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Welcome! You may find this guide from our Resources section helpful: https://tinkerdifferent.com/resources/zero-track-alignment.37/

That's odd as i didn't change the hole sizes for the maceffects board gerbers - must just have been a manufacturing thing with the blue ones!

The location of U1F etc is easily found by looking at the X and Y axis of the board. Along the bottom, numbers. Along the side, letters. Draw an imaginary line to follow the location. So U2C = the IC located where the number 2 intersects with the letter C :) Silkscreen nomenclature is: U =...

I've bought from this seller before - no 7457's left, but there's a few 7455's https://www.ebay.com/itm/392418710733?hash=item5b5dfa54cd:g:wDsAAOSwhA1ddpPA

Here's the schematic of the IIfx startup circuit: Well, my money would be on R3, Q1, C61, C62 or a trace somewhere. Worth checking, anyway :)

I wonder if someone in the 3D Printing subsection might make one of these that's more suitable for the depth of axial electrolytics?

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The pattern on the screen is uninitialised RAM - it's displaying whatever is in the RAM at that moment. I had this issue when trying to bring up the SE Reloaded initially - check the 74LS257's at U1F, U2F and U2G. On the Total Systems Accelerator - the P1 connector pins look a little dull -...

Think yourselves lucky that you got the ZX81 and not the ZX80 - the ZX81 is at least a bit more capable - watch out for the RAM pack installation - you'll ideally need some of this to make it connect well enough to not just fall out the back...

I need to post off those SIMM sockets this week, I'm doing a lot of interviews at the moment which means my ability to go out to the post office is a little hindered.

That's what's known as a hybrid module. Usually a collection of discrete parts, occasionally with some simple logic, on a tiny board, thats then coated with epoxy and turned into a throughhole part. In this instance it could be anything - i cannot find a datasheet for the part.

Ah - that's because the blue version was before i updated the silkscreen - either work, but the MC3488 is NLA and the SN75150 is the modern replacement.

I've found eBay to be a decent supplier of components that are out of stock elsewhere - for things like passive components, there's probably not much difference and half the time is overstock from someone buying off mouser in bulk :)

For the value, yes, that's easy - but getting something that's the correct pinout...that's harder.

If you'd be interested in selling either - i'd be keen to reverse engineer the nubus/pds adapter board.

27.000MHz oscillator - it's the input clock for the Zoran ZR36050 JPEG Encoder chip. There's only two valid input values for the input clock on that chip, 21.000 MHz or 27.000 MHz.

Yes, check the 26LS chips as well - not just the trace continuity but perhaps there's a failure somewhere. Did you check all the GND and VCC connections?

Well people in the US could continue buying from pe-connectors, its just that we need distributors for the international purchasers. Perhaps it might also be worthwhile reaching out to show pe-connectors the market they're impacitng directly...?