HP16500  - Page 1
Forum section: electronics / testgear

author: mattbrockuk
author_rank: Contributor
timestamp: January 13, 2017, 11:45:27 am
content: Hi guysI picked up a second hand HP16500(A) model... it all fires up into life but occasionally you can hear a HV crack type sound followed by a bit of fizzling, the unit is still functional when this happened (although to be honest i unplugged it soon after).Looking inside, its pretty filthy (the case was horrible, alchol wipes have made it much better), and I've read that dust etc.. around the HT voltages of the CRT often cause this HV crack sound - not sure how true this is - i've not played with CRTs before.Obviously am aware its HV, but thinking of stripping it and cleaning it and checking the caps etc.. for bulging.Does anyone have any other thoughts?CheersMatt

author: vealmike
author_rank: Regular Contributor
timestamp: January 13, 2017, 12:11:48 pm
content: Its a long time since I repaired a CRT.Sounds like a fault with the insulation in the line output transformer or it's HT lead. It's something we saw regularly with PC monitors long long ago.This is HT, you know it's HT, it will bite if you get it wrong. HT is present long after the set has been powered off.Approaching this one, you need to assume that anything in the LOTX and the HT lead could give you a nasty belt.After you've discharged the tube, the HT lead can be disconnected and the component replaced.Discharge the tube again before replacing the HT lead.I have never liked doing this, it always makes me sweat. Which is ironic as just when I really don't want a belt, I make myself more conductive.If you're not really sure, don't do it. Try and work with your left hand in your pocket, keep it there.

author: mattbrockuk
author_rank: Contributor
timestamp: January 13, 2017, 12:31:40 pm
content: Makes me wonder if to strip it for bits and just obtain another one :-)I'm not sure if its worth the time looking at it... for what i paid for it £50 with 2x anayliser cards.. i may as well buy another one .. i think the anayliser cards are worth more than £50 each.

author: mattbrockuk
author_rank: Contributor
timestamp: January 13, 2017, 01:58:17 pm
content: Out of interest... if i did want to attempt this... can you actually get a replacement HT lead / transformer easily

author: CJay
author_rank: Super Contributor
timestamp: January 13, 2017, 02:06:41 pm
content: The HT lead is unlikely to be replaceable although some were. I have in the past spliced EHT leads on monochrome LOPTX, it works but you have to be careful and make sure to make a smooth solder joint or you get corona discharge.I'd be a lot more wary of doing that on a colour display as the EHT is roughly twice that of a monchrome.It's possible the CRT is just dirty around the anode cap, that can cause the sort of noises you're hearing, it's also possible it's the TX itself, if you feel happy to power it back on with the case removed then you may be able to see the discharge in a darkened room.As for replacing the LOPTX, it may be available but if you can obtain another 16500 for £50, it's not going to be worth it. Might be better to keep it for spares for a replacement one.If you were really adventurous, it may be possible to replace the monitor with an LCD ut again, cost/value is debatable

author: mattbrockuk
author_rank: Contributor
timestamp: January 13, 2017, 02:25:06 pm
content: Thanks guys, food for thought!I am hoping to obtain one of the 'scope cards for it, thats of more interest than the logic analyser - esp. with being able to drive it over the network too (thats the other option... disable the CRT and just use it as a network unit i guess) - although not as cool.

author: vealmike
author_rank: Regular Contributor
timestamp: January 13, 2017, 03:07:29 pm
content: As CJay has given you most of the info...Remove casing, connect to wall with a long mains lead. Turn power on at wall socket. Dim lights and observe corona / discharge. Probably HT lead.Remove power at wall, discharge tube. Remove HT lead. Suspend lead clear of circuitry and apply copious clear silicone sealant to break in insulation. Allow Silicone time to set. 2 applications may be needed. Reassemble. Repeat dark room test.This is not a difficult operation. But it is not one that you'd want to get wrong either.Do not electrocute yourself. Do not pass Go. Do not collect $200. Do not become conductive path from corona to ground. Do not blame me.

author: CJay
author_rank: Super Contributor
timestamp: January 13, 2017, 03:08:40 pm
content: Not as cool as you say, but, food for thought, you can often pick up broken clamshell portable DVD players, depending on the interface the 16500 uses for the monitor it may be possible to recycle the display into the analyser.It's also possible to buy laptop displays and an interface boarsd to convert them to VGA/RGB/Composite displays so all might not be lost if you are prepared to do a little hacking.

