Project Time! #3

What can one do with a piece of vintage tech like HP 6920B? I found a few uses for it already:

  • testing “magic eye” tubes that require some 250V for anode/screen voltage
  • testing capacitors for DC leakage up to 1kV
  • reforming electrolytic capacitors
  • testing gas-discharge voltage-regulator tubes
  • testing Geiger–Müller radiation detectors
  • testing electroluminescent backlight panels
  • testing transformers (ratios, self-heating and winding insulation)
  • and zapping stuff with 1kV AC/DC

I’m probably going to invent some other uses for it as well but originally I wanted it for some repair fun and one particular purpose – as a 1kV DC source to recalibrate my AimTTi 1908P multimeter:

First let me introduce the 1908P a bit. I got some other AimTTi gear as well so I expected their multimeter to be decent. Different people have different needs so here’s my personal pros and cons lists:


  • 5 and 1/2 digit modern digital multimeter with reasonable specs
  • it’s cheap, even taking into account Chinese offerings like Rigol and Siglent
  • has Ethernet port for TCP/IP connectivity (as well as serial and USB, and GPIB/IEEE-488 if you need it)
  • no fan, no noise, no holes in the case for the dust to get in
  • 2s boot-up, of which 1s is the display test
  • decent screen with good backlight
  • manufactured in Europe
  • built-in battery pack for off-line operation


  • it’s only 120k counts
  • not very fast, 4 readings per second at full resolution (less in dual-measurement modes)
  • no rolling averaging to reduce input noise
  • diode test goes only up to 1.2V due to non-selectable range even if the output voltage is about 3.5V
  • only 10M impedance on input on DCV ranges (less in AC mode obviously)
  • built-in battery pack for off-line operation

I’m really starting to dislike USB these days. I use it a lot and I’ve seen all kinds of issues with it – cable length problems, flaky hubs and connections in general, driver problems. In fact custom, broken, never updated drivers are the worst and can often interfere with other devices that worked perfectly before. So I always look for Ethernet ports on new equipment, I don’t trust hardware manufactures to come up with decent drivers or any at all if you aren’t on Windows or it’s not the version they support. Serial port is second best option but it’s slow and typically offers no HW error correction, so a single bit glitch in the data stream can easily bump a digit up or down in the reading and you’d never know it. GPIB/IEEE-488 is… old. And costly. And very proprietary. If you already use it a lot you won’t mind but newcomers are better off looking for something else.

The 1908P has Ethernet port and it’s a huge plus for me. And the price is still acceptable, unlike say Rigol offerings that give you cheaper USB-only models or the full-fat ones for 500 USD more. The 120k counts is more of “5 digits” than “5 and a half” in my book but I’m not going to argue with established shady marketing, it’s not just AimTTi doing this. I very much like the no-fan design and the LCD display is OK, not great but also not annoying me in any way. The battery pack is a bit of a double-edged sword – nice when you need it but keep in mind it will die at some point. Mine in fact did (was probably defective) and that most likely caused the brick I had when updating FW – AimTTi did good though and repaired this for me for free.

No averaging, 10 meg input and limited diode mode are not great but also not a dealbreaker. I might at some point need more than 4 reading/s at full 5-digit resolution but I don’t yet so that’s also not a problem. All in all I am happy with the price and performance – or rather, I was, until I discovered a glitch.

Long story short: When in 1000V DC range and below 100V (so only with manual ranging) there is a weird non-linear jump at exactly 99.00V that skips all the .01 to .05 values and goes to 99.06V (so from 99.00 to 99.06). I asked AimTTi about it and they suggested recalibration of the 1000V range. Turns out the calibration procedure requires a 100V input at one point, which is pretty much the only thing I’ve changed in the calibration data and it only made the “99V problem” worse. So clearly the jump/skip is some sort of FW issue that tries to improve the linearity of this range by having both 100V and 1000V references stored – but messes up the cross-over point. At least that’s how I see it. AimTTi has since ignored 3 of my emails – both about this issue and another one with their MX180TP PSU.

