Help with Philips PM5139 synthesized function generator - Page 1
Forum section: electronics / beginners

author: pe1dnn
author_rank: Contributor
timestamp: March 02, 2023, 10:12:53 pm
content: In 2003 Ericsson closed a lot of its research centers including the one I worked. During clearing out the inventory I've got a Philips PM5139 synthesized function generator. last calibrated in 2001. It has been sporadically used by me since then, but last time I noticed the AC output cannot be adjusted anymore. After all these years I finally have a space to tinker with electronics again (I'm an electrical engineer bachelor but went to the dark side doing software...) and I want to repair the device. I do not have a service manual and I saw on this forum its hard to obtain. There are some sites claiming they have it but once downloaded it is the user manual and not the service manual.Below you find a lot of details, the Newbie guide instructed me to give as much detail as possible, so I tried my best to provide it.My question: Does anyone have an idea (e.g. is there a common fault that appears with the PM5139 or maybe its sister PM5138A). And does anybody have a clue how to get a service manual without running the risk of getting the user manual instead? Or any other idea how to proceed finding the fault?Details about the symptoms and what I tried so far.Symptoms.Startup shows no errors in self test. Frequency is adjustable, the different wave forms work including duty cycle. DC offset works. I can even still save settings which is amazing since after all this time the battery must be dead. Only on output I have a minimal signal and it does not change when I change the AC level, except when it switches range, i.e. when am at 1.99 Vpp and then reach 2.00 V then the display jumps to 2.0 V and I hear a click from the attenuator circuit and the output makes a step too. I think I get 2V pp then (can only check with a mutimeter though which shows RMS). But if I increase the amplitude setting it just stays the same. So only at the steps when the range switches the voltage changes.I checked the supply voltages, although I have no schematic I believe it is using +5V for the processor, +/- 10V and +/- 16V and the power rails look clean despite it still has the original Philips capacitors. Visual inspection of capacitors does not show any signs of leaking.Since I have output but the output is not changing at all when I change the AC setting (except at range switching) I think the problem is either the Amplitude circuit or whatever tells the Amplitude circuit what to do. I looked at the board and that part has 2 transistor packs (CA3183E and CA3127) but I also see A DAC312 which I think cannot be part of the Amplitude circuit but instead is maybe the DC offset part, which works. Without a schematic it is hard to tell.I found the service manual for the PM5193 which gave me a rough idea about the parts but the Amplitude circuit in that one is different using CMOS 4066 switches which my device does not have. I think the transistor packs are used instead so the PM5193 schematic is not usable for me.I also checked capacitors for shorts and a few transistors in circuit, not very accurate but at least no dead shorts. I did some measurements when the range switches because then the Amplitude circuit has to switch also but I did not see any change at the two transistor packs. Maybe I did it all wrong, testing blind without knowing if it is actual part of the Amplitude circuit at all. I also had to disconnect one board (I think it shapes the wave form, it has an Eprom with data for the sine wave) to get access and maybe the device does not like that. It did not produce errors; of course there will be no output signal but I was looking at the control voltages of the Amplitude circuit, at least that was the intention.The problem could also be the logic board, not telling the Amplitude board what to do. I think the Amplitude board has power but I'm not sure where to measure it exactly. The final Amplifier has +/- 16V but I do not suspect the Amplifier because then I would have seen at least a change when changing the AC setting.

author: pe1dnn
author_rank: Contributor
timestamp: March 03, 2023, 11:02:43 pm
content: More information on the PM5139 function generator with defective AC output voltage selection I try to repair.I now found out that the DAC312 is indeed part of the Amplitude module. A HCF4094 drives it and the output of it, which is the digital input to the DAC312 nicely counts up and down if I change the voltage. However the voltage on the output pins 18 and 19 of the DAC312 does not change at all. The DAC gets +10V and -10V supply and ground. I found an Analog Devices data sheet for it, it is a 12 bit D/A converter but they chose to ground the lowest significant 3 pins and therefore acts as a 9 bit D/A converter. The remaining input looks fine but the output does not.The DAC312 outputs a current and not a voltage but the resistance with an ohm meter is quite high, about 360k on the I+ output and 1M on the I- output. The voltage I measure is about 8.5V on both pins while I expected them to be different. The DAC312 is certainly suspect, but maybe it is not the DAC's fault.The DAC312 is connected to a mystery chip, I posted another question to the forum asking about that specific part.I included a picture of the Amplitude and Amplifier section here.Still puzzled why there is no service documentation anywhere for this device. Not even the cousins PM5138A and PM5136.

author: pe1dnn
author_rank: Contributor
timestamp: March 05, 2023, 05:33:53 pm
content: Just in case somebody else tries to fix a PM5139, the device is working properly again.In the previous response I identified DAC312 as being part of the amplitude control circuit. The mystery chip turns out to be an OQ0146, a custom Philips part. A chip with the same name is used in a PM3320 Oscilloscope for which service documentation can be found. Only snag is that the one in the Oscilloscope is a 20 pin SMD IC while the one in the OM5139 is a 18 Pin DIL package. On the 20 pin version pin 11 is skipped and pin 20 is also not mentioned in the schematic. When I used the same order on the 18 pin DIL then all pins from 12 to 19 are pin 11 to 18 on the DIL package. Measurements of the junctions that are supposed to be inside looked okay with this assumption. No definitive answers however.At least I got enough info to find out if something could be messing with the DAC312 output, and there was no reason for it to be wrong due to these components. I already checked the digital input of the DAC312, but the DAC312 also need 2 reference voltages. One reference is tied with a resistor to ground. The other one is supplied via a voltage divider. And there it hit me, this point has a smoothing electrolytic capacitor of 100ųF. This component decided to not be a capacitor anymore but change to a 2 Ohm resistor. Replacing it fixed the issue. And I'm very happy because this is just a static voltage so will not throw off the calibrationAttached the defective component and the replaired device.Notice is has a label "Radio WRN", this is not a radio station but the Radio group of Ericsson Labs Netherlands working on Wideband Radio Networks (UMTS) in 2002/2003.

author: Uppic
author_rank: Newbie
timestamp: April 30, 2025, 05:56:13 pm
content: Hello, do you have a copy of the PM5193 EPROM? Thank you very much.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 01, 2025, 10:15:13 am
content: the thread for the mysterious ic is :https://www.eevblog.com/forum/beginners/what-is-this-ic-367301/but as mentioned, there was the pinout count ??theses instruments casings : of Phillips where the same used by Fluke and Wayne Kerr, for say lcr's, maybe with some searchother similar models / brand(s) can or could be found ... but alas schematics where never found on many of them