After opening my Lexicon LXPs, I realised that the batteries are on their last legs and I need to make an order for battery holders. Research led me to the Adam Tech, BH-76A-1 which is meant to be a good fit for the board. The only problem is that to get them at a decent price, I will need to buy in bulk to get a good shipping rate or combine with other parts.
My conclusion is tha it’s best to use this opportunity to see what types of mods are available and buy parts in a bulk order.
To open up an LXP-1, I recorded a video that can be found here:
So here goes, what other types of mods are available for the LXPs. Please note – use with caution, I may have mistyped or misunderstood! I found the following:
Pots:
- Replacing PCM54HP chip to PCM54KP (covered in depth in another post: link)
- Cleaning Pots and Encoders.
- Bypassing bad pots
- Replacing Pots
- Power supply capacitors
- Op-amps
- Headroom Mod
- Reflex RAM solution.
Information about opening and cleaning pots can be found here [link] and encoders [link].
Bypassing bad pots can be found here: [link] and involves 15k and 2.2k resistors. I’ll probably head this route when the pots go because I can control nearly everything through my own editors.
Pot replacement details can be found here [link]. I contacted the company directly to find the part number used in the Lexicon and to see if I could find a modern equivalent. There were modern parts produced for it but they are out of production and hard to track down. I included all of my research, including part numbers, at the end of the blog.
Power supply capacitors:
From 211 [link] for the LXP-1
- Removed hum: Replaced all 1000uF PSU electrolytics and 7805 (regulator). The information about the regulator is slim which means I do not know how to replicate it.
- Additional scratchy noise: spraying contact cleaner (with caution – do not degrade the carbon) in the pots removed the scratchy noises.
Jim Williams [link] for the LXP-1
- Replace 1000uf caps with 2200 uf 25V Panasonic HD caps, same size as the original 1000 uf.
- Add a Pair of 470uf/25V caps on the power lines near the jacks for extra filtering. I would like to find out more about this. and lack information here.
LXP15: CFCreative (link)
- “All new Nichicon Fine Gold audio capacitors in the audio processing circuitry of my LXP-15. Swapped 22uf for 47uf and no problems.”
- “I can’t remember exactly but if you open the case there is 5 larger capacitors in the power supply then about 25 small ones. https://s1299.photobucket.com/user/E23N42SF/Lexicon%2520LXP15%2520Inside/story replace the coin battery as well at the same time.”
Op-amps
- If I have read this right, 211 was thinking about replacing input opamp U30 by a socket, and try TL072 and OPA2134 but it looks like this would not have much in the way of impact.
- Jim mentions that the stock signal 33078 opamps are ok and there is no benefit to use high test opamps there as the 16 bit conversion will wash that out.
- Jim recommended opamps: ADA 4625-2, about $11 each for sample and hold to increase quality and resolution but I need to work out what this means and where to do this. I cross referenced another Jim post here: and additional [link]. To understand more, I posted a follow-up question.
- 211 replies, I’ll add extra caps … and try small 47pf or 33pf caps in the feedback loops of the amps.
- Jim mentioned replacing the timing caps with polystyrene
Headroom Mod
A good chunk of information can be found here [link] and [link].
- Jim mentions the front end opamp has too much gain. It’s a 330 ohm gain shunt resistor with a 10k feedback and [link] “The front end opamp has too much gain. It’s a 330 ohm gain shunt resistor with a 10k feedback. I change that shunt resistor to 3.9k ohms, that allows about 10 db of gain. Then +4 has the input pot at 1 o’clock.” Looking at the manual, I can see 3x 330ohm resistors. My thoughts are it is one of these but I do not know. Therefore, I posted a follow-up question.
Chip Upgrade:
Chip upgrade (various) PCM54HP chips to PCM54KP link] and link]. Eprom Chip Puller needed.
Reflex RAM Problems:
For Reflex RAM chip problems:
Really good video. Very useful about the chip itself. Texas Instruments DV41464P-10. I saw a note in the comments saying that if the part Texas Instruments DV41464P-12 (12ms) is available, use that. If you’re out of luck with a Lexi specialist, it’s worth getting the chip and checking with a local repair company that specialise in soldering.
Reserach: Pot Research and Potential Leads
In this section, I cover the research completed. Sadly, it did not come to anything viable but thought it worth addin to the bottom of the blog for reference.
I did call Lexicon and they were only able to tell me that the Input (first knob), mix and output (second and third knobs) used the following pots 1 – 10KBX2 and
2 – 50KAX2 but could not tell me which one was the input knob.
Additional information from Modwiggler and a link to this advert: [link] 5 pins straight across? maybe not. A later post here [link] indicates it is different, akin to picture 2. From the service manual [link]. “2 SW,RTY,BSCD 16 POS, 16 position rotary encoders”. LXP 4 Bit encoders and datasheet [link] and mouser listing for manufacturer [link].
I opened mine up and found the following pots: 452-06045. Searching in Google returned the following: [link] for 2bit encoders and looking up in Digikey returned a great match in datasheet [link]. Okay, so there are several codes. Searching found [link] the original 288 switch is an inverted GRAY-CODE encoder.
From the sheet on Digikey, there are several options:
| 288 | T | B | 24 | F | 40 | 2 | A | 1 |
| – | Termimal | Bushing | Length | Trim | Resolution | Code | Switch | Detent |
| 288 | X | ? | ? | F Flattened | ? My guess is 16 | 2 Gray | B Momentary | 2 16 Detents |
V:\Dept\MK\編輯用舊資料\Modify Folder\最新VR(可編輯檔)\~$288-1 2017.10.11.pdf