On Sunday 08 February 2009 07:17:32 pm Ethan Dicks wrote: I'd think that probably any place that handles lead-acid batteries should be able to take them off your hands. I'll probably be doing something similar with the gels I end up with in the UPSs I have to poke through here. I'd also figure that any place doing a fair amount of business in car batteries shouldn't object to adding some gels to the pile. How much do those amount to in terms of bulk? I might be interested in taking a look if it's not too much. I'm pleasantly surprised on this list with fair regularity. :-) That having been the case with these scopes, I'm beginning to wonder, how easy is it to find one these days, and what might it take to get my hands on one? -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin

I am pretty sure I have a schematic for a 1-valve (other than the CRT) 'scope. Yes, there were soem semiconductor diodes in the PSU circuit, but no transistors or ICs (or other active components). It was published in one of the UK magazines back in the 1950s, and was intended for use in repairing valve TVs (where signal amplitudes were pretty hiyh). So there wa no Y amplifier, the input when to the Y plates. The vlave was, IIRC, a thyratron, used to make a simple timebase. -tony

On Mon, 9 Feb 2009, Roy J. Tellason wrote: Look for the model 230? On the 215 (15 MHz, dual trace) I could not get an adequate cat's-eye pattern for doing drive alignment (with an analog alignment diskette). Perhaps somebody with more skill and "tricks of the trade" might be able to, but the spec for alignment seems to be "20 MHz, dual trace"

On Mon, 9 Feb 2009, Roy J. Tellason wrote: not common, but there are some. I saw an MS-15 (single trace? 15MHz?) that is fairly cheap

Worse than that, as you mention in passing, in some designs the battery acts as a shunt regulator and stabilises the votlage on one of the main supply lines. A number of classic computers used a 4-cell NiCd pack as the supply _and regulator_ for the nominal 5V line. The Epson HX20 certainly does, I think the PX8 does too. There _may_ be a protection circuit to limit the voltage if the battery goes open-circuit, but it's best not to depend on this. This depends -- a lot -- on the HP calculator. The 'classic series' _without card readers *35, 45, 55, 70, 80) have a mains adapter which is a spearate 4.2V voltage-regualted supply to run the calculator and a 55mA constant-current supply to charge the NiCd pack, These machines work fine -- and safely -- on the adapter with no batterty fitted. The 65 and 67 (with card readers) run the card reader chip off the battery directly. With these, plugging the adapter in without a battery to clamp the voltage can daamge the card reader sense amplidier chip. This is more of a problem with the 65 -- IIRC the chip was redesigned for the 67 and is a lot more tolerant of overvoltage. The Woodstock (20 series) and Spice (30 seires) use a 2-cell NiCd pack and a simple charger. Tghe battery here acts as a smoothing and votlage limiting deviee./ Without it the calculator diesn't work. Worse than that, on -C (continuous memory) models, certainly Woodstocks, the voltage current) is still supplied to the RAM chip and is high enough to either damage the latter (STO/RCL/program storage doesn't work) or damage the ACT (processor chip) The Topcats (90 series) have a circuit in them to load the charger if the battery terminal voltage tries to exceed the Vss (logic supply) rail. This generally allows the machine to run from the charger with no battery installed, but the printer and card reader (97) won't work. Note that this cicuit will try to pull the battery voltage down to 0 if the power converter circuit fails (e.g. if the oscillator transistor goes open-circuit)m and gets hot and bothered doing so. One to watch for. Since this circuit is after the powr switch, I suspect the (very rare) 95C has the same problem with damage to the RAM chips if powered from the adapter with no battery fitted. I don't have a 95C, and when I borrowed one to invetigate I certain;y didn't try this!. -tony

I am pretty sure my Microwriter, an MW4 model, has a zener diode across the battery pack to protect the machine if the battery goes open. Incidnetally, one thing to watch for on this machine is that the power 'swtich (actually a pair of VMOS FETs in parallel) is in the -ve rail. There's a common positive to all the ICs and seaprate awitched and unswitched grounds. Alas my MW4 seems to have a ROM problem (in that some chords are misrecognised, it is not a switch/wirign/diode fault). If anyone has a klnown-good dump of the 2564 in an MW4, I'd be interested... -tony

[Lead Acid batteries] Yes. The HP110 and 110+ computers (aka 'Portable' and 'Portable Plus') use a 6V lead-acid battery. 3 2.5Ah Cyclon cells (the ones we've been discusssiong) fit perfectly, and in fact the 110+ service manual shows such a battery. But many machines shipped with a Panasonic 'block battery' -- a cuboidal 6V lead-acid thing.Nowadays it's easier to get the Cyclon cells. The HP9114 disk drive (both versions) also uses a 6V lead-acid battery inside a housing that includes the charger PCB. Again, most units seem to have come with a 'block battery' but 3 Cyclon cells fit the hosuing too. And IIRC the HP3421 Data Acquisition unit (an HPIL/HPIB digital multimeter/relay scanner/etc) uses a lead acid battery. I forget the exact type, I know I found a common Yuasa one would fit with minor mechancial changes. -tony