Telequipment D34 oscilloscope

[llonen]

So one of my most detested repair scenarios, does anyone else dislike working on their own equipment. So I use this scope mostly for testing capacitors, relays and occasional testing of hot side switching PSU's and have had it for years it failed the other day which is an annoyance mostly since I like the scope's compactness and that it can be run from battery. Well the likely culprits included a leaking electrolytic and a bunch of really bad solder inc some split 100 nf caps see below although I have already started reworking the boards. It is now more or less functional besides the supply board putting out a lower voltage than expected. I am trying to source 6 tagged D cell rechargeable batteries for this, they all seem ridiculously over priced and I don't have a spot welder to attach my own tags

[redwire]

Re: Telequipment D34 oscilloscope

That's a nice piece of gear to have.
Almost all C and D cell NiMh rechageables are found to be one or two AA inside at around 2,500mAh or 5,000mAh. You can't get 10Ah at 9V easily... er I mean for a decent price.

[stj]

Re: Telequipment D34 oscilloscope

you could probably get several banks of AA into the same space including spring loaded holders.

what was the mAH on the originals anyway?

[llonen]

Re: Telequipment D34 oscilloscope

I managed to find several sets used in emergency lighting that I'm going to adapt. The originals were 4000 ma and based upon the 1800 ma draw from an external power supply I will get around 2 hours continuous usage from the new set when fully charged.

[stj]

Re: Telequipment D34 oscilloscope

well eneloop AA are 2400mAH so 12 of those in 2 packs of 6 will give you 4800mAH
ikea sells re-branded loops for about £5 for 4.

[llonen]

Re: Telequipment D34 oscilloscope

Would still leave me the problem of spot-welding tags to each cell, I would need the cells configured as pre-tagged which for some reason makes them very expensive. Maybe I should take this opportunity to construct one.

[stj]

Re: Telequipment D34 oscilloscope

no, AA's in those plastic holders with spring contacts - the holders will not add enough to the size to be a problem.
can you post a photo of the original pack so i can see the shape / cell orientation.

[llonen]

Re: Telequipment D34 oscilloscope

The setup inside the scope is quite tightly packed, the D cells are arranged in two packs of three stacked side by side being clamped in place with insulated metal brackets. With each pack occupying a tight spot on each side of the tube. Anyways I have an appropriate set on order now which leaves the question of a DC short spot welder which I have developed an interest in building.

[stj]

Re: Telequipment D34 oscilloscope

out of interest, what current does it pull from the pack?

[llonen]

Re: Telequipment D34 oscilloscope

I have not been able to measure that current draw from the pack yet due to the installed pack being non serviceable, when supplied via and bench supply in place of the battery pack the device draws about 1.8 amps.

[stj]

Re: Telequipment D34 oscilloscope

that's pretty high for a battery pack!

[llonen]

Re: Telequipment D34 oscilloscope

Well looking at the original installed packs they were rated at 4amp per D-cell the ones I am fitting turned out at 5amp's which in theory could give me anything approaching 3 hours use on battery.

[stj]

Re: Telequipment D34 oscilloscope

the capacity is not the same as the continuous permitted current though.
some cells are designed for long slow discharge while others are good for stuff like electric screwdrivers & such.

[llonen]

Re: Telequipment D34 oscilloscope

Looking at the data sheets for these batteries the discharge curves etc and assuming they are not some cheap copy, they are high temperature and suitable for a discharge rate of up-to 4amps. So should be more than suitable, I can always check charging and discharge characteristics before final installation.

[llonen]

Re: Telequipment D34 oscilloscope

Well it lives, packs have been installed and seem to be charging nicely, in operation as far as I can tell the discharge rate is around 1.4amps maybe a little less. This anomaly is to the way the packs are configured one bank of 5 cells at 6 volts and a single cell at 1.2 volts while this does not appear to be the case when referring back to the circuit with the battery pack shown as configured for one pack of 7.2 volts. I am not intending to investigate the discrepancy further.

[stj]

Re: Telequipment D34 oscilloscope

maybe it's used to create a negative bias for something - it's simpler than adding an invertor circuit.

[eccerr0r]

Re: Telequipment D34 oscilloscope

Yay for JINHAO P6100 scope probes!
(I have a pair shared between my scopes...)

[stj]

Re: Telequipment D34 oscilloscope

dont we all

i really should get some more so i can dedicate them and not worry about the trimmer caps.

[redwire]

Re: Telequipment D34 oscilloscope

I would make sure the charger is OK, schematic shows always on constant-current 340mA charging, no voltage limit.
Main power is a two-transistor DC-DC that is unregulated which seems unusual. No idea what the oddball cell is doing.

[llonen]

Re: Telequipment D34 oscilloscope

Yeah I measured around 200-300 ma charging current which is around that specified for the cells, I was concerned about the charging pcb since one of the failure modes encountered on this repair job was significant corrosion on the charging board and some corroded solder joints. This was likely related to the leaking electrolytic filter capacitor nearby. I had reworked most damage before getting around to take photos but if you look closely at the images you will see some of it.

I left the scope on charge over night to top off the new battery pack looking at bench meter I have 7.2 volts charging which seems reasonable. Due to the schematic showing always on its not my intention to leave the unit plugged in all the time.

Anyways I do like the JINHAO P6100 scope probes, they were obtained cheaply from Ebay, they seem to be of reasonable quality and hopefully not some knock off lol.