Here I tried to summarize some of my findings about the Panasonic パナソニック TU-AHD100(N) TV tuners.

What makes these units still interesting, is that they have an integrated MUSE decoder. It also has high-end (at its time, in the early 90's) comb filter, scaler, and can drive a CRT projector with an RGBHV signal output on BNC connectors. As a MUSE decoder it does a nice job, in my opinion it produces a pleasant "natural" looking picture, but picture quality is subjective, so I refrain from passing judgment on this matter.

One interesting feature of the MUSE decoder is the MUSE AI function (yes, the same AI! as the big hype nowadays). Well actually it seems to be a contrast enhancer (similar to the D-EXT for NTSC on Pioneer HLD-X9 LaserDisc players), which can render the image more enjoyable.

Okay, let's go and have a closer look then!


Table of contents

1. The Panasonic TU-AHD100(N)
2. Inside the TU-AHD100(N)
3. The MUSE decoder module
4. The "Component OSD Mod"
4.1. "Temporary Component OSD"
5. RS422 System Control Port
6. User Manual
7. Closing Remarks

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1. TU-AHD100 and TU-AHD100N

These boxes could do everything you just wanted in '93: BS tuner, VHF/UHF/CATV tuner, MUSE decoder, NTSC upscaler, comb filter, all the good stuff you can imagine back then. Although intended to drive a CRT projector, it has other outputs as well, including a component video out (HD monitor), which is still the most useful output to interface with modern equipment. Two variations exist, first the AHD100 came out and then approximately a half year later the AHD100N. N maybe stands for New version, but that's just my speculation. The user manuals mention 1993.09 / 1993.10 as the "current date" for the AHD-100 and 1994.05 for the AHD-100N.
Fig. 1. and Fig. 2. show the front and back panels of the units.


TU-AHD100(N) front panel buttons from left to right (Fig. 1.):

• Power
• Channel Up
• Channel Down
• Select Input - HD
• Select Input - TV/Video
• Select Output - HD Sound
• Select Output - M-N (MUSE to NTSC)
• BS Level
• Channel Settings

TU-AHD100(N) back panel connectors (Fig. 2.):

• 3-1 Stereo detect out
• BS Tuner Antenna in
• VHF/UHF Tuner Antenna in
• Converter Power ON/OFF switch
• 1x S-Video in
• 1x Composite in
• 1x Stereo audio in
• 1x S-Video Monitor out
• 2x Composite out
• 1x 4ch audio out
• 1x BS Composite in
• 1x BS Stereo audio in
• 1x BS Bitstream out
• 1x BS detect out (検波)
• 1x MUSE AFC out
• 3x MUSE in
• 1x MUSE AFC in
• 1x MUSE detect in (検波)
• 1x MUSE detect out (検波)
• 1x MUSE bitstream out
• 2x Digital audio out (1x Stereo for BS, 4ch (2x Stereo) for MUSE, TOSLINK)
• 1x HD component in
• 1x 4ch audio in (for HD)
• 1x HD component out
• 1x 4ch audio out (for HD)
• RGBHV video out (BNC)
• Video Projector Control port (DB25 male)
• Home Automation (HA) out (trigger)
• Screen Control port (DB9 female)
• System Control port (DB9 female, RS-422)

Fig. 3. shows the remote control, which is the TNQ10454.

I was interested in the MUSE decoder and the related things, so I focused only on those and ignored the comb filter, scaler, tuner parts. The difference I found between the TU-AHD100 and the little bit newer TU-AHD100N units is that the MUSE decoder is initialized noticably faster on the N model. Meaning that you will get a decoded MUSE output a few seconds sooner after powering on the unit. Also the software version labels are different on the two models, so maybe this is only a firmware update, at least what is related to the MUSE decoder. There is one small difference in the MUSE decoder hardware in the N and non-N models is, but it is indifferent from the viewpoint of MUSE signal decoding. You can find more details on this in Section 3.
From the outside there is no difference between the 100 and 100N models, the N is only shown on the back panel, the front panel says only TU-AHD100 even on the N models. There could be some minor differences in the scaler, tuners, NTSC processing, projector and screen control, home automation output control, but from the viewpoint of MUSE decoding the 100 and 100N are the same.

So what's in the box?

After removing the top cover, we can see the MUSE decoder module on the left and the NTSC processor/scaler module on the right (Fig. 4.).

These two modules can be folded to the sides of the box to reveal the whole mainboard and the two power supply units (Fig. 5.).

Under the metal box in the middle lies the main CPU (see Fig. 6.), which is a Hitachi H8/536 (HD6475368CP10) microcontroller. Since it is an a socket and should be easy to remove and to put it back without damaging it, the contents of its embedded ROM could be read with relatively little hassle. But I didn't do that, because I was mainly interested in this unit's MUSE decoder.

