Hafler DH330 FM Tuner Repair

After repair­ing the Nakamichi 610 FM Tuner / Preamp back in late 2023, I have been on the look­out for a FM tuner for the work­shop audio sys­tem. Since I already had the Hafler DH-110 Preamplifier, I set my sights on the DH-330 FM tuner which has the same styling as the 110 preamp.

After look­ing for sev­er­al years I final­ly came across an auc­tion list­ing for a “DH330 Stereo FM-AM Tuner — Not Tested Parts Or Repair audio unit”. I was the high bid­der at $36.00 with a rea­son­able ship­ping price. The unit looked to be in over­all great cos­met­ic con­di­tion, but had around 50% of the fre­quen­cy dis­play seg­ments not work­ing. I also noticed from the auc­tion pic­tures that the stereo indi­ca­tor was­n’t lit up with a strong sig­nal present. Even though the list­ing described this as an “FM-AM Tuner”, the DH-330 is a FM only tuner. Something eas­i­ly over­looked by the sell­er as many of the com­po­nent tuners of this era were AM-FM band devices.

After receiv­ing the unit I imme­di­ate­ly opened it up to check for a prop­er fuse and gave it a though visu­al inspec­tion espe­cial­ly look­ing for bulging or leak­ing capac­i­tors. Looking at the date code on many of the IC’s this unit was built in 1985, mak­ing it over 40 years old.

The dis­plays are a known issue on this mod­el and based on how many of the seg­ments were non-func­tion­al my guess is that this unit had seen many thou­sand hours of use.
The dis­play is a NSM-4005A man­u­fac­tured by National Semiconductor Optoelectronics divi­sion. The dis­play is an inte­grat­ed cir­cuit board fea­tur­ing a four dig­it red 0.5″ sev­en seg­ment LED dis­play with an onboard ser­i­al input dis­play dri­ver and a ter­mi­nal area with pads and thru-holes.

I did remove the red dis­play fil­ter and white light shield for the seg­ments from the board to see if it might be pos­si­ble to replace the indi­vid­ual seg­ment LED’s. That would be a No, as the micro­scop­ic LED dies are bond­ed to the cir­cuit traces along with micro­scop­ic wire from the dies to oth­er cir­cuit traces.

Unfortunately National Semiconductor quite sud­den­ly quit pro­duc­tion of opto­elec­tron­ic prod­ucts short­ly after mak­ing this mod­ule.
I did con­sid­er try­ing to design and build a replace­ment mod­ule for a brief instant, but the time, mon­ey, and effort made me quick­ly place that idea on the back burner.

I was able to pow­er up the unit an per­form a quick func­tion­al check and it worked very well with the excep­tion of the dis­play and the stereo sig­nal indi­ca­tor. Based on that I decid­ed it would be worth­while to replace the 40+ year old elec­trolyt­ic capac­i­tors that had seen many hours if not years of on-time.

I end­ed up replac­ing 26 elec­trolyt­ic capac­i­tors, but stayed away from sev­er­al capac­i­tors in the RF sec­tions of the board. Only pow­er sup­ply and audio path capac­i­tors were replaced and the oth­ers were checked for capac­i­ty and ESR most­ly in circuit.

High qual­i­ty low-ESR Nichicon capac­i­tors were used on the pow­er sup­ply PC27D board, along with addi­tion­al heatsink fins on IC101 LM317T the 12.2 volt reg­u­la­tor which oper­ates fair­ly hot. I also added a heatsink to the 20 pin DIP IC104 DS8906N PLL Synthesizer IC which was also very warm / hot. All volt­ages were spot-on and AC rip­ple was vir­tu­al­ly non-existent.

It was time now to fig­ure out what was going on with the stereo indi­ca­tor LED. I test­ed the LED out of cir­cuit and it worked per­fect­ly so was replaced. The stereo indi­ca­tor is con­trolled by IC202 a HA12016 MPX Decoder IC pin 9 lamp dri­ver.
After a bit of research, I found an inter­est­ing thread over at audiokarma.org. I end­ed up mark­ing the orig­i­nal loca­tion of P200 the PLL mul­ti­plex oscil­la­tor adjust­ment poten­tiome­ter. Then check­ing the sol­der con­nec­tions which were good and then clean­ing the poten­tiome­ter with DeoxIT D5 clean­er and then adjust­ing the pot back to it’s orig­i­nal loca­tion. The stereo indi­ca­tor was now work­ing properly.

Not leav­ing well enough alone I decid­ed dive a bit deep­er into the rab­bit hole and researched the spec­i­fi­ca­tion sheet for the HA12016 IC. There is a pro­ce­dure there for prop­er­ly adjust­ing the oscil­la­tor. It requires remov­ing the inputs from pins 2 and 12 which required lift­ing one leg of C220 and R206 then short­ed the anten­na input.
A fre­quen­cy counter was then attached to TP7 and P200 was adjust­ed for 76 kHz ± 50 Hz. The new poten­tiome­ter posi­tion was only around 3–4 degrees off of the orig­i­nal adjust­ment, but I felt bet­ter know­ing a bit more about how the cir­cuit operated.

While I was at it I also adjust­ed the detec­tor trans­former des­ig­nat­ed L200. This is a dual tun­ing core trans­former with an upper and low­er phys­i­cal adjust­ment. The eas­i­est adjust­ment to get to is the upper core, but that con­trols audio dis­tor­tion and gen­er­al­ly should be left alone unless you have the prop­er equip­ment and exper­tise, which I do not have either of.

By con­nect­ing a mul­ti­me­ter mea­sur­ing DC volts across TP1 and TP2 pic­tured above, and with the unit tuned on fre­quen­cy to a strong sta­tion the low­er core can be adjust­ed for close to a zero volt read­ing on the mul­ti­me­ter. Be sure only the bot­tom core is adjust­ed and use a prop­er non-metal­lic adjust­ment tool for this pro­ce­dure. There is a small hole in the cir­cuit board to allow access from the back side of the board if a mul­ti-core adjust­ment tool isn’t available.

After search­ing many weeks for the obso­lete dis­play, I acci­dent­ly came across an Ebay sell­er with some “Kalex Digital Clock Displays” with a part num­ber match­ing my fail­ing unit. I took a chance and placed an order, and now had to wait for it to arrive.

While wait­ing I did a lot of clean­ing of resid­ual flux from cir­cuit boards and also cleaned all of the IC pins and sock­ets using DeoxIT D5 con­tact clean­er. The vol­ume poten­tiome­ter and head­phone jack were also cleaned. Interestingly the rear RCA line out jacks feed through con­tacts on the head­phone jack when no plug is insert­ed and could be a source of noise if not cleaned.

The screws hold­ing the pow­er trans­former to the back pan­el were a bit loose allow­ing it to sit at an odd angle which was cor­rect­ed by gen­tly twist­ing the trans­former and tight­en­ing the screws snug­ly.
I do not know what to think about the 4.7 Megohm resis­tor tied to ground from one of the AC line ter­mi­nals of the AUX AC pow­er jack on the back pan­el. The pow­er cord is non-polar­ized so this resis­tor has a 50/50 chance of being con­nect­ed to line or neu­tral of the AC pow­er cord. This is how it was orig­i­nal­ly designed accord­ing to the schematiics.

The dis­play arrived and I replaced the orig­i­nal dis­crete wires with a pin head­er and then sol­dered the new dis­play to the pin head­er. Upon pow­er up the dis­play worked prop­er­ly just like a new unit.
I am very pleased with the new addi­tion for the work­shop audio sys­tem and it looks great paired with the DH-110 pre­amp.
Now I am on the search for a Hafler SE-150 CD player …