I’ve read many good things about AimTTi support but I have to say my personal experience with them is spotty at best. They will fix bricked equipment and issue FW updates for the serious bugs (not to brag but the Interface firmware version 1.07 for MX180TP exists because of me). The less obvious stuff though? Won’t even reply to the email.

And so, to conclude this – would I buy this multimeter again, knowing what I know now? Yes, it’s not like Rigol/Siglent or the Keysight/Keithley (which are often made by Rigol/Siglent in the lower price range anyway) have spotless record when it comes to FW bugs. And the price is still very good. But can I recommend AimTTI to others? No, I can’t. If you really need a good bench meter then you should probably look into the (considerably) more expensive K-brands. If on the other hand it’s for personal use then Chinese meters have more features, color LCD graphical screens and you probably won’t mind having just the USB available anyway. Unless you live in UK and can drive to AimTTi in person if need be.

84 thoughts on “Project Time! #3

  1. Is there a carrying handle on the 1908P?

    Also didn’t know you own radiation detector. That’s a jump from antique radio and calibration tools.

      • I’ll “consider” this review.
        I need a reputable multi meter with the projects I’m getting involved in. $30 special won’t cut it.
        The siglent SDM3055 is noticeably cheaper though and still does Ethernet. So toss-up.

      • Siglent lowered their prices recently, but AFAIR their meter used to take 20s+ to boot from the moment you pressed the power button. Supposedly the latest FW has improved it but I don’t know by how much.

        Which reminds me to add another point to 1908 pros.

      • Unacceptable 😉

        I would be very interested to see the natural drift of a ’60s-’70s radio calibration tool (with all stock components serviceable) compared to something modern like a rigol or siglent brand tool. Would require a lot of equipment though

  2. Hi sorry to post here but I don’t know where to post bug reports.

    Has anyone been able to get Vandal Hearts the recent translation working on Rhea?

    When I try to boot it up it freezes at after the introduction FMV when you press start

    Where it says 1254
    Gillbaris Island

    “Castle Ruins”

    • Haven’t tested that and currently got no free time, but if noone else helps you keep bugging me and I will check.

      • I managed to get it working by using iso format but when I put in the 4mb ram cart which this hack is supposed to work with seems to lock the game up.

        The other formats I have tried mdf / mds I couldn’t get to work at all
        the one I usually use is ccd but that one seems to trigger the 4meg mode.

        The iso version that I extracted using iso buster from the redump version works properly.
        I was using Alcohol 120% to rip the game after mounting the redump version.

        cdi’s I haven’t been able to rip since Windows 10.

        It’s an issue with the 4meg ram mode for sure.

        He mentions pressing L+R for Psuedo Saturn cart but that didn’t work for me

      • Hey,
        If you could link me to whatever iso you’re using I will burn it and see if it works on my stock Saturn with my pseudo Saturn cart.
        I also have an original Japanese Saturn that I could try as well.
        If this would help any, let me know!

      • PS

        If you could image the disc you’re using and link it, that will work best for me. I have a lowly DSL line here in the country and it will take me forever to download all that stuff and then patch it, etc.

      • Hi,
        So that didn’t take as long as I thought it would!

        Grabbed the image from redump, and the English patch, patched image successfully, burned it with imgburn (what I always use) on a standard memorex CDR.

        Here’s my results FWIW – (I don’t have a RHEA)

        Oldest unit unmodified – oval buttons with power supply in the top case:
        No boot with Action Replay (hangs at loading notice) or Pseudo Saturn cart.
        I tried the L+R immediately after selection ‘automatic’ on pseudo saturn cart – the ‘caching data’ notice didn’t come up, but the game never loaded either.

        Round button unit – Phantom mod:
        Booted game and played past the ‘castle’ screen with no cart, action replay cart, and pseudo saturn cart. Got message every time about no room to save, though – and the action replay is new.