author: vealmike
author_rank: Regular Contributor
timestamp: January 13, 2017, 03:14:10 pm
content: 16500 had a touchscreen display, with just a FDD, a selector wheel, one(?) button and a power switch.It ran HP's own unix internally. God knows's what the interface to the display was. Probably CVBS, or RGB BS. But without the touchscreen the display was pretty useless.

author: CJay
author_rank: Super Contributor
timestamp: January 13, 2017, 03:16:03 pm
content: Missed a bit, if you do isolate the insulation breakdown to the lead, make sure to clean the lead to remove any surface dirt and carbonised residue or you'll just be making it more difficult to repair in a few weeks time.Same applies to the glass around the anode cap but don't clean off the black aquadag coating.ALso, try to obtain a neutral cure silicone where possible as the commonly available stuff is acid cure and can cause corrosion problems.I've never tried it but it might be possible to sheath the cable in silicone tubing, the extra flexible sort that's sold as 'silent' or quiet air hose by aquarium shops.Again, clean the cable first.It's not difficult to discharge the tube, two screwdrivers will do it, hold one firmly against the metalwork or black coating on the back of the tube, making sure the second is in good contact with the first, cross them and slide the second under the anode cap. Try not to jump as it will make a crack sound.Probably best to turn off the 16500 and unplug it first of course

author: CJay
author_rank: Super Contributor
timestamp: January 13, 2017, 03:26:45 pm
content: yeah, but the touchscreen was a matrix of infra red beams so I think it'll be built into the bezel rather than on the tube

author: stj
author_rank: Super Contributor
timestamp: January 13, 2017, 08:09:48 pm
content: put a frequency counter on the video sync pins of the monitor connector.some of the old HP stuff is VGA compatable.(31-32KHz horizontal, 50-60Hz vertical)

author: artag
author_rank: Super Contributor
timestamp: January 14, 2017, 06:07:58 pm
content: I've got a couple of these that you're welcome to for spares. I'm in bedfordshire, UK.

author: helius
author_rank: Super Contributor
timestamp: January 14, 2017, 07:01:51 pm
content: The 16500 display is not VGA; it is 576x368 at 25 kHz horizontal, 59.95 Hz vertical frequency.There was an external monitor interface option on the 16500B with a VGA-style connector, but a multisync monitor would usually be needed to use it. The 16500A had no external monitor option, as the interface card panel was taken up by the second floppy disk drive.

author: CJay
author_rank: Super Contributor
timestamp: January 15, 2017, 05:18:22 pm
content: Quote from: helius on January 14, 2017, 07:01:51 pmEGA?

author: stj
author_rank: Super Contributor
timestamp: January 15, 2017, 06:37:33 pm
content: convert it.http://www.sintron-hk.com/GBS-8220-arcade-game-RGB-CGA-TO-VGA-video-converter-P2699965.aspxyou even get a second output for the back of the case

author: helius
author_rank: Super Contributor
timestamp: January 15, 2017, 11:25:07 pm
content: Quote from: CJay on January 15, 2017, 05:18:22 pmIt has even less in common with EGA (approximately nothing).Quote from: stj on January 15, 2017, 06:37:33 pmThe specifications listed on that page do not indicate compatibility with 25 kHz, analog signals. Regardless, there isno possibility for external display outputon the 16500A without cutting holes in the bottom.

author: stj
author_rank: Super Contributor
timestamp: January 16, 2017, 12:28:16 am
content: the sintron pcb will convert 25KHz - it's what most customers use it for.we fit them in arcade machines to replace 25KHz crt monitors wih vga lcd panels.

author: CJay
author_rank: Super Contributor
timestamp: January 16, 2017, 09:57:07 am
content: Quote from: helius on January 15, 2017, 11:25:07 pmI had a vague recollection that the line frequency for EGA was in the 20KHz range, it can be ~21.5KHz in hi res mode so it's possible a monitor listing compatibility with EGA could be twiddled to synce, but you are correct, it's not an exact match and of course, video levels are TTL with intensity select too.

author: Gyro
author_rank: Super Contributor
timestamp: January 16, 2017, 10:14:52 am
content: All possible options but I suspect that if the OP does the 'look in the dark with the cover off' test (best with dark adapted eyes) followed by a decent cleanup then the CRT section with probably be just fine. It's not uncommon for dusty gear that has been left idle for a while, especially somewhere cold or humid.

