Hi, I got an nice JVC RC-90M Boombox with an issue with the cassette transport, when I turn it on, all I hear and see is the solenoid momentary going up and down. Nothing else working when I press Play, ff or rewind, the belts are all fine. Not sure if the capstan motor should be spinning all the time on this? I checked on pin 5 of IC701 when i press play it changes from 5V to 0V, so the play switch is working. Pin 18 = 5V as expected. I noticed on the output pin 14 when play is pressed, the voltage stays around 0.7V (no change when pressed or released) I also checked resistance between pin 4 and 8 / 9 and with cassette out it is 1.4kohm and in 7.55kohm so the micro switch that detects the cassette seems ok I think. I checked all the electrolytic caps and all ESR / capacity measure fine. Checked all diodes, and transistors (removed out of circuit) all seem fine. Fr702 =1425ohms, Fr703 = 4.47ohms, fr701= 5.31ohms, (need to confirm these are correct) I also temporarily disconnected pin 11 (power off reset) from the chip, but no change. Could this be a faulty (JVC VUC0002) IC701 chip? Any other suggestions what to check ? I see the photo diode led on. Hoping someone has had the same issue and that there might be a common "known fault" with these transports
Attachments
These are the voltages relative to ground on IC701, with cassette inside.
Pin1= Confirmed connected to ground with continuity meter.
Pin2=5.22
pin3=5.23
pin4=5.23
pin5=5.23
pin6=0.02
pin7=0.02
pin9=5.23
pin10=0.70
pin11=5.26
pin12=0.02
pin13=0.02
pin14=0.02
pin15=1.8
pin16=3.76
pin17=0.01
pin18=5.28
Anyone experience with these ? Thanks in advance.
Pin1= Confirmed connected to ground with continuity meter.
Pin2=5.22
pin3=5.23
pin4=5.23
pin5=5.23
pin6=0.02
pin7=0.02
pin9=5.23
pin10=0.70
pin11=5.26
pin12=0.02
pin13=0.02
pin14=0.02
pin15=1.8
pin16=3.76
pin17=0.01
pin18=5.28
Anyone experience with these ? Thanks in advance.
Also when I hit the record and play button the rec led comes on, but nothing else, head does not rise, just the solenoid turns on on power up
One more observation today, when measuring the DC input on the capstan motor I have 12.3V on both the orange and white wires, when I remove both wires, relative to ground I measure red=12.3V and white 1.6V, but when connected again both meaure 12.3V, i tested the motor with external 12V DC and it spins fine, when I activate the solenoid the head goes up as expected.
I am beginning to think it is my jvc VUC0002 IC701 as The input voltage to the chip changes when I press the corresponding controls, but the output does not change, unless one of the logic protection circuits is preventing it, there are 4 X m74ls005 logic gates with!! a fairly complicated circuit. These are available and might just order 4, the VUC0002 is as rare as a hen's tooth
pins 6 & 7 are both low. I don’t think FWD and REV should be engaged at the same time.
Look at usual suspects like oxidized switches. Blame the ICs later.
Look at usual suspects like oxidized switches. Blame the ICs later.