        White Japanese Saturn unmodified:
        Booted game and played past the castle screen with pseudo saturn cart.
        No boot with action replay cart (hangs at loading notice)

        Hopefully that helps!
        Good luck.

      • I guess the game was modified to work with emulators and not actual consoles. Or tested with one particular console that might also be modded.

      • I was surprised that it worked on the unmodified Japanese Saturn with the Pseudo Saturn cart. I couldn’t get it to work with a stock US Saturn (oval buttons).
        The upside is that I now have another interesting game to play on my Saturn!

      • It’s rare but some Saturn games check the region in the game code as well (that’s an extra check on top of the usual BIOS disc lockout). Might be such a case?

      • I’m pretty sure I did it right, as it was only – run the file, patch ok, etc. But I’ll have a look for the prepatched iso as well and see if that makes any difference. Mainly, will it work on the unmodified oval button Saturn with Pseudo Saturn/Action replay.

      • Hi – tried the prepatched ISO with the same results – at least on the oval button Saturn. It won’t load with either cart – Action Replay or Pseudo Saturn.

      • Makes sense I guess my Sega Saturn is a Japanese one it does load up but you have tried it on a US one.
        He should add some fixes to it I think it could be true that it is region locked and made to work with emulators

      • Could be – My trusty round button one that’s Phantom modded will usually play anything, and the cart port is the most reliable as well.
        Which reminds me, have you fiddled with the cart some (power off) to make sure it’s connected solid? Sometimes the load screen will come up but it’s still not connected fully and doesn’t work correctly.

        Good luck, and I hope you get it working!

      • I got it working on Rhea after using isobuster to extract the iso from the patched redump file.

        However for me it only works when I don’t have the ram cart connected.
        I tested it on Street Fighter Zero 3 first so I know it was connected properly

      • Good deal,

        Sometimes it’s the easy stuff that’s also easy to overlook.

        Hope you get it working with your Rhea. Looks like a good game – after I finish Shining The Holy Ark, I’ll probably try this one next.

      • Hi,

        To further the compatibility.
        I read on the Sega Saturn forum that the game was stalling exactly where I was stalling on the FMV into but MODE has had a firmware update and it is now working with the 4mb ram cart mode also

        Please look into this as I would also like it to work.


      • I can look into it when I have some time – but if it turns out it’s a bug in the patch and the FW fix is just a game-specific hack to work around this problem, then I might not fix it. Reason being the people who make these patches should test it on real HW and not rely on emulators and/or ODEs fixing the issues for them.

      • There is one thing though people that are making these translations may not have access to an ODE.

        The most I have seen them talk about is Pseudo Saturn cart.

        People are talking more about MODE now since that is the one that is most easily available with better compatibility than Fenrir

  3. I’m not sure if that’s allowed here but the prepatched iso is available online if you look for it

  4. Otherwise, it’ll take a couple days, but I’ll give it a shot!

  5. good afternoon
    Tell me please!
    I really want to buy gdemu
    when will it be on sale?
    thanks in advance

  6. Hello there, quick question about the “read_limit” parameter for GDEMU. Your documentation states the following:

    Where N is natural number in range 600 to 1250 (in KiB/s), or 0 to disable and -1 for automatic limit. If enabled (N 0), GDEMU limits media read speed to better match actual GD-ROM drive. The automatic setting will only affect games that need it. Default is auto.

    Does this mean that if “read_limit” is undefined or set to automatic (-1), the read speed is always 0 unless a game is on your hard-coded list that requires a different read speed?

    Thank you! =)

    • Yes, that’s exactly how it works. This way there is no slowdown in games that don’t require this workaround.

  7. Gdemu question, I’ve been told in the reddit dreamcast community that the L and R triggers fast scroll across your game list, told by a few people at this point. However, thats not the case for me. L and R do nothing in gdmenu. Is this a fix I can do on my part?