author: mattbrockuk
author_rank: Contributor
timestamp: January 16, 2017, 01:41:35 pm
content: Hi guysThanks for the responses... i'm going to attempt it... pondering if its a good excuse to get a HV multimeter probe (CRT discharge)... or i guess i could just use two screwdrivers!Matt

author: vealmike
author_rank: Regular Contributor
timestamp: January 17, 2017, 08:26:45 am
content: There are two basic methods.1. Two screwdrivers.Screwdriver A is inserted in one of the GND screws fixing the front corner of the CRT to the case. Metal shaft of screwdriver B is held firmly against metal shaft of screwdriver A and checking A is still GNDed slid under the HT lead cap.Advantage: See method 2 disadvantage.Disadvantage: If the screwdrivers come apart, then you have one in each hand, one connected to GND, one to HT. The handles should insulate you, but if they don't, any belt goes straight across your chest, which means through the (quite vital yet easily disrupted by electric shocks) pumpy thing that's keeping you alive.2. Single Screwdriver & croc clip lead.Attach croc clip lead to GND point as above. Attach other end to screwdriver. Put left hand in pocket, using right hand, slide screwdriver under HT lead cap.Advantage: see method 1 disadvantage.Disadvantage: Flimsy croc lead could come off. Nowhere near as low an impedance path as method 1, meaning juice is more likely to flow through the electron herder hanging off the end of the screwdriver.I'm paranoid, I don't like doing this.

author: CJay
author_rank: Super Contributor
timestamp: January 17, 2017, 09:29:04 am
content: First time out discharging a CRT is scary, interesting thing to note though, a *lot* of monitors seem to self discharge and often there's little to no charge on the anode.That's not to say you don't have to be careful, you really do but once you've the knack of it, it's not at all difficult to do.Be careful when removing the cap, there's a couple of types, one's made of springy folded sheet metal, pushing down on the bump of the cap and squeezing to one side will release it, the other type is spring wire and they can be quite a bit more tricky to remove.Good luck.

author: Gyro
author_rank: Super Contributor
timestamp: January 17, 2017, 10:09:46 am
content: Absolutely thefirstthing to do islookthough - the darkened room with the cover off. You don't want to disturb anything until you have located the corona dicharge location - you might not need to even disturb the tube connector if it turns out that it's something like the EHT lead sitting too close to a bit of the chassis.Discharging the tube isn't nearly as scary as it sounds! Firstly it's a very small tube, when you compare it with an old 26" colour TV CRT, so it's capacitance is much smaller. Secondly it wouldn't be working at anything like the same EHT voltage... a few kV vs 26kV in a TV. In terms of energy being CV^2 you're in much lower territory. Just securely attach a thinish piece of hookup wire to the chassis, and the other end to the shaft of a screwdriver with a reasonable plastic handle, slide it under the cap until you can feel it touch metal, job done, and one handed. [Edit: Ideally you want a bit of impedance in the circuit anyway to limit the peak current through the joint between the connector and tube internal coating]. Most EHT caps are the two wing type, slide it sideways (relative to the wire) until one wing releases and then slide it the other. Put it back on the same way but applying downward pressure at the same time.Just to labour the point... Look and listen for the discharge first, it will save you loads of time and effort.

author: CJay
author_rank: Super Contributor
timestamp: January 17, 2017, 11:13:25 am
content: Quote from: Gyro on January 17, 2017, 10:09:46 amNo, sorry, that's just not true.A monochrome tube might have 'a few KV', most colour tubes will have 15-35KV (higher definition tubes tend to have higher voltages IIRC) and the size of the tube has little to do with the voltage.Totally agree on the dark room check though, definitely the first thing to check.I'd also be checking the board for bad solder joints, the holes for the LOPTX are often much larger than the pins and can be prone to dry joints

author: mattbrockuk
author_rank: Contributor
timestamp: January 17, 2017, 01:04:22 pm
content: Thanks again guys... hopefully will get round to doing this at weekend.Obviously the arcing isn't a great situation for it to be in... but I'm guessing its unlikely to catch on fire or go kaboom if i fire it up for a few seconds with the back off watching, just wondering if to do it in the kithcen whilst the wifes out or not... ;-)

author: Gyro
author_rank: Super Contributor
timestamp: January 17, 2017, 03:16:13 pm
content: Oops, didn't realize the HP16500 had a colour display, as you say then...Still, at worst the OP should expect a few muffled crackles from underneath the EHT connector skirt, nothing to get aprehensive about.

author: TomBombadil
author_rank: Newbie
timestamp: November 07, 2017, 08:30:50 am
content: Hello, are the spares mentioned still available?