fitted as 0 ohm resistors (one single black band). On an issue 5 board, these jumpers in conjuction with an LS logic chip that can (it isn't always fitted) be fitted can allow various combinations of ROM/EPROM to occupy the 2 ROM sockets. The setup shown mirrors what would be present in an issue 6 board - namely 2 identically wired 28 pin ROM sockets - the standard AH, JS, or whatever ROMS are fitted are enabled using opposite logic polarity - so one is enabled when the Address line is low, and one is enabled when the address line is high - the result is that 2 ROMS can be wired in parallel - as only one will be active - this is why you sometimes see stock ROM chips wired piggy back and present in only one socket. You can treat the sockets as identical. This means Minerva on the carrier board will work in either socket.
I suspect the issue you are facing is related to the vDrive and Microdrive wiring and some interference between them. Do you have pictures of that end of the board - showing how the vDrive is connected?
Yes of course, here is the picture of microdrives and vMap. Let me know if you need a zoom of any item.
Can you check that the vMap and Microdrives is installed correctly.
Try accessing the vDrive without the vMap installed, you will need both microdrives installed to establish the link from the 8302 to the external Microdrive connector.
Or without micrdrives installed, connect a link wire from MDV1 connector Pin 1 to MDV2 connector Pin 2, to link the connection from ZX8302 MDSELDN, pin 34 to 4A on the microdrive external connection. The vDrive can only access MDV3-8 without vMap.
Its seems that the MDSELDN line goes in a serial line of:
AndyZX wrote:If I have to identify THE problem it is about loading from microdrives as described above.
Until all the modifications are done to the issue 5 board to bring it up to spec like RAW line resistors and it works as a standard QL there is no point in looking at upgrades is there? Just a thought that if you are running on 230V EU with an old spec PSU for 240V the output will be lower and that could drop things out of spec that may have worked in GB.
1) Bad Power supply or not enough power - may show up more often if the expanderam is installed as it will created an additional load - the difference between Minerva and the standard ROM's won't make much difference
2) Installation issue with the vdrive / vmap - the vmap is tricky to fit - it's ever so easy to break a wire from the standard Microdrive cables - may not be noticed when it's all back in the black box.
3) Bad Microdrive - these funky little tape drive units are getting old - it could be a film of dirt / dust on the capstan rubber that moves the tape past the head - a gently wipe with isopropyl alcohol should restore it, but the other possibility - is the felt within the Microdrive cartridge - this turns to dust or becomes hard over time - replacement would be essential for any attempt to read from them - you may also be suffering from degradation of the magnetic medium - these are getting on in age now. You could try downloading some of the MDV images from Dilwyn's site and test loading with the vdrive directly - if that works at least you know the basic Microdrive handling in the QL is working correctly and the issue is more likely to be the original Microdrives or their media.
4) It's likely you are missing some modifications - the resistor mod that Ruptor talks of really should be applied - it feeds -12v through some high value resistors to raw1 and raw2 - the modification sits on top of the ZX8302 chip - that's why it's noticeable you don't have it.
Guys, thank you were much, you are wonderful and advice very useful!
If I take a look back - I bought a QL nearly a year ago. It was tested and functional. MDVs were working fine, MDV1 was perfect, MDV2 more temperamental but still ok. Because I wanted to have a modern storage system, I installed vDrive and vMap as is usually suggested for the QL. Then some problems started - the use of the vDrive was also a bit "temperamental". Often it would not detect the boot file on MDV3 or a configuration file on the SD card. Later it would not detect an SD card, but this seems to be due to a low quality of the SD card (intenso).
The problem with MDVs came to the fore with an upgrade to Minerva when the storage system became inoperable (except for small Sbasic files).
The Exapanderam seems to be the least of a problem. Currently, a signal enhancer helps but I will go for a new adapter as suggested.
I see now that several hardware adjustments need to be made and the MDVs and vDrive (plus vMap) system need to be checked. Unfortunately I am not an expert in computer electronics. Had I known these problems before, I would have brought the computer with me when I visited London in June and go for repairs in the UK.
Question: Could anybody suggest an expert to take a look at my computer who is close to my neck of the woods on the continent (Slovenia)?
AndyZX wrote:Question: Could anybody suggest an expert to take a look at my computer who is close to my neck of the woods on the continent (Slovenia)?
What about a TV of HiFi repair shop? If you dig up the information for an issue 5 upgrade and give them just the PCB out of the box anyone with a soldering iron that can solder electronics can do it for you. Just a thought if you raise the mains voltage input to the PSU with a step up transformer (variac maybe) to recover the 5 or 10 volts lost the Microdrives & everything might start working again.
If the board is rigged as an issue 6 ROM system does it mean the RAW line resistors are fitted somewhere else instead of on top and soldered to the pins of the 40 pin chip?