    • Also

      I wanted to reply to our last conversation concerning Virtua Fighter on the Sega Saturn using Rhea but the comments got closed

      My Sega Saturn is a one that works with Rhea Mk1 Grey with Blue Buttons.

      I did some additional research and apparently Virtua Fighter 1 has issues with flickering in emulation generally.

      So I am wondering if the way the ODE works is causing the flicker.

      It would be nice to have this fixed as I am hanging onto my Sega Saturn with discs just to play that game when I feel to.

      It’s hard to find information on it but I found out about it when watching a video by modern vintage gamer

      • Kingston 128gb SDXC Class 10 Speed right now but I have used others all with the same issue.

      • My reply was meant for jakersak :p

        Is this issue prevelant when playing on CD? Sometimes the CCD rips floating around are questionable. You can try to find a redump image and convert to CCD if you are concerned.

  8. @gdemu


    I wanted to reply to our last conversation concerning Virtua Fighter on the Sega Saturn using Rhea but the comments got closed

    My Sega Saturn is a one that works with Rhea Mk1 Grey with Blue Buttons.

    I did some additional research and apparently Virtua Fighter 1 has issues with flickering in emulation generally.

    So I am wondering if the way the ODE works is causing the flicker.

    It would be nice to have this fixed as I am hanging onto my Sega Saturn with discs just to play that game when I feel to.

    It’s hard to find information on it but I found out about it when watching a video by modern vintage gamer

    Also please delete my last post replying to cyo.key.leemur I was messaging on my phone at the time and it gets confusing

  9. Hey D,

    What was your settings for SCSI2SD? I’m trying to retrofit a scsi2sd 5.2 inside an external SCSI hard drive for towns.

    Fun fact is that the external SCSI drives from back in the day for towns don’t have any special circuitry in them. Just a PSU and direct cables to SCSI50 port in the rear to the SCSI hard drive internally. It’s clicking super loud and not recognized in townsOS despite partitions being allocated in townsOS. I just thought this would be a fun project to retrofit external drive with modern drive 🙂
    Anyway sorry to ramble I was hoping you may have written your settings down somewhere.

      • Yup, I don’t remember doing anything special there, if there was anything at all it would have to do with termination since I was running the SCSI2SD on terminator power alone.

      • Yes it’s very convenient.

        I discovered last night you can directly wire a scsi hard drive directly to the centronics 50 port. I found the pinout in the 900 page programming manual for towns and you can wire a 50 pin female box header from let’s say a 3foot centronics50 cable. The hard drive enclosure I bought is just a scsi port directly wired to hard drive with no interfacing board required.
        Also don’t use scsi2sd 5.5 with towns it doesn’t work. I thought it would be a good move since you used the DB25 port on the 5.1 so I tried out the 5.5. I can’t get the towns to see the 5.5 in townsOS and it also and this part is going to be weird. You may have to read it twice as it sounds insane.

        If the 5.5 is plugged into the towns it forces the pc to turn on. If you remove it while the pc is on, the pc turns off and you can’t turn the pc off with power button when it is in DB25 port.

  10. @GDMU

    I have a strange crash bug with using a Doc Brown ODE with the game “Kyuuyoku Tiger”.

    When booting it, as the 1st game I try after powering on the console using the Almanac menu, it hangs on the Towns OS screen.

    However, if I reset the Marty console when it hangs on the Town OS screen and choose a different game in the menu like “Splatterhouse” and then reset it again after that game loads. “Kyuuyoku Tiger” will work fine and no longer hangs on the Towns OS screen when selected a 2nd time.

    If, i power off the Marty and back on again, the problem will occur again until i do the aforementioned steps again.

    I have tried 3 seperate SD cards and sizes and had 1 other person confirm the same problem, yet the image is from the “Neo Kobe” set, which ain’t great anyway, as a source of files (says mp3 source) and I don’t think there is a clean redump of it atm.

    I have tried over 60 games that load fine on first attempts and only this one gives me this weird issue.