VFDs are always beautiful. In Fig. 7. all the display elements are visible, and Fig. 8. shows while it is on with the first MUSE input selected (but no signal detected).

Fig. 9. and Fig. 10. show photos of the top and the bottom of the MUSE decoder board for the AHD100 and AHD100N. Move the sliders for comparison, the AHD-100's board is from the left side, and from the right is the board from AHD-100N.

The decoder board uses 2nd generation MUSE LSI chips, and includes a MUSE-NTSC converter too. Many chips are possibly shared with the NEC HV-MD5000T [1].


I did not remove the mystery IC from the heatsink, as it is held on it with a strong, rubber-like solidified glue which also acts as a heat conductor. Therefore it's type or markings are unknown to me as of now.
You can find the full chip list at [1].

The MU1 connector is the MUSE out: white wires: pin1 Y, pin3 Pb, pin5 Pr, others (black wires) are GND.

The only difference between the two boards is that in the newer N models, one of the VRAM chips have been replaced on the bottom side of the PCB (see bottom left in Fig. 10., and Figs. 13., 14., 15.). On the older one, it is a NEC chip, on the newer one it's a Panasonic (this IC can be found in many other video equipment doing digital magic from the 90's). This makes no functional difference between the two, probably just a manufacturing issue. Maybe the NEC chip got obsoleted/EOL, or Panasonic got cheaper, but just right next to it and on the top side the same Panasonic RAM was already used (bottom right in Fig. 9.), so who knows.

For comparison of the boards again, Fig. 9. shows the MUSE decoder board found in the AHD-100 on the left side, and the one on the right from AHD-100N.

The On-Screen-Display is only provided on the RGBHV output (intended to be used with a CRT projector of the era), and not on the HD monitor output, which is a standard component video out, much more convenient to be used with current video equipment. The RGBHV out is also 1080i, which unfortunately most current video equipment will have a hard time to sync to (i.e. they won't), therefore cannot be really used with a modern TV or projector.

The decoded MUSE signal from the decoder module first goes to an other module, which is basically a switch for the different inputs (let's call it input switcher board from now on - see Fig. 16., Fig. 17. and Fig. 18. ).

From this input switcher board, the decoded MUSE signal goes to the HD monitor output, and also to another sub-board which puts on the OSD text and then converts the YPbPr signal into RGBHV. Fig. 19. shows this sub-board, and 20. shows a close-up of the area with the RGBHV converter.

When the AHD100(N) came out, the 1080i signal wasn't mainstream, integrated circuits handling these tasks for HDTV were not readily available, therefore the designers had to use what was accessible. The OSD chargen is the D6453CY chip, and the overlay is made by a combination of several independent ICs (Fig. 19.), and then this signal goes to the Sony CXA1478S IC (Fig. 20.), which then converts the signal to RGBHV. This means that we can tap the decoded MUSE + OSD signal when it is still in YPbPr.

I could not get hold of a real datasheet for the CXA1478S, so I needed to do some measurements and hands-on investigation. So it seems that the Sony CXA1478S IC is a component YPbPR to RGBHV converter and processor (hue, gamma etc.).

Table 2. shows an incomplete list of the Sony CXA1478S pins/connections in this unit:


Basically the signals we want travel on pins 1,2 and 3, and fortunately there are tests pins we can directly use: TPX1, TPX4, TPX5 (Fig. 20.). These signals should be passed through an amp/buffer/driver before releasing them to the outside world.
I experimented with integrating an additional switch IC to the input switcher board and leading these signals (with OSD) and the original no-OSD signal to this IC's inputs.

From the MUSE decoder board the decoded HD signal goes from the MU1 connector to the SA1 connector of the input switcher board. From there the flow of the signal looks like this (Table 3.):


So the idea is to tap the no-OSD signal before separated to the HD monitor OUT and the OSD/RGBHV processing parts. This is between Q4410 - Q4408 for Y, Q4412 - Q4409 for Pb and Q4411 - Q4407 for Pr. For the soldering points I used see Fig. 21. and Fig. 22. Also the traces on the PCB between these points should be physically cut, otherwise the signals will get messed up obviously. In Fig. 22. the locations where I cut the traces just before the transistors can also be seen. Then direct this no-OSD signal (from Q4410, Q4412, Q4411), and the OSD signal (from TPX5, TPX4, TPX1) to an switcher IC and tie its output to the HD monitor OUT (back to Q4408, Q4409, Q4407).

This way I could use the output drivers and RCA connectors already there for the HD monitor output. I reused the "Converter power" switch on the back panel (see the arrow on the right in Fig. 23.) for choosing between the OSD/no-OSD signal, as the BS receiver in the unit does not really have any function nowadays.

