Tektronix TDS3BAT rebuild

[cunningfellow]

NiMh will die an early death if left constant trickle charging.  They should be turned off at delta-peak.

I will not be leaving this NiMh battery in the scope all the time.

[Dave Wise]

How is the TDS3BAT charger wired?  Is it a chip that can be jumpered to support NiMH?

[cunningfellow]

Personally have no idea.  I just did a battery swap and am happy to not have it on charge all the time.  I rarely need it as a portable so just leave it out.

I think from memory someone here has had a closer look at the battery and the protocol.

[Dave Wise]

That might have been me.  If by protocol you mean the comm between pack and scope, I once got knowledgeable enough on the TI BQ2050 gas gauge to decode it on my own scope, but it's beside the point, which is the charger.  In the TDS3BATB that's a MAX1737 (high power) and a BQ2057 (low power).  They could not have used that in the TDS3BAT because the BQ2057 is for Lithium only.

[cunningfellow]

Sorry, Just popped it open to take some photos for you.

Front of board has Battery Fuel Guage, Quad OpAmp, Linear Reg and a few FETs

BQ2014
LP324
LM2936
4435 (Q2 SO8)
50WQ04

Back of board has µC, comparators and a large FET

PIC16C54A
LM339
LM339
M50P03

I am going to guess the charging is done by the PIC and I think because it has a C rather than an F in its name it is write once isn't it.

Doesn't look like an easy mod to change the charging logic

[Dave Wise]

Thanks for the pictures!

We see that Tek OEMed the board from PowerStream Technology in 1998.
The 50WQ04 is a schottky power rectifier
The 4435's are FDS4435 30V 9A P-channel power mosfets
The M50P03 is a 50A N-channel power mosfet
The FZT789 is a PNP power BJT
No inductors so no switching power supply, I bet that the big mosfet
and/or the BJT are wired as linear pass elements with the PIC pulsing them
to limit power dissipation.
You are correct that the PIC16C54A in plastic package is OTP, so we aren't
going to be changing the program or even seeing it.

One thing that is still easy is to insert an ammeter and measure the
current at full charge.  It might be small enough that your cells
can tolerate it.