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  #1  
Old 10-16-2017, 08:20 PM
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1000ZXL – Poor IC Replacement & Additional Jumper Wires!!!

Hi All,

As I am rebuilding my 1000ZXL I have come across an IC that been replaced on the CPU ‘B’ PCB (IC 802 – uPD4508BC), the IC was originally a NEC IC and has been replaced with a Toshiba TC4508BP. I cannot find a spec sheet for the NEC uPD4508BC but have read information that suggests that the Toshiba TC4508BP is a suitable replacement.

I have attached a couple of photos showing the pin side of the IC and as can be seen it was very poorly installed with copper traces damaged and jumper wires fitted. Of note is there is a jumper wire going from Pin No. 13 (master reset) to the CPU ‘A’ PCB, CP4, that in turn has wire that goes back to the power supply PC4 (Initial Reset) output. The jumper between CPU ‘A’ & ‘B’ appears to have been added, as it is not on the original schematics and the black wire matches the other jumper wires that have been added to overcome the damaged copper traces.

My question is, why has this been done? Can the wire be removed?

I intend to remove the IC and fit a socket replace the jumper with solid (0.5mm) silver wire. This should tidy things up, but I am puzzled about the jumper wire between the two boards.

Any thoughts on this would be appreciated.

Tony
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File Type: jpg IMG_9261 (Large).jpg (124.1 KB, 107 views)
  #2  
Old 10-16-2017, 11:31 PM
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Hey Tony. The two ZXL's I have here have that same jumper wire between the two CPU boards.

Just to update you on my progress, I discovered that the power up and have to reset the machine every time glitch only happens when the CPU boards are down in their normal position. When they are in the up position it powers up normally. I discovered that while the boards were up looking for any obvious problems. So obviously it is a poor connection somewhere. I haven't located it exactly yet and fixed it but just the fact that I discovered it made my day.

I also finished my test box but it has not been tested yet. I had to shelve the deck again to work on other priorities.
  #3  
Old 10-17-2017, 04:07 PM
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When a soldering iron is too hot the foil separates from the board. Those jumper wires are the correct repair method. If you want to trim them shorter do so, but I wouldn't stress over it. The part substitution is fine too.
  #4  
Old 10-17-2017, 07:16 PM
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Hi All,

Thank you for your response Nakmandan & Nakdoc, very much appreciated.

Nakmandan, can I ask you what colour the wire is between the two boards?

I have also built the test box, so I would be interested in how you intend to test the box prior to using it, are you able to advise?

I have one known remaining fault (intermittent) with my 1000ZXL and its when recording the signal is very distorted in both channels, I have traced the fault to the Record Eq. Amp. PCB. I note the four wires that feed into that board from the CPU ‘B’ PCB (CN-52) are connected to this IC 802, so I am keen to check this out and test it to make sure all is good, then via my extension leads remove and check the Eq. Amp. PCB itself.

Tony
  #5  
Old 10-17-2017, 11:33 PM
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The jumper wire on both machines are black.

I guess I am just going to plug in the box and see how it works. I was very careful while building it to follow the schematic with Willy's extra switches added, running all the wires and pins to the connectors so I am confident it will work.

Without doing anything with the test box yet, I have observed that calibration takes about 42 seconds with just about any tape. A Type I tape does pretty well with frequency response after calibration but a Type IV is always a couple of dB off from source across the board. Hopefully tuning the machine with the test box will fix that. But I want to get the last few quirks fixed before doing the final tuning. The only ones left are some minor ones: Using the timer switch in record will put the deck into play, using the switch in play, nothing happens, it just turns on like normal. Another problem is the the counter memory stop will stop at 0000 but it will not go into play from counter memory play, it just zooms right on by 0000 and keeps going. And the last problem is the mute when powering down, or lack thereof. When the power is turned off, I get a huge thump/screech just before it powers down from both the headphone and line out jacks.

The second deck has been shelved for a while when I got shut down by the inability to get the cam indexing sorted out. I actually was able to get the indexes correct by changing the resistors as it states in the second part of the indexing procedure but once I got that sorted, it would no longer go into record! Haven't got that deck out since but need to get back to it. I suspect some issue with the voltage comparator IC since I have checked everything else and compared it with the working machine and there is nothing else left that could be wrong in the circuit but the chip.
  #6  
Old 10-18-2017, 04:53 PM
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Thanks Nakmandan for the info, very interesting, I hear you regarding finding faults on these machines, it really does make your day when you find a problem and fix it.