    • I’ve heard this game is problematic but I could never reproduce any issues – though this is the first time someone said it only happens on the first boot attempt. Anyway, did you test it on 1.6.0. FW or earlier?

  11. Hi,

    I’m still using 1.5.1 FW. Cyo.the.vile confirmed the same issue on 1.6.0 FW for me.

    • Well, it works for me. Both through Almanac and booted directly from folder 01. Boots every time though I’m not sure if I converted the image properly as I don’t have any CD audio in the demo mode (but maybe there isn’t any?)

      Did you try direct booting? What do you have in your INI file?

      • Interesting. Okay, I’ll check it direct and look at my ini settings and get back to you.

        Btw, i converted the image to CCD/IMG clone CD format. There is music in-game but not on the demo mode.

      • @ Deunan

        My Ini Settings

        open_time = 500
        detect_time = 250
        reset_goto = 1

        A fresh 8GB Kingston SD card formatted to FAT32/32K Clusters. 01 folder on the card with the game files in CCD/IMG format along with the doc brown.ini on the root.

        Direct loading still results in a crash on the “FM Towns OS Version 1.1 Level 30” message screen.

      • Try disabling overclock, since that’s on by default, and if it doesn’t help then either your copy of the game is converted differently (might be a factor) or it’s down to me having a 486 in my Marty. We won’t know until there is a good dump and it’s not a bloody CUE+BIN.

  12. I have found alternative option to use external hard drive on all FMT models. This discovery came with disassembling my external SCSI hard drive I bought. I tested this on CX20 and UX20.
    All you need is CN50 to IDC50 cable. Took a bit to find it. You won’t have to rip apart any towns PC except of course replacing the internal battery. Hope this can help you and any other follower with towns pc

  13. Using a phoebe on a model 2 saturn. When it comes time to swap a disc in a game I push the button when prompted and it resets to the cd console and displays 1 track and 0:06 (which is the rmenu) instead of progressing to the next disc. It’s been a long while since I played a multi disc game on here (deep fear) but I swear it worked when I tried it then.

    Any body have any suggestions?

    • ODE will go back to 1 if the image you are trying to load is missing. Are you sure threre’s no gap in the numbering?

      • Just double checked. No gaps in the numbering and all the images load individually.

      • Does the button work properly in the CD player menu? Perhaps it actually works OK but the console goes back to menu on disk change when run from menu – this might be some side effect of using fastboot. Try full boot as well. Also, do you have any carts inserted, like AR or memory pack?

      • I tried full boot like you suggested and that did the trick. I tried it with the official memory cart, Action replay and without a cartridge and it all worked. I must have used full boot before and forgot about it, I’ll have to keep it in mind going forward.

        When prompted to switch discs it still boots out the cd console, but the correct disc is cued up and I can start it from there. That’s the normal sequence correct?

      • Frankly I don’t know, seamless switch makes more sense but perhaps a boot was required to go through the SEGA copyright routine – which is how they enforced their licensing. If it works, it works 🙂

      • Not sure how it works with discs as I bought my saturn specifically for your ODE lol. But you’re right, if it ain’t broke don’t fix it.

        Thank you so much for your help!

  14. Hello

    I allow myself to post this message even if it is not really the subject to know if you went to manufacture again an ODE for FUJITSU FM MARTY, I have just acquired this console and I am replacing the capacitors, after I am not sure that the optical unit works, thank you in advance for your answer.cordially

  15. Hi GDEMU,
    I bought a GDEMU v5.5 20017-09-01. It has in the past worked great. I went to use it recently and it just gives me a Black screen and then the Dreamcast logo. It eventually goes to the Dream Cast menu and says trying to load disk. I tried removing the SD card, and switching to a new Dream Cast. None of that seems to make a difference any suggestions. I don’t think I upgraded the firmware. Any suggestions on what to do to get it working again. I tried emailing the address that was attached to my paypal receipt but I never got a response from you. (prob not a used email).

