A dilemma: should I complain?

[tggzzz]

My newest fleabay toy has been delivered: a Tek THS720A scope. Isolated inputs, 2 channel, 100MHz 500MS/s, with an almost complete selection of accessories. It works nicely except that the NiCd battery is dead. Not really surprising given the age.

Condition was "used" without mentioning the battery. Price was very decent but not very low.

Replacement batteries (NiMH not NiCd) available for £34.

I have some old (i.e. unused expired) sub-c NiCds, and could probably disassemble the existing battery for its strange "collar" connector.

Options:

• do nothing, mains only operation. (Don't actually need the scope, let alone battery operation) - but that's par for the course here!
• buy near replacement
• hack my own
• complain to vendor

[Zenith]

It's hard to say because it isn't a thing I'd dream of buying - well not for more than a silly low price. If it's the listing I saw, it doesn't seem to be misleading, and you would expect them to point out if the battery was good. If it's not mentioned you can assume it isn't.

Is the NiMH pack an official replacement? I recall NiMH and NiCad have different charging requirements. £34 doesn't seem that bad for a battery pack that will work for years.

Since you have suitable NiCd cells on hand, I suggest taking that route.

[tggzzz]

It's hard to say because it isn't a thing I'd dream of buying - well not for more than a silly low price. If it's the listing I saw, it doesn't seem to be misleading, and you would expect them to point out if the battery was good. If it's not mentioned you can assume it isn't.

Is the NiMH pack an official replacement? I recall NiMH and NiCad have different charging requirements. £34 doesn't seem that bad for a battery pack that will work for years.

Since you have suitable NiCd cells on hand, I suggest taking that route.

Yes, yes, and probably

NiMH have lower charging currents and are less tolerant of trickle overcharging. I'm not sure whether the charger would or wouldn't adapt to NiMH, but the much earlier PUJT-based Tek1502 charger is a right royal bugger.

I have put that OCXO under the (frequency) microscope, but haven't written anything up yet. TLDR: they are bloody good, especially for the money

[MED6753]

Since the scope is meant for portable operation technically with dead batteries it isn't functional. But is it worth an outright complaint? That's debatable. I would at least mention to the seller that the batteries were dead and see if he offers up anything. If he responds negatively or gives no response then threaten him with a formal complaint.

[bd139]

It's old and quite frankly this was likely to be a problem so I would foot the £34 for a battery.

[tggzzz]

Both good points.

I'm concerned about the charging currents for a 2800mAh NiCd (original) vs a 4000mAh NiMH (fleabay) vs 1500mAh (my cells).

There is one NiCd for £72, but I'm not prepared to spend that.

I think I'll have to try to reverse engineer the charger, to see what it won't do to a battery.

[Zenith]

It's old and quite frankly this was likely to be a problem so I would foot the £34 for a battery.

That assumes that the £34 NiMH pack is a plug in replacement, which is why I asked whether it was an official spare. That sounds very cheap for a genuine Tek spare. If it is an official spare the charger might be part of the pack or there might be recommended modifications to be made to the scope. If it's just an NiMH pack with the same form factor as the original NiCd pack, it's asking for trouble to just bung it in.

I've come across a few things with NiCd pack options. Usually some previous owner has removed the damned thing. Once or twice I've had to deal with a festering pile of toxic waste that was once a NiCd pack.

Rechargeable battery packs are a declining asset from day one, so if you buy any rechargeable item; a power tool, a laptop, whatever, it's a reasonable bet that the rechargeable battery isn't much good. NiCd packs, long after the maker has dropped support for the item, are going to present particular problems.

[BU508A]

You could ask TERRA Operative from the TEA EEVBlog. He seems to be quite experienced with the THS 720 scopes.

[bd139]

It's old and quite frankly this was likely to be a problem so I would foot the £34 for a battery.

That assumes that the £34 NiMH pack is a plug in replacement, which is why I asked whether it was an official spare. That sounds very cheap for a genuine Tek spare. If it is an official spare the charger might be part of the pack or there might be recommended modifications to be made to the scope. If it's just an NiMH pack with the same form factor as the original NiCd pack, it's asking for trouble to just bung it in.

