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HP5430A 18GHz微波计数器维修+测试 / Microwave Counter Repair+Testing

这其实是2019年11月完成的事情，当时拍了一些照片记录，不过因为拍摄环境限制拍得不是很好，就没发出来。最近本科快毕业了，在考虑离开学校的事情，整理了一下自己在学校外租的，专门用来当实验室（事实上更像是仓库）的出租屋。这台仪器作为所有收集到的仪器中个人最喜欢的一台，作为一个纪念，还是发出来了。 HP5430A是HP Journal 1973年第4期的封面产品，这是一款量程覆盖10Hz~18GHz（加选件后可进一步提升至23GHz）的采样式微波计数器。和同期推出的，搭配180系列示波器使用的采样头一样，这台仪器的核心是HP在当时刚开发出来的20GHz采样模块。 实现18GHz的测量并非难事：使用一些微波技巧和当时速度已经足够快的射频二极管，通过混频的方式就可以将高频挪到低频。但是这样做的问题很明显：一个混频器+本振+相关的滤波器只能实现窄带测量，所谓窄带，在当时来说就是300MHz的量级。如果希望测量10Hz~18GHz这样广的频率范围，使用混频方式的成本和制造难度是超高的，只有在频谱仪这类“通用仪器”中才会采用。对于计数器这种需求略有不同的专用产品而言，HP采用了一种基于采样，也就是频域卷积的解决方案，大幅降低了成本。将简单来说：该仪器在工作时，利用采样过程导致的混叠，将微波信号“折叠”到低频，再用普通计数器计数，再去反推原频率。该仪器采用了一个巧妙的方式实现了折叠次数的判断，具体实现方式可以阅读这一期HPJ，Youtube上也有几个视频中有讲解。 作为当时HP微波产品线毋庸置疑的高端产品，这台仪器的售价达到了1973年的$5900，换算到今天就是2019年的$34428.58，约24万RMB。因为当时做高频ESD防护和高频信号限幅很困难，这台仪器的输入保护远远没有现代射频仪器那样完善，真正实现了摸下就死——指现实中的。以至于机器的上面贴了一块金属铭牌，特别强调：“警告：向50Ω输入端输入大于+30dbm（1W，7.07Vrms）的信号将造成严重，且维修费用高昂的损坏”。 温馨提示 因为以上的这些原因，购买前我非常犹豫。这台仪器已知有相当多的故障，前端，也就是价值最高的部分好坏未知。最后还是看在它有辉光管显示屏的份上，付了一大笔运费把它买下了。想着：如果实在没救了，改造成一个超重的辉光钟也不是不行。 首次通电 收到机器，检查变压器设置没问题之后通电测试，状态就和卖家...
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A Modern Reincarination of Graphire: WACOM Bamboo Series Drawing Tablet Reverse Engineering

This is going to be a short follow-up of the previous article; please read that one before proceeding:  https://www.lithcore.cn/2024/02/wacom-et-0405-reverse-engineering.html.

Same as before, all the high-resolution PCB scans have been uploaded to GDrive: https://drive.google.com/drive/folders/1vGHHMH9WkavLYoCPT2HWrooUTZOjV1wc

I'm personally attached to the Bamboo product line because that is where I got started 10 years ago. The Bamboo product line is initially made of cheap pen-tablet products designed for the entry-level market. WACOM intentionally limited the performance of those products to avoid direct competition with their professional Intuos product line. 

Interestingly, by the time I started using their products, WACOM had gradually shifted the focus of this product line to experimental and high-diversity products, including mobile phone styluses, ultrasonic pens (The first Bamboo Inkling product), mobile phone applications, and paper-based products (e.g. Bamboo Folio and Bamboo Slate). Meanwhile, the low-end pen tables have been relocated to the "Intuos" (not "Intuos Pro") line and, subsequently, the "One" product line.

CTH-470

This article is about the Bamboo CTH-470 pen tablet. Surprisingly, the design is almost identical to Graphire's, with no ASIC chips on board (except for the one in the pen). It's quite unusual, considering WACOM's tradition of making ASIC chips since the very beginning.

Backside of the PCB

Captured Waveform at the Integrator's Output

The output waveform is simplified compared to Graphire's. Notice that the pressure resolution has been upgraded to 10 bits instead of 8 bits.

This model also supports capacitive touch using an Atmel chipset. 



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