I find the cluing of these puzzles just slightly unconventional. Bit tricky, but fair and fun!

Across

1

Co-ordinate scheme that defines breadth and display of information (6,5)
NOTICE BOARD — anagram of CO-ORDINATE with B (breadth)

7

Half size up halfwit (3)
ASS — half of ASSESS (size up)

9

Transfixed by flipping bonkers bottom (7)
STABBED — reversal (flipping) of BATS (bonkers), then BED (bottom)

10

We turned in writing, say, and mechanical learning put it in other words (7)
REWROTE — reversal (turned) of WE between R (writing, one of the "three Rs") and ROTE (mechanical learning)

11

Love's turn to hold up flower (5)
LUPIN — reversal (turn) of NIL (love) to hold UP

12

Drive over ha-ha in street (9)
ONSLAUGHT — ON (over) LAUGH (ha-ha) in ST (street)

14

Twit seen dancing in time with the flappers? (8)
TWENTIES — anagram of TWIT SEEN

15

Child carried the can as right as a trivet (4-2)
SPOT-ON — POT (can) inside SON (child)

17

Thought sane or insane? (6)
REASON — anagram of SANE OR

19

Colt sire's unsuited to the monastic life (8)
CLOISTER — anagram of COLT SIRE

22

Hungriest beast's dead certainty (4,5)
SURE THING — anagram of HUNGRIEST

23

Ranks from Helvetia raised to protect the papacy (5)
TIARA — hidden in helveTIA RAised

25

Tavern seen and heard to have egged on (7)
INCITED — homophone of INN SIGHTED (tavern seen)

27

Finished with secular design on top (7)
OVERLAY — OVER (finished) and LAY (secular)

28

Clear out towboat from the stern (3)
GUT — reversal of TUG (towboat)

29

Salute superior donation with heraldry (7,4)
PRESENT ARMS — PRESENT (donation) and ARMS (heraldry)

Down

1

Banana's almost hidden in the nose (5)
NASAL — hidden in banaNAS ALmost

2

Raise design on mince pies or go heavily without design (7)
TRAIPSE — reversal of ART (design) on anagram of PIES

3

US secretary's position on secretaire letters (7,4)
CABINET POST — CABINET (secretaire) and POST (letters)

4

Spooner had voiced drag's risk of invalidity (8)
BEDSORES — Spoonerism of SAID BORES

5

Fears throwing husband over again (6)
AFRESH — anagram of FEARS, H (husband)

6

Owing, some say, to nocturnal dampness (3)
DEW — homophone of DUE (owing)

7

Army doctor gripped by dread in the thick of things (7)
AMONGST — MO (army doctor) inside ANGST (dread)

8

Bribe Frenchman who came up after lolly (9)
SWEETENER — reversal (came up) of RENE (Frenchman) after SWEET (lolly)

13

Date mobile program scribbled on mitten (11)
APPOINTMENT — APP (mobile program) and anagram of ON MITTEN

14

Oxidation filling object full of energy (9)
THRUSTING — RUST (oxidation) inside THING (object)

16

Waste huge poll figures (8)
PLUGHOLE — anagram of HUGE POLL

18

Month one laid on bed, pretty yellow (7)
APRICOT — APR (month) I (one) on COT (bed)

20

Left in freshwater on right fishing boat (7)
TRAWLER — L (left) inside anagram of WATER on R (right)

21

Drilled rocks outside core to make a lot of holes in it (6)
RIDDLE — anagram of DRIlLED (without the middle/core)

24

7-across subsumed by chaos (5)
ABYSS — ASS (7-across) with BY inside

26

Dump inside information (3)
TIP — double def.