The more I think about it, the more it looks like a hardware problem with DMA circurity.
The DMA functionality is built into the chipset now, and AFAIR it is also reponsible for the RAM refresh via channel 0, so it can't be completly broken. If anything is wrong I'd start with ISA slots and signals, DMA 2 and IRQ 6.
But even if there is something wrong it does not explain why no BIOS (other than the original one) is working properly - or at all in fact.
Deunan wrote on 2023-07-25, 09:47:If anything is wrong I'd start with ISA slots and signals, DMA 2 and IRQ 6.
That's exactly my plan... 😒
etected by the ROM?
Deunan wrote on 2023-07-25, 09:47:The DMA functionality is built into the chipset now, and AFAIR it is also reponsible for the RAM refresh via channel 0, so it can't be completly broken.
Predator99 wrote on 2023-07-25, 10:09:What is the problem now? Did you configure XT-IDE to a valid base adress for your controller? Is the CF or HD detected by the ROM?
I think my 'small victory' with malinov card confirms my worries 🙁
I've sucessfully BOOTed DOS, set CMOS parameters and confirmed that FDD doesn't READ anything .
LED on all the time?
I had a similar case recently with a 386 mainboard. Video, keyboard etc. all working fine, but I couldn´t boot from floppy or hd.
The reason was a missing DRQ2 signal from the chipset - probably blown by a short when someone had taken out an ISA card while the system was still running.
Predator99 wrote on 2023-07-25, 16:36:Looks good, I would check this as working.
Is your Floppy cable drilled? If not its drive B. Is the LED on all the time?
Oh man, what did I do to deserve such questions 😉
Of course the tape is interlaced, and of course, it is not inserted backwards.
I've taken the picture immediately after the message about failed read when the LED was still on...
majestyk wrote on 2023-07-25, 17:23:I had a similar case recently with a 386 mainboard. Video, keyboard etc. all working fine, but I couldn´t boot from floppy or hd.
The reason was a missing DRQ2 signal from the chipset - probably blown by a short when someone had taken out an ISA card while the system was still running.
Thanks for the info !
I'll investigate this matter... soon :]
Locutus wrote on 2023-07-25, 18:07:Oh man, what did I do to deserve such questions ;) Of course the tape is interlaced, and of course, it is not inserted backwards […]
Predator99 wrote on 2023-07-25, 16:36:Looks good, I would check this as working.
Is your Floppy cable drilled? If not its drive B. Is the LED on all the time?
Oh man, what did I do to deserve such questions 😉
Of course the tape is interlaced, and of course, it is not inserted backwards.
I've taken the picture immediately after the message about failed read when the LED was still on...
This post is a breach to the community standards you agreed on when signing up. Predator99 have tried to help you through multiple posts in this thread. The way you worded that reply, you came across as dismissing his question and belitteling him. We encourage everyone here on VOGONS to participate and attribute whenever possible, and nobody should run the risk of getting ridiculed or dismissed because someone else saw your post as a "stupid question or obvious suggestion".
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vetz wrote on 2023-07-25, 21:02:Locutus wrote on 2023-07-25, 18:07:Oh man, what did I do to deserve such questions ;) Of course the tape is interlaced, and of course, it is not inserted backwards […]
Predator99 wrote on 2023-07-25, 16:36:Looks good, I would check this as working.
Is your Floppy cable drilled? If not its drive B. Is the LED on all the time?
Oh man, what did I do to deserve such questions 😉
Of course the tape is interlaced, and of course, it is not inserted backwards.
I've taken the picture immediately after the message about failed read when the LED was still on...This post is a breach to the community standards you agreed on when signing up. Predator99 have tried to help you through multiple posts in this thread. The way you worded that reply, you came across as dismissing his question and belitteling him. We encourage everyone here on VOGONS to participate and attribute whenever possible, and nobody should run the risk of getting ridiculed or dismissed because someone else saw your post as a "stupid question or obvious suggestion".
If you have any feedback or questions, please send a PM.
I guess you have missed ";)" at the end of the sentence...
majestyk wrote on 2023-07-25, 17:23:I had a similar case recently with a 386 mainboard. Video, keyboard etc. all working fine, but I couldn´t boot from floppy or hd.
The reason was a missing DRQ2 signal from the chipset - probably blown by a short when someone had taken out an ISA card while the system was still running.
I've confirmed the "DMA problem".
In my case, DACK2 is 'missing' 🙁
yellow: DRQ2 line
blue: DACK2 line
Locutus wrote on 2023-07-26, 20:57:I've confirmed the "DMA problem".
In my case, DACK2 is 'missing' 🙁
DMA is handled by the 206 chip. It might be that it doesn't see the DRQ so doesn't respond with DACK.
I've noticed that these older mobos tend to have issues with vias, they crack due to flexing the PCB and/or age and heat cycles (could also be a particular via that was weak right from manufacturing). So first trace these signals, there should be a direct connection between 206 chip and the pins on ISA slot. Do note that a break can happen between ISA slots so always check both first and last to make sure. Assuming these chips have standard pinout you are looking for pin 73 and 82 (but these have pin 1 at the dot, which is in the middle of one side). And it could also be a problem with the socket.
If all else fails you might need to replace the 206 chip. These can die because of the direct connection to ISA slots, some sort of a short on a card can take the I/O pins out (while leaving the rest of the chip functional).
