18.02.2021, 12:55
Servus Peter,
vielen Dank für deine Antwort. Es ist tatsächlich so, dass die Maschine langsamer wird und bis zum Stop kommt, wenn die aufwickelnde Spule zu 85-90% voll ist. Schaltplan und Servicemanual habe ich bereits im Netz gefunden (nur werde ich daraus nicht recht schlau), leider habe ich aber auch eine Webseite gefunden, die genau dieses Problem schildert (siehe unten). Das passt auch gut ins Bild, das GXNet Michael oben zeichnet.
Eben teste ich ein Maxell Band. Vorwärts gestoppt bei ca 85% Restband, rückwärts lief sie durch bis zum Ende - es ist zum Wimmern. Ich werde mal weiter mit dem Maschinchen spielen, vielleicht finde ich ja noch einen weiteren Hinweis, der mich positiver stimmt.
Für Hilfen in jede Richtung bin ich weiterhin extrem dankbar.
Viele Grüße
Rainer
===
Von https://reeltoreeltech.com/akai-reel-to-reel-summary:
Underrated capstan motor. This is the big one, since it’s a servo motor unique to the GX-77. The transport uses a dual capstan shaft design, with one really long belt between the capstan motor and the flywheels. We’ve had in many GX-77s in the last few years that would play one side of the tape just fine, then the deck would slow down over about a 5 minute period, and stop completely. Let the deck cool down, and the cycle would repeat.
After many hours of playing with a number of these defective decks, we’ve come up with the following theory as to why the motor fails. We noted that the time it would take the capstan flywheels and motor to stop spinning at power-down ranged anywhere from 4 seconds for a problematic deck, to about 6-7 seconds on a deck that worked. We therefore tore down the entire transport, and cleaned and lubricated the capstan flywheel sleeve bearings, and usually noticed a decrease in friction of the flywheels, putting less of a load on the capstan motor.
The capstan motor also has a thermistor in line with the motor supply voltage, preventing burnout of the motor if it gets jammed. Our theory however is that as the friction of the capstan flywheels increases over time, the motor is subjected to a slowly increasing load, which eventually causes shorted motor windings. The shorted motor windings draw more current as the motor gets warm, causing the thermistor to heat up and limit the current going to the motor, resulting in motor slowdown and the eventual stopping of it. Turn the deck off for ½ hour, the motor cools off, the thermistor cools down, and the deck works fine again.
Since the capstan motor is a servo unit with a controller PC board, it’s unique to the GX-77 and no other motor will fit. If you’re lucky and can find a used motor on eBay, they appear to be selling for about $100. Given all of the other problems with the GX-77, we caution you not to put a lot of money into this problematic, over-engineered deck.
vielen Dank für deine Antwort. Es ist tatsächlich so, dass die Maschine langsamer wird und bis zum Stop kommt, wenn die aufwickelnde Spule zu 85-90% voll ist. Schaltplan und Servicemanual habe ich bereits im Netz gefunden (nur werde ich daraus nicht recht schlau), leider habe ich aber auch eine Webseite gefunden, die genau dieses Problem schildert (siehe unten). Das passt auch gut ins Bild, das GXNet Michael oben zeichnet.
Eben teste ich ein Maxell Band. Vorwärts gestoppt bei ca 85% Restband, rückwärts lief sie durch bis zum Ende - es ist zum Wimmern. Ich werde mal weiter mit dem Maschinchen spielen, vielleicht finde ich ja noch einen weiteren Hinweis, der mich positiver stimmt.
Für Hilfen in jede Richtung bin ich weiterhin extrem dankbar.
Viele Grüße
Rainer
===
Von https://reeltoreeltech.com/akai-reel-to-reel-summary:
Underrated capstan motor. This is the big one, since it’s a servo motor unique to the GX-77. The transport uses a dual capstan shaft design, with one really long belt between the capstan motor and the flywheels. We’ve had in many GX-77s in the last few years that would play one side of the tape just fine, then the deck would slow down over about a 5 minute period, and stop completely. Let the deck cool down, and the cycle would repeat.
After many hours of playing with a number of these defective decks, we’ve come up with the following theory as to why the motor fails. We noted that the time it would take the capstan flywheels and motor to stop spinning at power-down ranged anywhere from 4 seconds for a problematic deck, to about 6-7 seconds on a deck that worked. We therefore tore down the entire transport, and cleaned and lubricated the capstan flywheel sleeve bearings, and usually noticed a decrease in friction of the flywheels, putting less of a load on the capstan motor.
The capstan motor also has a thermistor in line with the motor supply voltage, preventing burnout of the motor if it gets jammed. Our theory however is that as the friction of the capstan flywheels increases over time, the motor is subjected to a slowly increasing load, which eventually causes shorted motor windings. The shorted motor windings draw more current as the motor gets warm, causing the thermistor to heat up and limit the current going to the motor, resulting in motor slowdown and the eventual stopping of it. Turn the deck off for ½ hour, the motor cools off, the thermistor cools down, and the deck works fine again.
Since the capstan motor is a servo unit with a controller PC board, it’s unique to the GX-77 and no other motor will fit. If you’re lucky and can find a used motor on eBay, they appear to be selling for about $100. Given all of the other problems with the GX-77, we caution you not to put a lot of money into this problematic, over-engineered deck.
In Betrieb: AKAI GX-77, AKAI GX-630, AKAI GX-625, Pioneer RT-707, Revox B77 MKII 2 Kanal, Revox B750, Revox B780
Auf der Werkbank: Revox B77 4 Kanal
Leider viel zu wenig Zeit für dieses tolle Hobby
Auf der Werkbank: Revox B77 4 Kanal
Leider viel zu wenig Zeit für dieses tolle Hobby