I've come across a few things with NiCd pack options. Usually some previous owner has removed the damned thing. Once or twice I've had to deal with a festering pile of toxic waste that was once a NiCd pack.

Rechargeable battery packs are a declining asset from day one, so if you buy any rechargeable item; a power tool, a laptop, whatever, it's a reasonable bet that the rechargeable battery isn't much good. NiCd packs, long after the maker has dropped support for the item, are going to present particular problems.

This is why I avoid things that use NiCd cells completely.

That HP 427A was a notable example where I had to build a complete battery eliminator!

[tggzzz]

This is why I avoid things that use NiCd cells completely.

That HP 427A was a notable example where I had to build a complete battery eliminator!

Your exercise for tomorrow is to try that with a Tek 1502; t'ain't easy. Easy ways are with another NiCd battery, or just ignore the PUJT PSU and replace the NiCd with a modern 240/12V brick PSU.

OTOH it is trivial with the Fluke 893A, and other Flukes with Nixie displays.

[bd139]

This is why I avoid things that use NiCd cells completely.

That HP 427A was a notable example where I had to build a complete battery eliminator!

Your exercise for tomorrow is to try that with a Tek 1502; t'ain't easy. Easy ways are with another NiCd battery, or just ignore the PUJT PSU and replace the NiCd with a modern 240/12V brick PSU.

OTOH it is trivial with the Fluke 893A, and other Flukes with Nixie displays.

Tek liked their horrible power supplies didn't they!

Nearly bought that 7000 crate the other day then looked and found out it was the SMPS variant which is shrouded in expensive mysteries most of the time. Will wait for a nice primitive linear one or a 454 I think.

[MED6753]

Tek liked their horrible power supplies didn't they!

Nearly bought that 7000 crate the other day then looked and found out it was the SMPS variant which is shrouded in expensive mysteries most of the time. Will wait for a nice primitive linear one or a 454 I think.

Nah, 99% of the time if the PSU is ticking it's a bloody tant.

[tggzzz]

This is why I avoid things that use NiCd cells completely.

That HP 427A was a notable example where I had to build a complete battery eliminator!

Your exercise for tomorrow is to try that with a Tek 1502; t'ain't easy. Easy ways are with another NiCd battery, or just ignore the PUJT PSU and replace the NiCd with a modern 240/12V brick PSU.

OTOH it is trivial with the Fluke 893A, and other Flukes with Nixie displays.

Tek liked their horrible power supplies didn't they!

Nearly bought that 7000 crate the other day then looked and found out it was the SMPS variant which is shrouded in expensive mysteries most of the time. Will wait for a nice primitive linear one or a 454 I think.

Disliked the 7000 crates when I was using them in the 70s. Always preferred the 465. Unfortunately >2 channels was often beneficial with random logic.

[tggzzz]

Decided not to complain; it would have been mean-spirited.

Decided not to attempt to use a NiMH replacement.

Decided to use some spare sub-C NiCd cells I have lying around waiting for Tek1502 to materialise. They are 2000mAh rather than the original 2800mAh, and slightly smaller.

First attempt to make my own battery pack worked, but was mechanically unpleasing.

Second attempt is fine; the only critical dimension is the diameter of the metal ring, since the corresponding contact in the case doesn't have much travel. There is latitude in the distance of the ring from the right hand end, since that end has the traditional spring contact. Job done.

Wonder what, if anything, I'll use the scope for. User manual mentions using the DVM to record mains line transients, or the scope to record missing mains cycles.

IMG_7816.JPG

[AVGresponding]

They're pretty useful for fault finding, especially in things like SMPS, because of the dual isolated inputs.

[tggzzz]

They're pretty useful for fault finding, especially in things like SMPS, because of the dual isolated inputs.

Exactly.

I have P6013 an P6015 and a couple of different HV diff probes. But no maths capability, so no power dissipation measurements.

I also hope such fault finding days are behind me

TEA indeed, but you know that