Deunan wrote on 2023-07-26, 21:40:DMA is handled by the 206 chip. It might be that it doesn't see the DRQ so doesn't respond with DACK. […]
Locutus wrote on 2023-07-26, 20:57:I've confirmed the "DMA problem".
In my case, DACK2 is 'missing' 🙁DMA is handled by the 206 chip. It might be that it doesn't see the DRQ so doesn't respond with DACK.
I've noticed that these older mobos tend to have issues with vias, they crack due to flexing the PCB and/or age and heat cycles (could also be a particular via that was weak right from manufacturing). So first trace these signals, there should be a direct connection between 206 chip and the pins on ISA slot. Do note that a break can happen between ISA slots so always check both first and last to make sure. Assuming these chips have standard pinout you are looking for pin 73 and 82 (but these have pin 1 at the dot, which is in the middle of one side). And it could also be a problem with the socket.
If all else fails you might need to replace the 206 chip. These can die because of the direct connection to ISA slots, some sort of a short on a card can take the I/O pins out (while leaving the rest of the chip functional).
Thanks for your answer.
I rather rule out bad contact in the base, as I gave it a thorough cleaning which included taking out all the ICs.
Hopefully, checking traces will reveal the cause...
Do a continuity check from that pin to one of ISA slot. Then red on ground, black probe on DACK2 with meter in diode mode. What does diode voltage drop reads like?
Otherwise replace 206 chip. It can be any 206 chip. SiS, etc. I would avoid CHIPS. 😀 The one I replaced was 206 by CHIPS too back in the day on a American Megatrends motherboard revived it.
Cheers,
Great Northern aka Canada.
pentiumspeed wrote on 2023-07-27, 00:51:Do a continuity check from that pin to one of ISA slot. Then red on ground, black probe on DACK2 with meter in diode mode. What does diode voltage drop reads like?
Otherwise replace 206 chip. It can be any 206 chip. SiS, etc. I would avoid CHIPS. 😀 The one I replaced was 206 by CHIPS too back in the day on a American Megatrends motherboard revived it.
Cheers,
BAD NEWS 🙁
I've done continuity / shorts / pull-up resistors check on ISA bus - all looks very good.
DMA2 signals directly on 82C602 pins look the same as on ISA.
I'm afraid, it is time to look for a new 82C602.... 🙁
If I use 82C602 from another manufacturer, will it still be "CHIPS" mainboard ? 😉
You are golden - 82C206 can be found everywhere, in my case I´m looking for a super rare SL82C362SX....
Ways to safely transplant / replace 160-pin QFP chips
Btw - are you happy with your DS4024? I recently nearly ordered one, but wanted to make sure first it can handle 133, 166 and 200 MHz.
Locutus wrote on 2023-07-27, 15:12:DMA2 signals directly on 82C602 pins look the same as on ISA.
82C206 is pretty standard. Except Suntac chips, I mean these work the same too but the pinout is different and the chip packages are more unusual (hence why I gave you wrong pin numbers, I didn't double-check it with actual datasheet).
That being said, you are not done testing this particular chip just yet. You need to also check:
1) if there is clock on SYSCLK (21) - should be 8MHz
2) if there is activity on HRQ (69) after DREQ2 goes high
3) if there is activity on HLDA (73) after DREQ2 goes high - skip if test 2 fails
This would help narrow down what exactly has failed, is the DREQ ignored (input busted) or is the driver on DACK pin shot. In the latter case it might kinda work if you add pull-down resistor of some 1k to DACK2 line (assuming that of the pair of 2 output transistors the one that drives low is now dead). The actual resistance is to be determined by experimenting - you want the pulled signal to be still well above the 2V minimum TTL treshold when inactive, but pull as hard (thus as fast) as possible when the low signal should appear. Do not go below 100 ohm, and values close to this are already not safe for long-term operation but then again this 206 is suspect anyway.
With some luck, if only the DACK2 output can't drive low, this trick might just work - at least until you get a replacement. But test signals first, for test 2 and 3 you want to trigger on DREQ2 but monitor the pin in question.
DACK2 might be just "slightly" damaged, it´s between IRQ3 and TC (both TTL) so a short caused by a tilted ISA card is not a big deal.
In my case it was DRQ2 that´s between -5V and -12V. A tilted card will wreak havoc on the output stage.
majestyk wrote on 2023-07-27, 15:30:You are golden - 82C206 can be found...
Deunan wrote on 2023-07-27, 16:17:82C206 is pretty standard. Except Suntac chips...
"Fortuna favet fatuis..." 😉
I found almost full family of NEAT chipset (including 82C602) in my shack... no recollection when and where did I get it from 😳
Veni, Vidi, Booted from A:
majestyk wrote on 2023-07-27, 15:30:Btw - are you happy with your DS4024? I recently nearly ordered one, but wanted to make sure first it can handle 133, 166 and 200 MHz.
It's more than enough for me and as most Rigols... it's easy to 'hack'.
Currently it is 350Mhz & full options...
Does anyone know the purpose of the LED near keyboard adapter ?
It was blown but I see there voltages around 0.5V so no chance to lit it..
Anyway, I consider the case successful.
Thanks to everyone who motivated me with answers and advice, apologizes to all who found my sense of humor
'too crude'.
Time to play with "dead" ST-157A...
