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Old 23rd Apr 2019, 9:31 pm   #70
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: MK14 programming interface - MK2

The following is a direct copy of the component list which came with my issue II MK14. Where the components actually fitted are different from the parts on the parts list, I have stated the part actually fitted.

All of the components in this list, save one, are the original Science Of Cambridge kit supplied parts. It is probably fatal to say this, but the machine has always worked, so I have never had to replace any parts.

The one non-original exception was the INS8154 - that was bought from Tandy shortly after I got the MK14, but it is an original Nat Semi part.

The crystal is in with the 'miscellaneous', mainly hardware parts, which I have not included in the list - it was originally a large-can 4.43MHz TV colour crystal, was replaced for a while with a small-can 4.00MHz crystal (the VDU period) and then reverted back to a large-can 4.43Mhz crystal when I started to return the machine to something more like its original condition.

Code:
IC1	ISP-8A / 600 (SC/MP)
IC2	DM74S571
IC3	DM74S571
IC4	MM 2111-1N	Actual component fitted: uPD2111AL-4 (NEC)
IC5	MM 2111-1N	Actual component fitted: uPD2111AL-4 (NEC)
IC6	MM 2111-1N	Actual component fitted: uPD2111AL-4 (NEC)
IC7	MM 2111-1N	Actual component fitted: uPD2111AL-4 (NEC)
IC8	INS8154N
IC9	DM74LS157	Actual component fitted: SN74LS157N (Texas Instruments)
IC10	DM74LS157	Actual component fitted: SN74LS157N (Texas Instruments)
IC11	DM 80L95
IC12	DM 74LS173
IC13	DM 7445
IC14	DM 7408
IC15	DM 7408
IC16	DM 74LS08
IC17	DM 74LS00	Actual component fitted: SN74LS00N (Texas Instruments)
IC18	DM DM74LS04
IC19	LM340T-5.0

Resistors

R1	4K7
R2	2K4
R3	100K	Actual component fitted: 150K
R4	1K2
R5	2K4
R6	1K2
R7-R10	1K2	'May be any value between 1K and 15K'. Actual values: All 4K7
R11	4K7
R12-R15	1K2	'May be any value between 1K and 15K'. Actual values: All 6K8

Capacitors

C1	27p for 33p (sic). Actual value: 33pf
C2	1000uF 40V
C3	0.01uF
C4	0.01uF
(There is no C5 either on the list or fitted)
C6	22uF 16V
As to the curious disparity between R7-R10 and R12-R15, all listed as nominally 1K2 but two different larger values on the machine - the 6K8 resistors are physically smaller than the rest - 1/8th watt size - and so I must have chosen to use those as R12-R15 which are the only resistors mounted vertically on the PCB, between IC2 and the PCB edge. Incidentally my original layout diagram shows those resistors as R11-R14 but the PCB screen printing shows them correctly as R12-R15. The 4K7 reset resistor is shown as R11 both on the layout and on the PCB screen print.

I grabbed 5 of those genuine ex-RS SN74LS365 ICs to try in my MK14 in the IC11 position - I'll try that later in the week.

Last edited by SiriusHardware; 23rd Apr 2019 at 9:44 pm.
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