Basically I had a very simple circuit doing the job, but had problems with the signal stability in my switcher circuit in same cases, and I didn't finish debugging it, therefore I cannot publish schematics or circuit diagram here. But the above information can get you started if you are a bit into electronics and want to mod your AHD100(N) to have OSD on the HD monitor output. If you manage to build a working additional switcher circuit, please consider sharing it with me (kamm at laserdisc dot hu) and I'll put it up here (with proper credits of course).

If you just want to temporarily see the OSD, there's a much more easier and more convenient way. Use the Y output from the HD monitor output component out, and for the Pb and Pr (either one, or both) touch the hot wire of the RCA plug to the hot wire of the RGBHV BNC plug (Pb to B, Pr to R). It's OK not to connect the GND from the BNC connector as GND is already connected to the output device via Y and the other Pb/Pr RCA cable. But try not to short the hot wire and the GND. Something like as shown in Fig. 24.

The OSD image will be a little bit out of sync, as there are delay lines in the OSD and overlay processing part, but you can still see and use the OSD just to set up your unit, or experiment with features (e.g. MUSE AI on/off).

The system control port (システムコントロール入力) on the unit's back is actually a RS422 port as stated in its user's manual and can be used to do everything (and a bit more!) as its IR remote can do. Pages 74-75. (see Fig. 25. and Fig. 26.) of the user's manual describe all the necessary details on how to communicate with the unit.

Based on that, I prepared this simple python based tool to interface with the TU-AHD100(N). I called it TUAHD100 Commander. Also I made a nice fancy (right? :-) ) GUI version partly imitating the TU-AHD100 IR remote control (Fig. 27. vs. Fig. 3):

And a CLI version (screenshot shown in Fig. 28.), supporting all the commands the TU-AHD100(N) can understand:

You'll need Python 3 and pyserial, and pySimpleGUI for the GUI version.
(Just do pip install PySimpleGUI pyserial).

And the necessary hardware to connect to its RS422 port (bottom left of page 74. (Fig. 25.) shows the pinout) from a PC. I built one using two MAX485 ICs, a Serial-USB converter, a male DB9 connector and two resistors. This way I could directly connect it to a PC with a USB port. Fig. 29. shows a sketch I draw for myself before started soldering. Not the nicest but could be useful for someone who wants to build one too.

Of course other ICs could do the job, like the ADM485, LTC1485, etc. If you only want to send commands to the unit and not interested in the reply (ACK/NAK), then one MAX485 is enough. In this configuration try using the simplex mode in the above mentioned python utility (see the simplex parameter of TUAHD100_RS422 class) [2]. In theory it could be even possible to implement half-duplex communication.
If you have a Raspberry Pi or similiar with a TTL UART lying around then you won't need the Serial-USB converter, just connect the MAX485 to the corresponding pins for the UART on your single board computer.
Or if you are up to more challange, then you don't even need the MAX485 ICs. The bottom of the mainboard hides the the RS422 transceiver chip (IC1008, which is a Mitsubishi M5M34050 [3]) in one of the corners near the main CPU.

Here it might be not so difficult to trap the TTL level serial communication, but considering the amount of work needed to access this chip and tap the wires here, building a RS422->RS232/TTL UART converter for the "external" control port is still easier to do. You can decide :-).

The manual for AHD-100 can be found on LDDB's manual archive [4]. Later, here I will share the manual for the AHD-100N. In color!
A few differences I could spot between the AHD-100 and AHD-100N manuals are so far:

• p. 71. the "current date" is updated from 1993.10. to 1994.05. and the channel lists are also updated.
• p. 72. the "current date" is updated from 1993.09. to 1994.05. regarding the availability of the "Sensor Controller" to be attached to the "Home Automation Control" Output.
• p. 73. a new short section appeared about HALS control on/off.
• p. 74. the command list page for the System Control (RS422) commands has been updated and one code has been fixed.

Until then, enjoy the front page (Fig. 31.) of the manual and the "Quick Start" (TV Tuner - Easy operation) card for the AHD-100N (Fig. 32. and Fig. 33.). You can also download it in higher resolution as one PDF file from [5].

7. Closing Remarks

References

[1] GitHub:szaguldo-kamaz/laserdisc-kamm - Panasonic TU-AHD100 IC list
[2] GitHub:szaguldo-kamaz/laserdisc-kamm - Panasonic TU-AHD100 RS422 control application
[3] M5M34050P Data sheet
[4] Panasonic TU-AHD100 User's Manual @ LDDB
[5] Panasonic TU-AHD100N "Quick Start" card