Share your knowledge on these two classic MPCs
By LADiego Thu Nov 08, 2018 1:56 am
Hello Fam,

Does any one know the purpose of 2 resistors found under the removable cover on the underside of the Microtech pcd-25bh? Are they really needed?
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By JUKE 179r Thu Nov 08, 2018 2:31 pm
Can you post a pic of it?
They might be the SCSI resistor packs for termination... maybe...
By LADiego Thu Nov 08, 2018 10:36 pm
JUKE 179r wrote:Can you post a pic of it?
They might be the SCSI resistor packs for termination... maybe...


I have pm’ed pic. I am having a hard time posting pic.
By richie Fri Nov 09, 2018 1:32 am
LADiego wrote:I have pm’ed pic. I am having a hard time posting pic.


And responding to pm's ! I pm'd you a year ago about a card reader thing and still haven't heard back!
By LADiego Fri Nov 09, 2018 3:20 am
richie wrote:
LADiego wrote:I have pm’ed pic. I am having a hard time posting pic.


And responding to pm's ! I pm'd you a year ago about a card reader thing and still haven't heard back!


I just checked my pm just now and noticed you did pm me in oct 2017. I only have a total 5 pms since joining mpcforums. Not that it matters now and I am unsure if I responded but going to assume no, to answer your question, no I did not have a pic of McDisk power adapter. My apologies. Not sure if there is a e-mail notification when someone pms. Since I let juke know in a post, I will check my pm periodically for a response but again I am unsure if I will get an e-mail notification.
By richie Fri Nov 09, 2018 3:46 am
@LADiego no I never got a response. Do you not own the McDisk anymore?
By LADiego Fri Nov 09, 2018 5:34 am
richie wrote:@LADiego no I never got a response. Do you not own the McDisk anymore?


No. The drive failed and was passed along to someone who thought it could be fixed. Just before it failed, the drive worked intermittently (on and off). A real pain. And I switched to Microtech and it works perfectly.
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By JUKE 179r Fri Nov 09, 2018 9:51 am
LADiego wrote:
JUKE 179r wrote:Can you post a pic of it?
They might be the SCSI resistor packs for termination... maybe...


I have pm’ed pic. I am having a hard time posting pic.

Try using https://imgbb.com/upload to upload a pic and then post the link here.
By richie Sat Nov 10, 2018 5:21 am
Yes I believe those resistor flat packs are for termination. You'll see the same thing employed in the scsi2sd now as well.
By LADiego Sat Nov 10, 2018 6:34 am
Richie, Thank you for sharing your knowledge of the significance of these resistors. The card reader seems to work fine “without” the resistors with the mpc2000xl and s6000. This weekend I will test with an mpc2000 Classic which tends to be finicky. And I will try to locate someone locally with an mpc3000 to see if card reader works without the terminating resistors in the card reader. I am guessing the mpc2000 and the mpc3000 will generate issues due to missing terminating resistor pack.
By richie Sat Nov 10, 2018 6:40 am
@LADiego I wish I knew the values of the resistors but I'm out of ideas in that regard. I'm sure that they would be low values so if you can find out what the scsi2sd uses, that would be a very likely entry point or resolution man.

The S6000 has its own termination on the back, so there is that as well but I assume you are looking to do an internal install. For dual pcmcia card readers, I prefer to use them in an enclosure so I could utilize them by more than 1 device as I'm sure you're aware each slot has its own id. I think on default without no pin header they default to 0 and 1.

An alternative on the MPC 2000 or 3000 (as lame as it sounds) could be to plug a zip drive in the back and have the termination switch on. Or if you happen to be using a 50 pin cable with more than one port on it, you could get an internal terminator such as this:

Image
By LADiego Sun Nov 11, 2018 1:27 am
Richie, Thank you for thoughts on the resistor packs for pcd25b. The use of a scsi Zip drive in a daisy-chain with card reader and sampler is a good one. I did use this strategy with an older spyrus drive years ago and it worked. I will try this approach again. Thanks again.
By richie Sun Nov 11, 2018 4:53 am
@LADiego you're welcome man, glad to help.
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By 3K. Tue Nov 13, 2018 8:26 pm
richie wrote:I wish I knew the values of the resistors but I'm out of ideas in that regard.


Image

Termination can be passive or active. Passive termination means that each signal line is terminated by two resistors, 220 Ω to TERMPOWER and 330 Ω to ground. Active termination means that there is a small voltage regulator which provides a +3.3 V supply. Each signal line is then terminated by a 110 Ω resistor to the +3.3 V supply. Active termination provides a better impedance match than passive termination because most flat ribbon cables have a characteristic impedance of approximately 110 Ω. Forced perfect (FPT) termination is similar to active termination, but with added diode clamp circuits which absorb any residual voltage overshoot or undershoot.


I suggest to try passive termination first.