Sharp VZ Microcomputers

Wondering if there is any ability to swap out the microcomputer (IC501) between models? Obviously there are no readily available replacements.

VZ2500 - IX1230AFZZ
VZ2000 - IX1220AFZZ

I don't think they are compatible but wondered if someone had looked into this before to determine if they would work in each other?
Just a thought.

No

Still having difficulty identifying the variable warbling occurring on the turntable.
I have replaced Q501-Q510, all capacitors also.
Another thing I tried was replacing the IC which controls the phono motor IC505, the 10k VR's and tested the resistors around Q508c which all check out.

One of the symptoms I have noticed is that the VR for 33RPM does affect speed while the VR for 45RPM pretty much does nothing even after replacing them both.
I'm thinking the microcomputer could be shot?

Anyone have one going spare please?

Dave what does the part look like , I still have turntable parts left.

Its the largest IC on the board, like 42 pins i think.

Please let me know Floyd, cheers.

I'm curious why you think the entire CPU is dead simply because it's not detecting play speed properly? There could be a number of reasons for that

Other than the phono motor control IC, q508, vr’s and a few resistors, I’m not sure what else to try.

Hmm. Have you checked the level of that pin on the CPU to see if it's low for 33RPM and high for 45?

I have not yet as I assume this will require the use of an oscilloscope which I do not know how to use?
I do have one so could see if I can suss it.

It's not a pulse, you should be able to read something close to 0V for 33RPM, and probably something like 5V for 45RPM.

Ah ok my bad Eric.
Hmm tested this and switched between 33/45 and voltage on pin 39 remains high at 4.8v.

Hmm. You might want to disconnect that pin so it's isolated when you measure it, to make sure nothing tied to it it forcing it high all the time.

Seems to be the same condition with pin desoldered. Tested continuity with pin and pad to be sure it is disconnected but still has 4.8v anx remains while switching between speeds.

Do you have issues with anything else, or is it just 33/45?

I don't think so, it plays both sides separately, plays/cuts/cues, both side play etc. Only issue is “warbly” output on either speed, though the VR does affect 33 but the other VR doesn’t work on 45 as it should.

I’m not 100% certain as I only use 12” records of both speeds but I’m not sure it should detect speed between 33 and 45 12” records. I think this is normal to select the right speed.

OK. I was just asking because if you knew you were having issues with any other buttons, it could be a problem with the button connections. The 33/45 button is part of a 3x3 matrix of buttons, with the three column and three row wires tying into the CPU on pins 2-4 and 27-29. If anything was wrong with the row or column wire going to the 33/45 button, that would prevent the CPU from getting the signal that it should change speeds.

I see, I will double check pressing all buttons.

Checked them all and all action buttons work while the repeat/replay buttons light up the lights on the front.

caution said:

OK. I was just asking because if you knew you were having issues with any other buttons, it could be a problem with the button connections. The 33/45 button is part of a 3x3 matrix of buttons, with the three column and three row wires tying into the CPU on pins 2-4 and 27-29. If anything was wrong with the row or column wire going to the 33/45 button, that would prevent the CPU from getting the signal that it should change speeds.

Click to expand...

Are we talking about the VZ2000 here? Like Caution says, there's so many things that affect operation, it's not so simple to just blame on MPU, which is merely a processor. Think, garbage-in = garbage-out. If it's not getting the proper signal to tell it to switch from 33/45, then maybe it's just responding to what it thinks it should be so you need to make sure it knows it's supposed to be on 45. If I'm not mistaken, there is no indicator that tells which speed it's on. Also, the VZ-2000 has a built in EP/LP sensor so if you are are playing 12" records only, then it's default would be to play at 33rpm right? As for the warbling... speed is not a function of the MPU, which merely sets 33/45. It does not control speed. The phono motor itself, however, has an internal voltage generator which plays an integral part of the speed control circuit as it affects base voltage of those transistors. If that internal voltage generator is not outputting a stable voltage, you won't get stable speed. You might see if cleaning that motor helps, just something to think about in case it's having an affect on your symptoms. Just wanted to throw in that this isn't a simple motor. The VZ-2000 is perhaps one of the most complex boomboxes we have.

Hi Norm, this is the vz2500. I have changed the motor for another vz2500 motor as I thought that or simply the belt was the issue but couldnt adjust the 45 speed via the VR.

I completely get what your are saying.
Having replaced all caps and transistors, checked a bunch of voltages, I’m at a loss.