ITT 8025 Cassette Deck
Cassette Transport
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| Rightmost is the back tension brake and 'new' felt pad. |
Drive Belt: Out of sight is a 79mm x 5mm flat belt for the motor and two flywheels.
Lapped Record Head
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| Original Playback Head Lapped |
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| Some New E-clips |
Observe that the record head is aligned slightly to the left, although it does not catch any cassette shell to date.
With record head removed.
Head plate, was later partially reamed to allow a slightly further drop or effective reduction in head penetration during PLAY.
Three bolts hold the returned head plate. The threads for the bolts are located underneath the head plate. The effective drop in head penetration during PLAY is now approximately 0.5mm less than previous.
All heads returned and re-aligned using a M-300 gauge (for tilt), a Hans Peter Roth 'narrow track' 1Khz head height tape, and an ABEX 10Khz full track reference were used for playback head alignment.
However, there was another yet-to-be-fixed issue. And that was - the record head was still too far left-of-centre, so the whole process was repeated above, but this time extra reaming to allow the plate to be shift a little more to the left.
Recording Failure
My assumption of a faulty HA1457 later turned out to be incorrect, however that didn't stop me from removing the old HA1457 ICs and replacing them with a TL071 OP Amp based solution with step-down voltage 1N4148 diodes in series.
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| Original HA 1457 Pre-emphasis Amplifier |
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| HA 1457 Replaced with a TL071 Circuit Solution |
It wasn't until I had ran the unit with the new pre-emphasis pre-amps that I realized the fault may have been caused by a faulty Dolby integrated circuit, namely the LM-1011 in the recording chain.
After interrogating input pins 5 and output pins 7 on each LM-1011, the right channel had clearly failed at the output on pin 7. Both ICs were carefully removed, and with new 16 pin DIL sockets in exchange, I was tempted to try the Signetics NE545B Dolby chip.
After consulting the datasheets on the NE545B series, I was partially confident these would work.
The supply voltage to the previous LM-1011 was 20v (exact), and the maximum rating of the NE545B is '24v' or is it 20v? So, just be to be 'on the safe side', I wired into the supply rail a single 1N4148 signal diode to drop the voltage by about 0.7v. This was done by cutting the track on the solder side of the board and positioning just one 1N4148 signal diode.
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| Two Dual In Line ('DIL') Sockets host the NE545B Dolby ICs. |
Both left and right channels are now recording, and playing back well.
{More on this may follow}
Tape Transport and Tape-Slowing
Playing some cassette shells still resulted in the tape slowing down, which I initially thought was due to the record head being too left-sided, and overall head penetration too excessive?
Well, the above were indeed issues to be corrected if possible, but the nagging issue of some cassette tapes and their shells causing mischief for unrestricted transportation still proved a stumbling point.
That is, until I notice something in an earlier image I took of the deck. It became apparent that there was a conflict between the supply tape guide and the cassette shell - the two sides were making contact on some cassette shells, most noticeably on an old 1970s AGFA, and 1990s TDK D46.
I realized much earlier that manually lifting the cassette shell during PLAY resolved the issue, but I was still certain that the left-leaning record head and general head penetration were solely to blame.
As a final attempt, I decided to check out the supply tape guide, its positioning and the baseline on which the shell sits. After loosening the baseline guides, I realized that these had probably slipped downwards over the years through casual insertions of the tapes. And so it proved to be, by resetting the baseline height the whole transport became fully cooperative!
No more tape dragging!
Tape Creasing:
How much the tape dragging problem concealed tape creasing I'll never know, but the machine does crease tape on some cassette shells - it seems to begin on the supply side.
The old supply pinch roller measured 9mm x 8mm x 1.5mm, but I only had a single 9mm x 7mm x 1.5mm in stock. This new roller worked, but 'end play' had to be reduced. End-play was reduced with suitable nylon washers.
However the new roller did not eliminate any tape creasing.
Tape creasing is sometimes caused by ...
(1) the tape being fed into the supply capstan/pinch side which is slightly uneven - either due to ineffective back tension, a poor cassette shell, or an out-of-parallel capstan/pinch roller line.
(2) on some occasions concurrently, it can also be invoked by insufficient supply capstan/pinch pressure, as the take-up side is perpetually pulling the tape along - the tape also 'micro' slips here?
(3) Head tilt which is not 90° to the plane of the traveling tape. There is obviously a margin of error here which would be acceptable.
For this ITT 8025, increasing back tension will stop tape creasing, but on this machine back tension was (I believe) sufficient. Increasing capstan to pinch roller pressure also cured this problem, and to achieve this I had to configure the tension springs into a slightly more tensile state.
I first swapped the springs - I may have made a mistake earlier by swapping the, I cannot remember?
Secondly, the tension of each tension spring was increased a little more by placing a plastic sheath over the anchor point in each case as illustrated below.
Finally, the playback head tilt was checked again and altered very slightly to favour an even tape wrap across the head. An M-300 gauge is essential.
Tape creasing tests were performed on cassettes without a tape pad.
{Possibly more to follow}
14/04/2026
