UNI-T UTG9005C function generator amplitude/voltage display dead

[monk]

Hello

I own a UNI-T UTG9005C function generator for some years and was quite satisfied with it. Unfortunately the amplitude/voltage display is dead now and I cannot find the problem. The last time I used the generator everything was ok.

Now the display is dead ... but not completely! The decimal points and the "V"/"mV" indicators lighten up, when I pressed the corresponding XXdB buttons. AND I noticed that ALL segments of both displays (frequency and voltage) lighten up for half a second or so, when I power on the generator. But the voltage display does it only one time. If I power down and immediately power up the generator, the voltage display stays dark (except the decimal points obviously). But if I wait for some minutes before powering on again, the voltage display does the test blink again.

I took the thing apart already and searched for the problem but all components are visually ok. Then I decided to swap out the chip that drives the voltage display but this also didn't help. I'm not very experienced in finding failures in electronics. I can identify a blown up capacitor and burnt resistors. I have a multimeter with capacity checker and a (very) old oscilloscope. (80's I guess) But I don't know how/where to start.

Please help me to identify the faulty part! (The generator itself works well. So I don't want to kill it completely)

Unfortunately I cannot take pictures right now, but I know that my generators pcb is exactly the same than in this thread:
https://www.eevblog.com/forum/testgear/uni-trend-utg9010c-10mhz-function-generator-with-her-clothes-removed-!-oh-dear/
(In fact UNI-T UTG9002C, UTG9005C, UTG9010C and UTG9025C all share the same board layout.)


The chip that drives the three seven segment displays of the voltage display is an intersil ICL7107CPLZ:
http://downloads.cdn.re-in.de/175000-199999/175374-da-01-en-IC_ICL_7107_CPLZ__DIL_40_ISL.pdf

And luckily I also found some pcb schematics for this device in a abandoned german board:
http://mschrod.de/SMF-Forum/index.php?action=dlattach;topic=49.0;attach=32

Thanks in advance for your suggestions! 
monk

[monk]

*bump* 

[Chris56000]

Hi!

I've purchased one and will post schematics as soon as I can draw them, but in the meantime:-

1) Check the +5V and -5V supplies to the 7107 chip on the front display PCB, pin 1 +ve and Pin 26 -ve;

2) You'll need to check the four ICs clustered round the AT89S52, 5U2 (74HC00), 5U3 (74HC00), 5U4 (74LS08), 5U5 (74HC4040) and 5U6 (74LS132), I recommend you obtain one of these:-

https://www.ebay.co.uk/itm/IC-Transistor-Tester-Detect-Meter-Maintenance-Digital-led-Tester-MOS-PNP-NPN/292443757028?hash=item44170199e4:g:8fIAAOSwT5tWMIfJ

Myself and several colleagues use these little testers and they will identify the "family" (LS, HC, HCT, etc) as well as the type, & they test linear and opto as well, but you'll need to remove each device for test!

3) Have a look at the three '9011 transistors in the top LH corner near the AT89S52 - these could be digit-select transistors!

Watch this space, schematics, test waveforms and other data to follow in due course when I get mine!

Chris Williams

PS!

It's now supplied in a white, dark blue and grey format front panel & case assembly with white knobbery, but sadly nobody thought of using s spellchecker when they made the revised front panel design! Also it's gone up £10 or so in the week or so since I ordered mine!

[monk]

Thanks for your help but unfortunately the whole thing died in a small cloud of smoke on friday.  Didn't want to waste even more time for investigations. So I decided to dump it and now its gone. Only came back to tell that. And now I see your posting. 
Thanks anyway! Perhaps this thread can help other unlucky owners in the future. 

[Chris56000]

Hi!!!!

I'vs still not received my unit yet but it'll  of go to waste as I'll draught the schematics and parts lists, etc.,  upload 'em to k04bb then then stick the Genny back on fleabay fterwards!

Thanks for letting us know!

Chris Williams

[Chris56000]

Hi!

Finally got round to trying out my Uni–T UTG9010C in a dark–grey case tonight and one of the output waveforms was badly distorted!

Only slight snag being, Uni–T have revised the pesky thing onto a tiny board a third of the size of the case made entirely of surface–mount components, so that's gone to the bottom of the "round to it!" pile until I can find the time to start scribbling it out!

The '7107 has gone, replaced by some sort of micro for the display driver and the thro' hole AT89S52 has also gone, replaced by another 44–pin QFP I can't read anything on, and there's minute silkscreen on the boards that'd take an electron–microscope to read!

Chris Williams

PS!

The Warranty Card (it was bought supposedly brand new!) said "Warranty Service Available In China Only!"