I like you have carefully built the test unit ensuring all the many connections are correct. I found using 10 different coloured wires helped. Regarding the modification to the Reset Circuits, did you make any change to the RAMM Reset circuit as shown on the schematic? I would have thought that this would have required the same modification as shown on Willy’s CPU & RAM Reset mods?

I also am trying to fix all the known faults before attempting a full set of calibration checks. I have made some calibration checks and adjustments along the way, in an attempt to get things working correctly.

Tony
  #7  
Old 10-18-2017, 08:52 PM
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Hi Nakmandan, I have been checking IC 802 circuits today and notice that the jumper (J018) between IC 802 pins 12 & 13 has been cut, referring to the photo it appears the link was in place and has been cut to break the circuit. This make some sense as pin 12 goes to ground and I couldn’t work out why any reset voltage would just go straight to ground.

Nakmandan are you able to confirm that you link has also been removed?

Tony
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Last edited by flaxmill19; 10-19-2017 at 02:24 AM.
  #8  
Old 10-18-2017, 11:01 PM
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Hey Tony.

For the test box, I followed Willy's modified schematic exactly, no deviations.

On the jumper issue, both machines I have here have no jumper at all installed, nothing to cut because it isn't there.
  #9  
Old 10-19-2017, 04:53 PM
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Hi Nakmandan,

Thanks again for your response, it seems that was a modification carried out after the 3rd version CPU ‘B’PCB. I notice that IC 101 & IC 201 (that are both uPD4508BC) on the same PCB have the same jumper and it’s still in place. Do your two have the jumpers on the two above IC’s?

As my 1000ZXL appears to be running OK, I shall tidy up IC 802 and move on to the record issue on the Record Eq. Amp. PCB.

I have been talking with the previous owner (the only one), and he talks about the deck having problems early on and he believes the deck went back to Japan for repair, so maybe that’s when the change was made, but that’s hard to believe as the workmanship is so poor, not what you would expect out of Japan in the mid 80’s!

Thanks, Nakmandan for your help and update on your two 1000ZXL’s.

Tony
  #10  
Old 11-02-2017, 02:15 PM
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https://i.imgur.com/Wi55VXo.jpg

Same damaged copper traces around IC802 on my ZXL but with the original NEC ic in place... The jumper wire is not cut, but its trace is.

Quote:
Do your two have the jumpers on the two above IC’s?
yes

Last edited by Matcs; 11-02-2017 at 02:43 PM.
  #11  
Old 11-02-2017, 03:11 PM
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Hi Matcs,

Thanks for your photo, adds more to the story, I notice your black wire coming from the CPU ‘A’ PCB has been soldered to pin #15, whereas mine is pin #13, these two pins are linked by a trace, so no problems there, it indicates to me that this was not a standard upgrade done by Nakamichi.

You also mention that link J018 is not cut, but the trace is, if the trace is cut between pin #13 and the bottom (as shown on your picture) of where the link solders to the board, that would also cut the trace to pins #1 & #3, seems very strange to me, I assume that your 1000ZXL is working OK?

I am also intrigued to the capacitor (I think), resistors, brown and blue wires at the top (as shown in your picture) what they do? I do not have this modification on my 1000ZXL.

I have replaced the two black wires to CN-52, completely removed J018 on my 1000ZXL and it appears to be working fine.

Tony

Last edited by flaxmill19; 11-02-2017 at 08:41 PM.
  #12  
Old 11-02-2017, 06:08 PM
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Hello Tony,

Quote:
Thanks for your photo, adds more to the story, I notice your black wire coming from the CPU ‘A’ PCB has been soldered to pin #11, whereas mine is pin #13, these two pins are linked by a trace, so no problems there, it indicates to me that this was not a standard upgrade done by Nakamichi.
Actually, on mine it is pin 15 of IC802 that have the black wire connected to CPU A pcb on CP4 point. (as you said it is linked to IC802 pin 13).

I can't post better photos now.


Quote:
You also mention that link J018 is not cut, but the trace is, if the trace is cut between pin #13 and the bottom (as shown on your picture) of where the link solders to the board, that would also cut the trace to pins #1 & #3, seems very strange to me, I assume that your 1000ZXL is working OK?
here is exactly how the trace is cut


I decided to work on my dormant 1000ZXL yesterday only. I have it since 2010. The playback is magnificient.

