Saturday, May 4, 2024

DMA Core Loader PCB has issues - gambled and lost; intrigued by 360 voltage regulator card I bought

DISCOVERED A FEW ISSUES WITH THE PCB DESIGN ALREADY

I have not completed all the testing yet with breadboards and an 1130 but I have already discovered a couple of flaws. One of the issues would be a huge pain to resolve by cutting traces and adding bodge wires, so I won't bother. I knew the risk when I submitted the first design; just a few dollars wasted. 

I did take the time to optimize placement of the decoupling capacitors, which generally involved relocating quite a few unrelated traces to make room for the capacitor as close as possible to the chips they support. 

I have a new PCB design set up in KiCAD but will hold off sending it to be fabricated until all my testing is done. This adds some schedule delay waiting for the boards after the testing wraps up, but it minimizes the chance that the next set of boards requires any rework. 

EBAY PURCHASE OF 360 REGULATOR CARD MAY BE WORKABLE REPLACEMENT

I purchased a card on Ebay that had the 026 transistors I lacked to repair the VCF 1130, thinking that it was incompatible but a good parts source. The documentation I have for the 1130 shows two versions of the voltage regulator, a 'previous' and a 'new' version. The VCF machine has the previous style. The new style is different enough that the regulator card and the supply can't be mixed with pieces from the previous type.

However, examining the new card shows that it is neither the previous nor the new type. It is however pin compatible with the previous style and may work just fine with the supply. This appears to be a newer design leveraging a later IBM transistor than was available when the previous card was designed.

The previous type used an SMS card that had twin 026 transistors as a comparator, an 086 driving an 028 which then drives the final 108 transistor on the card. The 086 is NPN while all the other transistors are PNP. 

The new type SMS card has twin 026, but they are amplified by a chain of two 183 transistors before driving the 108. One of the 183 has a heat sink pushed on it, thus it is the second stage of amplification. I don't have schematics for the card but will produce one by some reverse engineering. The design appears similar enough to the previous SMS card, other than the change to deploy twin 183, that I suspect I will find the circuitry pretty similar outside of the areas directly driving the 183 parts. 

Previous on left, mystery board on right

No comments:

Post a Comment