Elenco GF-8046 Function Generator - Page 1
Forum section: electronics / repair

author: Zapped
author_rank: Contributor
timestamp: June 11, 2017, 10:32:00 pm
content: I have an old Elenco GF-8046 Function Generator. The FG section works fine, no matter how long the device is turned on. The frequency counter section has a repeatable problem, where the frequency display goes blank after a minute or so. Once the display goes blank, it stays blank through a power cycle. Only after an extended power off period, does the display return, and then only for a few seconds until it blanks again.The frequency display (and counter?) itself is a snap-in module. It is a 5-digit LED display with no manufacturer listed, but has a P/N of G35APP0E. Also listed on the LED module is "Pwr: 5V 120 mA" and "Range: 0.200 Hz -> 9999.9 kHz. Since it has a frequency range specified, it sounds like it's also a counter? I measured voltages around the display unit. Schematic is attached. The display module has 5.0 V on the "Power from P62" input and 3.3 V on P64. These voltages are present whether the display is functioning or not. Likewise, U61, U63, U64, U65 all have 5.2V present on their Vin. U62 is delivering the proper plus and minus 5 V outputs. The TRIG.D LED LD63 works, and LD71 stays lit, even after the 7-segment display blanks out.This is a fairly common function generator. Before I go hunting further, I thought I'd ask here to see if anyone has already encountered this problem. I'm starting to suspect the LED display/counter module itself. Google searches for a suitable replacement for a "G35APP0E" module have not been fruitful. Any suggestions appreciated.

author: rdl
author_rank: Super Contributor
timestamp: June 12, 2017, 06:32:35 pm
content: You might look on ebay for a similar module. At one time those panel meter type counters with LED displays were fairly common. Intersil made basically a single chip solution specifically for this purpose and that could be what was used in this module.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 12, 2017, 06:44:31 pm
content: You should not have 3.3 V on P64, it is the output of the ALS00 and it should have TTL level, either 5V or 0V. Did you measure it with a multimeter?

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 07:45:54 pm
content: Quote from: PA0PBZ on June 12, 2017, 06:44:31 pmRMS value of a clock train input?

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 12, 2017, 08:14:58 pm
content: Quote from: Armadillo on June 12, 2017, 07:45:54 pmNot really RMS but some average between 5 and 0 volts yes.

author: Zapped
author_rank: Contributor
timestamp: June 12, 2017, 09:23:23 pm
content: Thanks for the suggestions. Just measured P64 with a scope. It's a TTL level signal, varying from +1.4 to +5.1 V. The signal itself is a square wave running at whatever frequency the generator is set to. The signal is present whether the display is working or not. Really starting to look like the problem is in the display module itself.Having trouble sourcing a replacement at Mouser or Digi-Key. Will try ebay. Is there a standard name for these "counter-plus-display-in-one" modules? May try cracking open the module itself to see if there is anything repairable in it.

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 10:55:32 pm
content: Your diagnosis is correct, I am afraid and yes this module is difficult to find even in my region.It would be interesting if you can still manipulate the LD70  to lights up?, otherwise its really confirmed pretty dead.Last resort would be to repair the module [if it can be accessed in]. If intermittent, it's still alive, won't you agree?Good luck with the repair.