The unit developped intermitent troubles with time as disapearing FL meter, FL left level higher by 2.5 dB on vu/peak mode, disapearing 400 Hz. More time, and the right chanel wasn't recorded. And as this happened, auto azimuth was impossible as autocal of course. The deck wasn't used anymore an selled to me.

Yesterday, I opened it, and had a major part of the day to carefully remove oxidation on the main bord board vertical connectors. Visually inspect every solder and re-do the bad ones.

Solved:
  • Right chanel is recording again.
  • Left FL meter is OK on vu/peak.

so I was able to conduct the auto cal, and the result is problematic.

First time autocal recording:
  • Auto-azimuth ok. Good quality of the waveform.
  • Max Level Bias adjust: OK
  • EQ: dirty tones (unstable, distorted stained by stepper amp noise), only on right chanel. The left chanel iterations are burst of noise without discernable tones.
    Level was not calibrated, but at the end of this sad calibration, all the lamps where steady. no error judged.

Second time auto cal recording
  • Auto azimuth on the same shell, no adjustment. Good 400Hz waveform.
  • BLE: this time, the other tones than 400 Hz won't work. 400Hz is distorted.
  • The alternating left/right test by level are conducted, but with 400Hz in the EQ sequence instead of the higer tones no more generated.
  • Concluded by Error alarm.

    Recording in normal mode : distorted or sometimes muted

    Silent recording : background popcorn noise



Time has come to plug the oscilloscope.

SO:

The Auto Azimuth and Bias calibration sequence are ok.
Why did the tones are distorted during EQ steps? Because there is no bias oscillated feed to the rec heads during this phase!

Bias 105 kHz is active on Auto Azimuth and BIAS cal.
But not after.

Bias 52.5 kHz for erase head have no problems.

Here is where I am on my day two with it's intimacy.

I am finishing my day with the simple stuff, as the logic pcb connectors & solder inspection.


Quote:
I am also intrigued to the capacitor (I think), resistors, brown and blue wires at the top (as shown in your picture) what they do? I do not have this modification on my 1000ZXL.
My unit is sn° 4197, what's your's ?
I will post a detailed view of the piggy stuff later as you are interested.

Quote:
I have replaced the two black wires to CN-52, completely removed J018 on my 1000ZXL and it appears to be working fine.
Nice to hear... as in officially repaired ?

Matyas

Last edited by Matcs; 11-03-2017 at 05:27 AM.
  #13  
Old 11-02-2017, 09:35 PM
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Hi Matyas

Quote:
Actually, on mine it is pin 15 of IC802 that have the black wire connected to CPU A pcb on CP4 point. (as you said it is linked to IC802 pin 13).
You are correct, it is pin #15. My black wire is also connected to CPU ‘A’ PCB – CP4.
Quote:
here is exactly how the trace is cut
Yes, this is where I thought it was cut, it would be interesting to see if you have a circuit between Pin #13 & Pin #1 or #3?
Quote:
My unit is sn° 4197, what's your's ?
I will post a detailed view of the piggy stuff later as you are interested.
My Serial #3017
I would be interested in more detail around the “piggy stuff” would be great.
Quote:
Nice to hear... as in officially repaired ?
Note quite sure what you mean by officially repaired, but the only real problem I have at the moment is that the RAMM is not working properly. But my intentions are to a full calibration on the 1000ZXL and then see where I am at with the RAMM.

If you wish to read a little more about my 1000ZXL restoration refer http://www.tapeheads.net/showthread.php?t=51271

Tony
  #14  
Old 11-02-2017, 11:44 PM
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I'll just throw in my progress here to catch up. I have been working on the second machine the last couple of days and I have solved three of the last four problems.

The primary concern was that whenever the machine was powered up, the CPU needed to be reset by pressing one of the memory buttons, or nothing else worked. Then I discovered that if I raised the CPU boards in the up position, as if you were inside doing maintenance, it would start up normally. So obviously a poor connection somewhere. After some very tedious visual inspection and then point to point continuity checks while moving the CPU boards open and closed, I discovered one wire had broken inside the insulation. I'm amazed I found it at all. A solid core wire (so it can be wire wrapped) had snapped right in the middle of the run, with the insulation completely undamaged and seemingly untouched.

