Customer asked service of this really nice 10″ reel capable 7.5IPS stereo quarter track reel to reel with a handy reverse-play option!
Back off first – a bit of dust removal to undertake!
Front panel removed for access to mechanicals:
Restored tape counter to aid visibility (black plastic faded):
Some more photos prior to service:
Replaced 4 oxidised/tarnished 2SC458 transistors on preamp board that are prone to failure (the tarnish can creep inside causing them to go noisy)
Testing some music recording after service actions and calibration performed:
White marker added to adjustment screws for any future reference
and started buttoning up front panel prior to refitting head block cover and pitch control knob:
A really lovely unit.
Full list of service actions performed:
Cleaned and polished grabby solenoid slugs affecting pinch roller actuation
Cleaned and lubricated sticky pinch roller actuation mechanism
Removed hardened deposits from pinch roller and capstan
Pinch roller sintered bronze bushing lubricated with Anderol 456
Cleaned and demagnetised heads and tape path
Replaced tired and loose tape counter belt (104mm dia x 1.2mm square)
Lubricated squealing tape counter on fast wind
Cleaned switches and scratchy pots
Repaired stretched/loose memory knob retainers
Stripped down and cleaned pitch control relay causing intermittent record speed performance
Cleaned and checked tension arm guide rollers – loose play gap = 0.1mm – no adjustment needed
Roller block height = 43mm – no adjustment
Reel table height = 15mm and reel takeup centred – no adjustment
Capstan loose play = 0.1mm – no adjustment
Brake lever adjusted to 180 degrees
Braking tension measured at 510g left, 520g right (spec 550 +/- 50)
Brake microswitch repositioned to 0.75mm (0.5 – 0.1mm)
Pinch roller position adjusted to 0.7mm (0.5 – 0.8mm)
Pause plunger adjusted to 0.5mm gap between pinch roller and capstan (0.3 to 0.5mm)
Pinch roller pressure measured at 1.22Kg (spec 1.2Kg +/- 200g)
Calibrated speed (3.75 and 7.5ips) with 1kHz reference tape (was slightly slow but within spec of 0.5%)
Tape guide height ok – no adjustment needed
Head height adjustments:
REV recording head out of position – edge of tape to head core = 0.0mm after adjustment
FWD recording head no adjustment needed
REV/FWD playback heads no adjustment needed
Head alignment:
REV/FWD playback Azimuth adjusted with 10kHz reference tape
REV/FWD playback head angle no adjustment needed
REV/FWD recording azimuth adjusted to match playback
REV/FWD recording head angle no adjustment needed
Level adjustments:
REV/FWD Playback L/R levels adjusted to 0 VU, 0.775V output, 250nWb/m reference flux
L/R Meters adjusted to 0 VU indication
REV/FWD L/R Recording of 1kHz 0.775V signal adjusted to 0VU output on tape*
Frequency response adjustments:
REV/FWD L/R at 3.75ips – 1.5kHz to 8kHz flat response (significant drop off from 12kHz)
REV/FWD L/R at 7.5ips – 1.5kHz to 15kHz flat response
Music test – almost imperceptible difference monitoring between source and recording on tape.
Reassembly and final test – all functions acceptable – ran through entire 10” reel tape twice over.
Other notes:
Preamp model TH-5001A, found previous repairs (replacement transistors)
Slight imbalance in line input (L slightly lower – pot variance)
Slight imbalance in left meter (lower @ idle zero-signal position)
Tested with Maxell UD, frequency response linear at 7.5ips, drop off from 12kHz at 3.75ips
Recalibrated recording level slightly to match supplied tape
*NB tapes of lower quality/differing/older formulas can have significant variation in recording characteristics that cannot be compensated for by the wide-range selector – if a particular tape is to be used exclusively it would be recommended to have the machine recalibrated for the specific tape type.
Also found the NAB reel adapters were difficult to operate – Teflon dry powder lubricated to satisfactory operation, and unit returned to its very happy owner!