    • I’m pretty sure it’s a PSU contact issue again. Disconnect the cord and then wiggle the PSU board up/down a tiny bit right next to the mobo pins – just enough so that the connector moves vs the pins. This is usually enough to break through the oxidation, at least for a quick test. Then reconnect the cord and see if that did anything.

      • I tried, that. on both of the Dreamcasts I currently have open it didn’t change anything. I did also check the voltage between 3.3 and GND. One had the voltage at 3.7 and the other at 3.8. Also the led on the board is a solid orange. (No clue what that’s tied to, but in case its important.) On one of them I also tried just moving it up slightly so that it would be on a different spot on the pins.

      • By “led on the board” do you mean the status LED on GDEMU? It’s always on, doesn’t even blink or anything?

        And since you have the meter, do test on GDEMU directly as well. Use first and last of the holes in the vertical row next to status LED. You should see 3.3V here, +/- 5% max.

      • Yea the LED just turns on with the system LED and never blinks. The Dreamcast it’s in right now, has the same voltage across those test pins of 3.8V, looks like that’s a variance of 15%.

      • 3.8V is too high. If it gets anywhere closer to 4V it will start frying chips (right now it’s only degrading them faster).

        Fix or replace the PSU, if that doesn’t solve your GDEMU problems then I’m afraid there is a good chance it has already died. You will have to send it back to me for repair.

      • I guess bad luck then, that I bought a replacement DC and it had the same issue? What do you recommend? Any specific replacement PSU, or to re-cap, and replace the regulators? If it has to be repaired, how do I contact you about setting that up?

      • Console5 has capacitor kits you can purchase for your Dreamcast power supply.
        If youre outside USA and don’t wish to wait for shipping you can also use the values on the tech wiki

        It will show you Micro farad and voltage ratings. You can look on an electronics distributor like Mouser or digikey and order proper capacitor replacements. It’s beginner level soldering to replace those capacitors if you have iron and de solder pump.

      • Cool, thanks wasn’t sure how capacitors could make the voltage go up, so was wondering if it was something else. I’ll try that then. Grab two kits and fix both of them.

  16. Hello. Sorry to hijack the comments of this post to ask but couldn’t locate a contact address or a relevant post with open comments. Had a quick question about the FW update process on the GDEMU. Followed your instructions to the letter but I cant see to get past even the updater FW step. I renamed the updater file to GDEMU.fw, placed it in the root of my SD (both with GDMENU on it too and with a blank SD). I lock the SD card, insert it with power off and boot the Dreamcast. There’s the fast blink at power on but then the LED shuts off and the Dreamcast just boots to the main menu screen. It doesnt appear the GDEMU is reading the FW update. MY GDEMU shipped with 5.20.2 and was thinking I’d update to 5.20.3 since it was available. Any suggestions as to what to do would be appreciated. Is an update even necessary? Is having a DCDIGITAL (Formerly DCHDMI) installed a complication?

    • Maybe a silly question but people do make this mistake quite ofen – are you using SD socket extender of any kind? If so, remove it and use the GDEMU directly.

      Also, rename the file to GDEMU.FW and not GDEMU.fw (and when instruction says to first rename the file, and then copy it to the card, you are supposed to do it in that order)

      Any why are you even trying to run the updater if you already have 5.20 FW?!

      • Yep theres an SD extension. Ill try removing it. As far as the updater i guess i need clarification on that as well. Was the updater NOT needed for 5.20 and beyond? The instructions kind of make it seem like you need the updater before each firmware update.

      • Huh. The page says: IMPORTANT: Devices shipped prior to 2020 and running on FW older than 5.20.0 require a special update to be applied first.

        There were no 5.20 FW GDEMU shipped prior to 2020, and you did know you have it installed anyway. I can change the warning but frankly I don’t understand why it confuses people? Do I need to implicitly state the opposite as well? That anything with 5.20 and/or shipped in 2020 or later should not use the updater?

      • Nevermind! Removed the extension and used the 5.20.3 file only and it flashed perfectly. Thanks!!

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