Another problem was that the memory switch only worked halfway. When set to stop, when 0000 was reached on the counter from fast wind, it worked fine and would go to stop mode. But when the memory switch was set to play, it would just zoom on by 0000 and keep going. This turned out to be tiny micro cuts across the traces from the memory switch. In all honesty, it appears like the silkscreen printing actually cut the traces, because that's exactly where the breaks were. I've never seen anything like that before.

The third problem was with the timer switch. When set to play and the power was turned on, nothing happened, it just powered up normally and assumed stop mode. When the switch was set to record and the power switch was depressed, it would go into play only, but not record. I know what you're thinking- record protect switch! But no. The record protect switch works fine because the machine records normally, it just won't do it from the timer. Well this turned out to be broken solder pads at the timer switch. Visually they looked fine. I even touched up the solder joints at one point, with the same result. It was only when I decided to completely resolder the whole connection did I realize what had happened. I used my vacuum desoldering station to remove the old solder and the whole pad came up off the board with the vacuum! A-HA! The smoking gun! I installed some jumpers from point to point and now the timer works flawlessly.

So the last remaining problem I have yet to solve is with the mute circuit. When the machine is powered off, there is a huge, screeching thump in both the headphone jack and line out. If you have headphones on or an amp and speakers connected when you power off, you will get blasted. For some reason, the mute transistors that are supposed to pull the output signal to ground is not working. My next step is to pull those transistors for test. It wouldn't be the first time I have seen bad muting transistors. Seen it in a couple of LX-5's as well as others.

That is the last known problem with this deck so far. Tomorrow I will connect the calibration box to it and start the calibration process. Wish me luck!
  #15  
Old 11-03-2017, 03:21 PM
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Thanks for the update Dan,

You like me are getting through all the issues you had. I will be very interested to see how you go through the calibration process, hope it all goes to plan and good luck.

Does either of your two 1000ZXL's have the modification ("piggy stuff") to the CPU 'B' PCB as shown on Matyas's board below?

Tony

Last edited by flaxmill19; 11-03-2017 at 03:30 PM.
  #16  
Old 11-03-2017, 04:49 PM
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Dan, replace all the 2SC2785 muting transistors.

Matcs:
The erase oscillator is separate from the record bias, and the record bias L is independent from the R. In a sense the deck has one erase oscillator and two independent record bias oscillators.

popcorn noise is Orange Cap Disease. OCD will give intermittent screwy auto cal results, so you kill that bird by changing the caps. Every 1000ZXL and 700ZXL should have the orange caps changed.

Intermittent channels are also caused by the external NR relay contacts.
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Old 11-03-2017, 05:05 PM
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https://imgur.com/a/k3vE3

Hello Tony

Following both service manuals standard and Limited, we can't find older revisions of CPU B pcb. The dip side wiring in my unit is about the same as shematics.
My pcb don't have the BM3 point at the pin 1 of IC805. It is the Brown cable, connected to pin 1.
Two 1 MOhm resistors in serie, perfectly selected to obtain 2 MOhm (1.012 + 0.987 MOhm) are connected from IC805 pin 3 (inv input) to J137 (CN-3 pin 6)
So it is not something you should worry about. The values and actual wiring are the same as in the shematics. I guess you have the first version and me the second.

Last edited by Matcs; 11-03-2017 at 05:10 PM.
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Old 11-03-2017, 06:44 PM
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Thanks Nakdoc, I wil order caps and logic gates soon.

Tony, Dan, Can you confirm on your CPU PCB 'A' that this trace is cut or not on your unit please ?

Beside that, many bad solders. CM7 (osc tones output) post wires bent trapped inside tied cables on the other side, and short-ciruited.


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Old 11-03-2017, 07:35 PM
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Hi Matyas,

My CPU 'A' PCB is not cut, my board looks like what is shown in my service manual, looks like yours has been cut to conform with what's in my service manual. Refer attached photo from my service manual. My manual also only has one version of the CPU 'A' PCB.

Tony
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  #20  
Old 11-04-2017, 11:53 AM
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Thanks for the info Tony !

https://drive.google.com/open?id=1vH...MkcJ3f5cxq_GtV

It's alive !

Just re soldered every points (excepted the ICs) on CPU 'A' PCB.

Last edited by Matcs; 11-05-2017 at 04:40 AM.
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